GL_NV_vertex_program2 |

- Name
- Name Strings
- Contact
- Notice
- IP Status
- Status
- Version
- Number
- Dependencies
- Overview
- Issues
- New Procedures and Functions
- New Tokens
- Additions to Chapter 2 of the OpenGL 1.3 Specification (OpenGL Operation)
- Additions to Chapter 3 of the OpenGL 1.3 Specification (Rasterization)
- Additions to Chapter 4 of the OpenGL 1.3 Specification (Per-Fragment Operations and the Frame Buffer)
- Additions to Chapter 5 of the OpenGL 1.3 Specification (Special Functions)
- Additions to Chapter 6 of the OpenGL 1.3 Specification (State and State Requests)
- Additions to Appendix A of the OpenGL 1.3 Specification (Invariance)
- Additions to the AGL/GLX/WGL Specifications
- GLX Protocol
- Errors
- New State
- Revision History

Name |

NV_vertex_program2

Name Strings |

GL_NV_vertex_program2

Contact |

Pat Brown, NVIDIA Corporation (pbrown 'at' nvidia.com) Mark Kilgard, NVIDIA Corporation (mjk 'at' nvidia.com)

Notice |

Copyright NVIDIA Corporation, 2000-2002.

IP Status |

NVIDIA Proprietary.

Status |

Implemented in CineFX (NV30) Emulation driver, August 2002. Shipping in Release 40 NVIDIA driver for CineFX hardware, January 2003.

Version |

Last Modified Date: 05/16/2004 NVIDIA Revision: 32

Number |

287

Dependencies |

Written based on the wording of the OpenGL 1.3 Specification and requires OpenGL 1.3. Written based on the wording of the NV_vertex_program extension specification, version 1.0. NV_vertex_program is required.

Overview |

This extension further enhances the concept of vertex programmability introduced by the NV_vertex_program extension, and extended by NV_vertex_program1_1. These extensions create a separate vertex program mode where the configurable vertex transformation operations in unextended OpenGL are replaced by a user-defined program. This extension introduces the VP2 execution environment, which extends the VP1 execution environment introduced in NV_vertex_program. The VP2 environment provides several language features not present in previous vertex programming execution environments: * Branch instructions allow a program to jump to another instruction specified in the program. * Branching support allows for up to four levels of subroutine calls/returns. * A four-component condition code register allows an application to compute a component-wise write mask at run time and apply that mask to register writes. * Conditional branches are supported, where the condition code register is used to determine if a branch should be taken. * Programmable user clipping is supported support (via the CLP0-CLP5 clip distance registers). Primitives are clipped to the area where the interpolated clip distances are greater than or equal to zero. * Instructions can perform a component-wise absolute value operation on any operand load. The VP2 execution environment provides a number of new instructions, and extends the semantics of several instructions already defined in NV_vertex_program. * ARR: Operates like ARL, except that float-to-int conversion is done by rounding. Equivalent results could be achieved (less efficiently) in NV_vertex program using an ADD/ARL sequence and a program parameter holding the value 0.5. * BRA, CAL, RET: Branch, subroutine call, and subroutine return instructions. * COS, SIN: Adds support for high-precision sine and cosine computations. * FLR, FRC: Adds support for computing the floor and fractional portion of floating-point vector components. Equivalent results could be achieved (less efficiently) in NV_vertex_program using the EXP instruction to compute the fractional portion of one component at a time. * EX2, LG2: Adds support for high-precision exponentiation and logarithm computations. * ARA: Adds pairs of components of an address register; useful for looping and other operations. * SEQ, SFL, SGT, SLE, SNE, STR: Add six new "set on" instructions, similar to the SLT and SGE instructions defined in NV_vertex_program. Equivalent results could be achieved (less efficiently) in NV_vertex_program with multiple SLT, SGE, and arithmetic instructions. * SSG: Adds a new "set sign" operation, which produces a vector holding negative one for negative components, zero for components with a value of zero, and positive one for positive components. Equivalent results could be achieved (less efficiently) in NV_vertex_program with multiple SLT, SGE, and arithmetic instructions. * The ARL instruction is extended to operate on four components instead of a single component. * All instructions that produce integer or floating-point result vectors have variants that update the condition code register based on the result vector. This extension also raises some of the resource limitations in the NV_vertex_program extension. * 256 program parameter registers (versus 96 in NV_vertex_program). * 16 temporary registers (versus 12 in NV_vertex_program). * Two four-component integer address registers (versus one single-component register in NV_vertex_program). * 256 total vertex program instructions (versus 128 in NV_vertex_program). * Including loops, programs can execute up to 64K instructions.

Issues |

This extension builds upon the NV_vertex_program extension. Should this specification contain selected edits to the NV_vertex_program specification or should the specs be unified? RESOLVED: Since NV_vertex_program and NV_vertex_program2 programs share many features, the main section of this specification is unified and describes both types of programs. Other sections containing NV_vertex_program features that are unchanged by this extension will not be edited. How can a program use condition codes to avoid extra computations? Consider the example of evaluating the OpenGL lighting model for a given light. If the diffuse dot product is negative (roughly 1/2 the time for random geometry), the only contribution to the light is ambient. In this case, condition codes and branching can skip over a number of unneeded instructions. # R0 holds accumulated light color # R2 holds normal # R3 holds computed light vector # R4 holds computed half vector # c[0] holds ambient light/material product # c[1] holds diffuse light/material product # c[2].xyz holds specular light/material product # c[2].w holds specular exponent DP3C R1.x, R2, R3; # diffuse dot product ADD R0, R0, c[0]; # accumulate ambient BRA pointsAway (LT.x) # skip rest if diffuse dot < 0 MOV R1.w, c[2].w; DP3 R1.y, R2, R4; # specular dot product LIT R1, R1; # compute expontiated specular MAD R4, c[1], R0.y; # accumulate diffuse MAD R4, c[2], R0.z; # accumulate specular pointsAway: ... # continue execution How can a program use subroutines? With subroutines, a program can encapsulate a small piece of functionality into a subroutine and call it multiple times, as in CPU code. Applications will need to identify the registers used to pass data to and from the subroutine. Subroutines could be used for applications like evaluating lighting equations for a single light. With conditional branching and subroutines, a variable number of lights (which could even vary per-vertex) can be easily supported. accumulate: # R0 holds the accumulated result # R1 holds the value to add ADD R0, R1; RET; # Compute floor(A)*B by repeated addition using a subroutine. Yes, # this is a stupid example. # # c[0] holds (A,B,0,1). # R0 holds the accumulated result # R1 holds B, the value to accumulate. # R2 holds the number of iterations remaining. MOV R0, c[0].z; # start with zero MOV R1, c[0].y; FLRC R2.x, c[0].x; BRA done (LE.x); top: CAL accumulate; ADDC R2.x, R2.x, -c[0].w; # decrement count BRA top (GT.x); done: ... How can conventional OpenGL clip planes be supported in vertex programs? The clip distance in the OpenGL specification can be evaluated with a simple DP4 instruction that writes to one of the six clip distance registers. Primitives will automatically be clipped to the half-space where o[CLPx] >= 0, which matches the definition in the spec. # R0 holds eye coordinates # c[0] holds eye-space clip plane coefficients DP4 o[CLP0].x, R0, c[0]; Note that the clip plane or clip distance volume corresponding to the o[CLPn] register used must be enabled, or no clipping will be performed. The clip distance registers allow for clip distance volumes to be computed more-or-less arbitrarily. To approximate clipping to a sphere of radius <n>, the following code can be used. # R0 holds eye coordinates # c[0].xyz holds sphere center # c[0].w holds the square of the sphere radius SUB R1.xyz, R0, c[0]; # distance vector DP3 R1.w, R1, R1; # compute distance squared SUB o[CLP0].x, c[0].w, R1.w; # compute r^2 - d^2 Since the clip distance is interpolated linearly over a primitive, the clip distance evaluated at a point will represent a piecewise-linear approximation of the true distance. The approximation will become increasingly more accurate as the primitive is tesselated more finely. How can looping be achieved in vertex programs? Simple loops can be achieved using a general purpose floating-point register component as a counter. The following code calls a function named "function" <n> times, where <n> is specified in a program parameter register component. # c[0].x holds the number of iterations to execute. # c[1].x holds the constant 1.0. MOVC R15.x, c[0].x; startLoop: CAL function (GT.x); # if (counter > 0) function(); SUBC R15.x, R15.x, c[1].x; # counter = counter - 1; BRA startLoop (GT.x); # if (counter > 0) goto start; endLoop: ... More complex loops (where a separate index may be needed for indexed addressing into the program parameter array) can be achieved using the ARA instruction, which will add the x/z and y/w components of an address register. # c[0].x holds the number of iterations to execute # c[0].y holds the initial index value # c[0].z holds the constant -1.0 (used for the iteration count) # c[0].w holds the index step value ARLC A1, c[0]; startLoop: CAL function (GT.x); # if (counter > 0) function(); # Note: A1.y can be used for # indexing in function(). ARAC A1.xy, A1; # counter = counter - 1; # index += loopStep; BRA startLoop (GT.x); # if (counter > 0) goto start; endLoop: ... Should this specification add support for vertex state programs beyond the VP1 execution environment? No. Vertex state programs are a little-used feature of NV_vertex_program and don't perform particularly well. They are still supported for compatibility with the original NV_vertex_program spec, but they will not be extended to support new features. How are NaN's be handled in the "set on" instructions (SEQ, SGE, SGT, SLE, SLT, SNE)? What about MIN, MAX? SSG? When doing condition code tests? Any of these instructions involving a NaN operand will produce a NaN result. This behavior differs from the NV_fragment_program extension. There, SEQ, SGE, SGT, SLE, and SLT will produce 0.0 if either operand is a NaN, and SNE will produce 1.0 if either operand is a NaN. For condition code updates, NaN values will result in "UN" condition codes. All conditionals using a "UN" condition code, except "TR" and "NE" will evaluate to false. This behavior is identical to the functionality in NV_fragment_program. How can the various features of this extension be used to provide skinning functionality similar to that in ARB_vertex_blend and ARB_matrix_palette? And how can that functionality be extended? Assume an implementation that allows application of up to 8 matrices at once. Further assume that v[12].xyzw and v[13].xyzw hold the set of 8 weights, and v[14].xyzw and v[15].xyzw hold the set of 8 matrix indices. Furthermore, assume that the palette of matrices are stored/tracked at c[0], c[4], c[8], and so on. As an additional optimization, an application can specify that fewer than 8 matrices should be applied by storing a negative palette index immediately after the last index is applied. Skinning support in this example can be provided by the following code: ARLC A0, v[14]; # load 4 palette indices at once DP4 R1.x, c[A0.x+0], v[0]; # 1st matrix transform DP4 R1.y, c[A0.x+1], v[0]; DP4 R1.z, c[A0.x+2], v[0]; DP4 R1.w, c[A0.x+3], v[0]; MUL R0, R1, v[12].x; # accumulate weighted sum in R0 BRA end (LT.y); # stop on a negative matrix index DP4 R1.x, c[A0.y+0], v[0]; # 2nd matrix transform DP4 R1.y, c[A0.y+1], v[0]; DP4 R1.z, c[A0.y+2], v[0]; DP4 R1.w, c[A0.y+3], v[0]; MAD R0, R1, v[12].y, R0; # accumulate weighted sum in R0 BRA end (LT.z); # stop on a negative matrix index ... # 3rd and 4th matrix transform ARLC A0, v[15]; # load next four palette indices BRA end (LT.x); DP4 R1.x, c[A0.x+0], v[0]; # 5th matrix transform DP4 R1.y, c[A0.x+1], v[0]; DP4 R1.z, c[A0.x+2], v[0]; DP4 R1.w, c[A0.x+3], v[0]; MAD R0, R1, v[13].x, R0; # accumulate weighted sum in R0 BRA end (LT.y); # stop on a negative matrix index ... # 6th, 7th, and 8th matrix transform end: ... # any additional instructions The amount of code used by this example could further be reduced using a subroutine performing four transformations at a time: ARLC A0, v[14]; # load first four indices CAL skin4; # do first four transformations BRA end (LT); # end if any of the first 4 indices was < 0 ARLC A0, v[15]; # load second four indices CAL skin4; # do second four transformations end: ... # any additional instructions Why does the RCC instruction exist? RESOLVED: To perform numeric operations that will avoid overflow and underflow issues. Should the specification provide more examples? RESOLVED: It would be nice.

New Procedures and Functions |

None.

New Tokens |

None.

Additions to Chapter 2 of the OpenGL 1.3 Specification (OpenGL Operation) |

Modify Section 2.11, Clipping (p. 39) (modify last paragraph, p. 39) When the GL is not in vertex program mode (section 2.14), this view volume may be further restricted by as many as n client-defined clip planes to generate the clip volume. ... (add before next-to-last paragraph, p. 40) When the GL is in vertex program mode, the view volume may be restricted to the individual clip distance volumes derived from the per-vertex clip distances (o[CLP0] - o[CLP5]). Clip distance volumes are applied if and only if per-vertex clip distances are not supported in the vertex program execution environment. A point P belonging to the primitive under consideration is in the clip distance volume numbered n if and only if c_n(P) >= 0, where c_n(P) is the interpolated value of the clip distance CLPn at the point P. For point primitives, c_n(P) is simply the clip distance for the vertex in question. For line and triangle primitives, per-vertex clip distances are interpolated using a weighted mean, with weights derived according to the algorithms described in sections 3.4 and 3.5. (modify next-to-last paragraph, p.40) Client-defined clip planes or clip distance volumes are enabled with the generic Enable command and disabled with the Disable command. The value of the argument to either command is CLIP PLANEi where i is an integer between 0 and n; specifying a value of i enables or disables the plane equation with index i. The constants obey CLIP PLANEi = CLIP PLANE0 + i. Add Section 2.14, Vertex Programs (p. 57). This section supersedes the similar section added in the NV_vertex_program extension and extended in the NV_vertex_program1_1 extension. The conventional GL vertex transformation model described in sections 2.10 through 2.13 is a configurable, but essentially hard-wired, sequence of per-vertex computations based on a canonical set of per-vertex parameters and vertex transformation related state such as transformation matrices, lighting parameters, and texture coordinate generation parameters. The general success and utility of the conventional GL vertex transformation model reflects its basic correspondence to the typical vertex transformation requirements of 3D applications. However when the conventional GL vertex transformation model is not sufficient, the vertex program mode provides a substantially more flexible model for vertex transformation. The vertex program mode permits applications to define their own vertex programs. Section 2.14.1, Vertex Program Execution Environment The vertex program execution environment is an operational model that defines how a program is executed. The execution environment includes a set of instructions, a set of registers, and semantic rules defining how operations are performed. There are three vertex program execution environments, VP1, VP1.1, and VP2. The environment names are taken from the mandatory program prefix strings found at the beginning of all vertex programs. The VP1.1 execution environment is a minor addition to the VP1 execution environment, so references to the VP1 execution environment below apply to both VP1 and VP1.1 execution environments except where otherwise noted. The vertex program instruction set consists primarily of floating-point 4-component vector operations operating on per-vertex attributes and program parameters. Vertex programs execute on a per-vertex basis and operate on each vertex completely independently from the processing of other vertices. Vertex programs execute without data hazards so results computed in one operation can be used immediately afterwards. Vertex programs produce a set of vertex result vectors that becomes the set of transformed vertex parameters used by primitive assembly. In the VP1 environment, vertex programs execute a finite fixed sequence of instructions with no branching or looping. In the VP2 environment, vertex programs support conditional and unconditional branches and four levels of subroutine calls. The vertex program register set consists of six types of registers described in the following sections. Section 2.14.1.1, Vertex Attribute Registers The Vertex Attribute Registers are sixteen 4-component vector floating-point registers containing the current vertex's per-vertex attributes. These registers are numbered 0 through 15. These registers are private to each vertex program invocation and are initialized at each vertex program invocation by the current vertex attribute state specified with VertexAttribNV commands. These registers are read-only during vertex program execution. The VertexAttribNV commands used to update the vertex attribute registers can be issued both outside and inside of Begin/End pairs. Vertex program execution is provoked by updating vertex attribute zero. Updating vertex attribute zero outside of a Begin/End pair is ignored without generating any error (identical to the Vertex command operation). The commands void VertexAttrib{1234}{sfd}NV(uint index, T coords); void VertexAttrib{1234}{sfd}vNV(uint index, T coords); void VertexAttrib4ubNV(uint index, T coords); void VertexAttrib4ubvNV(uint index, T coords); specify the particular current vertex attribute indicated by index. The coordinates for each vertex attribute are named x, y, z, and w. The VertexAttrib1NV family of commands sets the x coordinate to the provided single argument while setting y and z to 0 and w to 1. Similarly, VertexAttrib2NV sets x and y to the specified values, z to 0 and w to 1; VertexAttrib3NV sets x, y, and z, with w set to 1, and VertexAttrib4NV sets all four coordinates. The error INVALID_VALUE is generated if index is greater than 15. No conversions are applied to the vertex attributes specified as type short, float, or double. However, vertex attributes specified as type ubyte are converted as described by Table 2.6. The commands void VertexAttribs{1234}{sfd}vNV(uint index, sizei n, T coords[]); void VertexAttribs4ubvNV(uint index, sizei n, GLubyte coords[]); specify a contiguous set of n vertex attributes. The effect of VertexAttribs{1234}{sfd}vNV(index, n, coords) is the same (assuming no errors) as the command sequence #define NUM k /* where k is 1, 2, 3, or 4 components */ int i; for (i=n-1; i>=0; i--) { VertexAttrib{NUM}{sfd}vNV(i+index, &coords[i*NUM]); } VertexAttribs4ubvNV behaves similarly. The VertexAttribNV calls equivalent to VertexAttribsNV are issued in reverse order so that vertex program execution is provoked when index is zero only after all the other vertex attributes have first been specified. The set and operation of vertex attribute registers are identical for both VP1 and VP2 execution environment. Section 2.14.1.2, Program Parameter Registers The Program Parameter Registers are a set of 4-component floating-point vector registers containing the vertex program parameters. In the VP1 execution environment, there are 96 registers, numbered 0 through 95. In the VP2 execution environment, there are 256 registers, numbered 0 through 255. This relatively large set of registers is intended to hold parameters such as matrices, lighting parameters, and constants required by vertex programs. Vertex program parameter registers can be updated in one of two ways: by the ProgramParameterNV commands outside of a Begin/End pair or by a vertex state program executed outside of a Begin/End pair (vertex state programs are discussed in section 2.14.3). The commands void ProgramParameter4fNV(enum target, uint index, float x, float y, float z, float w) void ProgramParameter4dNV(enum target, uint index, double x, double y, double z, double w) specify the particular program parameter indicated by index. The coordinates values x, y, z, and w are assigned to the respective components of the particular program parameter. target must be VERTEX_PROGRAM_NV. The commands void ProgramParameter4dvNV(enum target, uint index, double *params); void ProgramParameter4fvNV(enum target, uint index, float *params); operate identically to ProgramParameter4fNV and ProgramParameter4dNV respectively except that the program parameters are passed as an array of four components. The error INVALID_VALUE is generated if the specified index is greater than or equal to the number of program parameters in the execution environment (96 for VP1, 256 for VP2). The commands void ProgramParameters4dvNV(enum target, uint index, uint num, double *params); void ProgramParameters4fvNV(enum target, uint index, uint num, float *params); specify a contiguous set of num program parameters. The effect is the same (assuming no errors) as for (i=index; i<index+num; i++) { ProgramParameter4{fd}vNV(target, i, ¶ms[i*4]); } The error INVALID_VALUE is generated if sum of <index> and <num> is greater than the number of program parameters in the execution environment (96 for VP1, 256 for VP2). The program parameter registers are shared to all vertex program invocations within a rendering context. ProgramParameterNV command updates and vertex state program executions are serialized with respect to vertex program invocations and other vertex state program executions. Writes to the program parameter registers during vertex state program execution can be maskable on a per-component basis. The initial value of all 96 (VP1) or 256 (VP2) program parameter registers is (0,0,0,0). Section 2.14.1.3, Address Registers The Address Registers are 4-component vector registers with signed 10-bit integer components. In the VP1 execution environment, there is only a single address register (A0) and only the x component of the register is accessible. In the VP2 execution environment, there are two address registers (A0 and A1), of which all four components are accessible. The address registers are private to each vertex program invocation and are initialized to (0,0,0,0) at every vertex program invocation. These registers can be written during vertex program execution (but not read) and their values can be used for as a relative offset for reading vertex program parameter registers. Only the vertex program parameter registers can be read using relative addressing (writes using relative addressing are not supported). See the discussion of relative addressing of program parameters in section 2.14.2.1 and the discussion of the ARL instruction in section 2.14.3.4. Section 2.14.1.4, Temporary Registers The Temporary Registers are 4-component floating-point vector registers used to hold temporary results during vertex program execution. In the VP1 execution environment, there are 12 temporary registers, numbered 0 through 11. In the VP2 execution environment, there are 16 temporary registers, numbered 0 through 15. These registers are private to each vertex program invocation and initialized to (0,0,0,0) at every vertex program invocation. These registers can be read and written during vertex program execution. Writes to these registers can be maskable on a per-component basis. In the VP2 execution environment, there is one additional temporary pseudo-register, "CC". CC is treated as unnumbered, write-only temporary register, whose sole purpose is to allow instructions to modify the condition code register (section 2.14.1.6) without overwriting the contents of any temporary register. Section 2.14.1.5, Vertex Result Registers The Vertex Result Registers are 4-component floating-point vector registers used to write the results of a vertex program. There are 15 result registers in the VP1 execution environment, and 21 in the VP2 execution environment. Each register value is initialized to (0,0,0,1) at the invocation of each vertex program. Writes to the vertex result registers can be maskable on a per-component basis. These registers are named in Table X.1 and further discussed below. Vertex Result Component Register Name Description Interpretation -------------- --------------------------------- -------------- HPOS Homogeneous clip space position (x,y,z,w) COL0 Primary color (front-facing) (r,g,b,a) COL1 Secondary color (front-facing) (r,g,b,a) BFC0 Back-facing primary color (r,g,b,a) BFC1 Back-facing secondary color (r,g,b,a) FOGC Fog coordinate (f,*,*,*) PSIZ Point size (p,*,*,*) TEX0 Texture coordinate set 0 (s,t,r,q) TEX1 Texture coordinate set 1 (s,t,r,q) TEX2 Texture coordinate set 2 (s,t,r,q) TEX3 Texture coordinate set 3 (s,t,r,q) TEX4 Texture coordinate set 4 (s,t,r,q) TEX5 Texture coordinate set 5 (s,t,r,q) TEX6 Texture coordinate set 6 (s,t,r,q) TEX7 Texture coordinate set 7 (s,t,r,q) CLP0(*) Clip distance 0 (d,*,*,*) CLP1(*) Clip distance 1 (d,*,*,*) CLP2(*) Clip distance 2 (d,*,*,*) CLP3(*) Clip distance 3 (d,*,*,*) CLP4(*) Clip distance 4 (d,*,*,*) CLP5(*) Clip distance 5 (d,*,*,*) Table X.1: Vertex Result Registers. (*) Registers CLP0 through CLP5, are available only in the VP2 execution environment. HPOS is the transformed vertex's homogeneous clip space position. The vertex's homogeneous clip space position is converted to normalized device coordinates and transformed to window coordinates as described at the end of section 2.10 and in section 2.11. Further processing (subsequent to vertex program termination) is responsible for clipping primitives assembled from vertex program-generated vertices as described in section 2.10 but all client-defined clip planes are treated as if they are disabled when vertex program mode is enabled. Four distinct color results can be generated for each vertex. COL0 is the transformed vertex's front-facing primary color. COL1 is the transformed vertex's front-facing secondary color. BFC0 is the transformed vertex's back-facing primary color. BFC1 is the transformed vertex's back-facing secondary color. Primitive coloring may operate in two-sided color mode. This behavior is enabled and disabled by calling Enable or Disable with the symbolic value VERTEX_PROGRAM_TWO_SIDE_NV. The selection between the back-facing colors and the front-facing colors depends on the primitive of which the vertex is a part. If the primitive is a point or a line segment, the front-facing colors are always selected. If the primitive is a polygon and two-sided color mode is disabled, the front-facing colors are selected. If it is a polygon and two-sided color mode is enabled, then the selection is based on the sign of the (clipped or unclipped) polygon's signed area computed in window coordinates. This facingness determination is identical to the two-sided lighting facingness determination described in section 2.13.1. The selected primary and secondary colors for each primitive are clamped to the range [0,1] and then interpolated across the assembled primitive during rasterization with at least 8-bit accuracy for each color component. FOGC is the transformed vertex's fog coordinate. The register's first floating-point component is interpolated across the assembled primitive during rasterization and used as the fog distance to compute per-fragment the fog factor when fog is enabled. However, if both fog and vertex program mode are enabled, but the FOGC vertex result register is not written, the fog factor is overridden to 1.0. The register's other three components are ignored. Point size determination may operate in program-specified point size mode. This behavior is enabled and disabled by calling Enable or Disable with the symbolic value VERTEX_PROGRAM_POINT_SIZE_NV. If the vertex is for a point primitive and the mode is enabled and the PSIZ vertex result is written, the point primitive's size is determined by the clamped x component of the PSIZ register. Otherwise (because vertex program mode is disabled, program-specified point size mode is disabled, or because the vertex program did not write PSIZ), the point primitive's size is determined by the point size state (the state specified using the PointSize command). The PSIZ register's x component is clamped to the range zero through either the hi value of ALIASED_POINT_SIZE_RANGE if point smoothing is disabled or the hi value of the SMOOTH_POINT_SIZE_RANGE if point smoothing is enabled. The register's other three components are ignored. If the vertex is not for a point primitive, the value of the PSIZ vertex result register is ignored. TEX0 through TEX7 are the transformed vertex's texture coordinate sets for texture units 0 through 7. These floating-point coordinates are interpolated across the assembled primitive during rasterization and used for accessing textures. If the number of texture units supported is less than eight, the values of vertex result registers that do not correspond to existent texture units are ignored. CLP0 through CLP5, available only in the VP2 execution environment, are the transformed vertex's clip distances. These floating-point coordinates are used by post-vertex program clipping process (see section 2.11). Section 2.14.1.6, The Condition Code Register The VP2 execution environment provides a single four-component vector called the condition code register. Each component of this register is one of four enumerated values: GT (greater than), EQ (equal), LT (less than), or UN (unordered). The condition code register can be used to mask writes to registers and to evaluate conditional branches. Most vertex program instructions can optionally update the condition code register. When a vertex program instruction updates the condition code register, a condition code component is set to LT if the corresponding component of the result is less than zero, EQ if it is equal to zero, GT if it is greater than zero, and UN if it is NaN (not a number). The condition code register is initialized to a vector of EQ values each time a vertex program executes. There is no condition code register available in the VP1 execution environment. Section 2.14.1.7, Semantic Meaning for Vertex Attributes and Program Parameters One important distinction between the conventional GL vertex transformation mode and the vertex program mode is that per-vertex parameters and other state parameters in vertex program mode do not have dedicated semantic interpretations the way that they do with the conventional GL vertex transformation mode. For example, in the conventional GL vertex transformation mode, the Normal command specifies a per-vertex normal. The semantic that the Normal command supplies a normal for lighting is established because that is how the per-vertex attribute supplied by the Normal command is used by the conventional GL vertex transformation mode. Similarly, other state parameters such as a light source position have semantic interpretations based on how the conventional GL vertex transformation model uses each particular parameter. In contrast, vertex attributes and program parameters for vertex programs have no pre-defined semantic meanings. The meaning of a vertex attribute or program parameter in vertex program mode is defined by how the vertex attribute or program parameter is used by the current vertex program to compute and write values to the Vertex Result Registers. This is the reason that per-vertex attributes and program parameters for vertex programs are numbered instead of named. For convenience however, the existing per-vertex parameters for the conventional GL vertex transformation mode (vertices, normals, colors, fog coordinates, vertex weights, and texture coordinates) are aliased to numbered vertex attributes. This aliasing is specified in Table X.2. The table includes how the various conventional components map to the 4-component vertex attribute components. Vertex Attribute Conventional Conventional Register Per-vertex Conventional Component Number Parameter Per-vertex Parameter Command Mapping --------- --------------- ----------------------------------- ------------ 0 vertex position Vertex x,y,z,w 1 vertex weights VertexWeightEXT w,0,0,1 2 normal Normal x,y,z,1 3 primary color Color r,g,b,a 4 secondary color SecondaryColorEXT r,g,b,1 5 fog coordinate FogCoordEXT fc,0,0,1 6 - - - 7 - - - 8 texture coord 0 MultiTexCoord(GL_TEXTURE0_ARB, ...) s,t,r,q 9 texture coord 1 MultiTexCoord(GL_TEXTURE1_ARB, ...) s,t,r,q 10 texture coord 2 MultiTexCoord(GL_TEXTURE2_ARB, ...) s,t,r,q 11 texture coord 3 MultiTexCoord(GL_TEXTURE3_ARB, ...) s,t,r,q 12 texture coord 4 MultiTexCoord(GL_TEXTURE4_ARB, ...) s,t,r,q 13 texture coord 5 MultiTexCoord(GL_TEXTURE5_ARB, ...) s,t,r,q 14 texture coord 6 MultiTexCoord(GL_TEXTURE6_ARB, ...) s,t,r,q 15 texture coord 7 MultiTexCoord(GL_TEXTURE7_ARB, ...) s,t,r,q Table X.2: Aliasing of vertex attributes with conventional per-vertex parameters. Only vertex attribute zero is treated specially because it is the attribute that provokes the execution of the vertex program; this is the attribute that aliases to the Vertex command's vertex coordinates. The result of a vertex program is the set of post-transformation vertex parameters written to the Vertex Result Registers. All vertex programs must write a homogeneous clip space position, but the other Vertex Result Registers can be optionally written. Clipping and culling are not the responsibility of vertex programs because these operations assume the assembly of multiple vertices into a primitive. View frustum clipping is performed subsequent to vertex program execution. Clip planes are not supported in the VP1 execution environment. Clip planes are supported indirectly via the clip distance (o[CLPx]) registers in the VP2 execution environment. Section 2.14.1.8, Vertex Program Specification Vertex programs are specified as an array of ubytes. The array is a string of ASCII characters encoding the program. The command LoadProgramNV(enum target, uint id, sizei len, const ubyte *program); loads a vertex program when the target parameter is VERTEX_PROGRAM_NV. Multiple programs can be loaded with different names. id names the program to load. The name space for programs is the positive integers (zero is reserved). The error INVALID_VALUE occurs if a program is loaded with an id of zero. The error INVALID_OPERATION is generated if a program is loaded for an id that is currently loaded with a program of a different program target. Managing the program name space and binding to vertex programs is discussed later in section 2.14.1.8. program is a pointer to an array of ubytes that represents the program being loaded. The length of the array is indicated by len. A second program target type known as vertex state programs is discussed in 2.14.4. At program load time, the program is parsed into a set of tokens possibly separated by white space. Spaces, tabs, newlines, carriage returns, and comments are considered whitespace. Comments begin with the character "#" and are terminated by a newline, a carriage return, or the end of the program array. The Backus-Naur Form (BNF) grammar below specifies the syntactically valid sequences for several types of vertex programs. The set of valid tokens can be inferred from the grammar. The token "" represents an empty string and is used to indicate optional rules. A program is invalid if it contains any undefined tokens or characters. The grammar provides for three different vertex program types, corresponding to the three vertex program execution environments. VP1, VP1.1, and VP2 programs match the grammar rules <vp1-program>, <vp11-program>, and <vp2-program>, respectively. Some grammar rules correspond to features or instruction forms available only in certain execution environments. Rules beginning with the prefix "vp1-" are available only to VP1 and VP1.1 programs. Rules beginning with the prefixes "vp11-" and "vp2-" are available only to VP1.1 and VP2 programs, respectively. <program> ::= <vp1-program> | <vp11-program> | <vp2-program> <vp1-program> ::= "!!VP1.0" <programBody> "END" <vp11-program> ::= "!!VP1.1" <programBody> "END" <vp2-program> ::= "!!VP2.0" <programBody> "END" <programBody> ::= <optionSequence> <programText> <optionSequence> ::= <option> <optionSequence> | "" <option> ::= "OPTION" <vp11-option> ";" | "OPTION" <vp2-option> ";" <vp11-option> ::= "NV_position_invariant" <vp2-option> ::= "NV_position_invariant" <programText> ::= <programTextItem> <programText> | "" <programTextItem> ::= <instruction> ";" | <vp2-instructionLabel> <instruction> ::= <ARL-instruction> | <VECTORop-instruction> | <SCALARop-instruction> | <BINop-instruction> | <TRIop-instruction> | <vp2-BRA-instruction> | <vp2-RET-instruction> | <vp2-ARA-instruction> <ARL-instruction> ::= <vp1-ARL-instruction> | <vp2-ARL-instruction> <vp1-ARL-instruction> ::= "ARL" <maskedAddrReg> "," <scalarSrc> <vp2-ARL-instruction> ::= <vp2-ARLop> <maskedAddrReg> "," <vectorSrc> <vp2-ARLop> ::= "ARL" | "ARLC" | "ARR" | "ARRC" <VECTORop-instruction> ::= <VECTORop> <maskedDstReg> "," <vectorSrc> <VECTORop> ::= "LIT" | "MOV" | <vp11-VECTORop> | <vp2-VECTORop> <vp11-VECTORop> ::= "ABS" <vp2-VECTORop> ::= "ABSC" | "FLR" | "FLRC" | "FRC" | "FRCC" | "LITC" | "MOVC" | "SSG" | "SSGC" <SCALARop-instruction> ::= <SCALARop> <maskedDstReg> "," <scalarSrc> <SCALARop> ::= "EXP" | "LOG" | "RCP" | "RSQ" | <vp11-SCALARop> | <vp2-SCALARop> <vp11-SCALARop> ::= "RCC" <vp2-SCALARop> ::= "COS" | "COSC" | "EX2" | "EX2C" | "LG2" | "LG2C" | "EXPC" | "LOGC" | "RCCC" | "RCPC" | "RSQC" | "SIN" | "SINC" <BINop-instruction> ::= <BINop> <maskedDstReg> "," <vectorSrc> "," <vectorSrc> <BINop> ::= "ADD" | "DP3" | "DP4" | "DST" | "MAX" | "MIN" | "MUL" | "SGE" | "SLT" | <vp11-BINop> | <vp2-BINop> <vp11-BINop> ::= "DPH" | "SUB" <vp2-BINop> ::= "ADDC" | "DP3C" | "DP4C" | "DPHC" | "DSTC" | "MAXC" | "MINC" | "MULC" | "SEQ" | "SEQC" | "SFL" | "SFLC" | "SGEC" | "SGT" | "SGTC" | "SLTC" | "SLE" | "SLEC" | "SNE" | "SNEC" | "STR" | "STRC" | "SUBC" <TRIop-instruction> ::= <TRIop> <maskedDstReg> "," <vectorSrc> "," <vectorSrc> "," <vectorSrc> <TRIop> ::= "MAD" | <vp2-TRIop> <vp2-TRIop> ::= "MADC" <vp2-BRA-instruction> ::= <vp2-BRANCHop> <vp2-branchLabel> <vp2-branchCondition> <vp2-BRANCHop> ::= "BRA" | "CAL" <vp2-RET-instruction> ::= "RET" <vp2-branchCondition> <vp2-ARA-instruction> ::= <vp2-ARAop> <maskedAddrReg> "," <addrRegister> <vp2-ARAop> ::= "ARA" | "ARAC" <scalarSrc> ::= <baseScalarSrc> | <vp2-absScalarSrc> <vp2-absScalarSrc> ::= <optionalSign> "|" <baseScalarSrc> "|" <baseScalarSrc> ::= <optionalSign> <srcRegister> <scalarSuffix> <vectorSrc> ::= <baseVectorSrc> | <vp2-absVectorSrc> <vp2-absVectorSrc> ::= <optionalSign> "|" <baseVectorSrc> "|" <baseVectorSrc> ::= <optionalSign> <srcRegister> <swizzleSuffix> <srcRegister> ::= <vtxAttribRegister> | <progParamRegister> | <tempRegister> <maskedDstReg> ::= <dstRegister> <optionalWriteMask> <optionalCCMask> <dstRegister> ::= <vtxResultRegister> | <tempRegister> | <vp2-nullRegister> <vp2-nullRegister> ::= "CC" <vp2-branchCondition> ::= <optionalCCMask> <vtxAttribRegister> ::= "v" "[" vtxAttribRegNum "]" <vtxAttribRegNum> ::= decimal integer from 0 to 15 inclusive | "OPOS" | "WGHT" | "NRML" | "COL0" | "COL1" | "FOGC" | "TEX0" | "TEX1" | "TEX2" | "TEX3" | "TEX4" | "TEX5" | "TEX6" | "TEX7" <progParamRegister> ::= <absProgParamReg> | <relProgParamReg> <absProgParamReg> ::= "c" "[" <progParamRegNum> "]" <progParamRegNum> ::= <vp1-progParamRegNum> | <vp2-progParamRegNum> <vp1-progParamRegNum> ::= decimal integer from 0 to 95 inclusive <vp2-progParamRegNum> ::= decimal integer from 0 to 255 inclusive <relProgParamReg> ::= "c" "[" <scalarAddr> <relProgParamOffset> "]" <relProgParamOffset> ::= "" | "+" <progParamPosOffset> | "-" <progParamNegOffset> <progParamPosOffset> ::= <vp1-progParamPosOff> | <vp2-progParamPosOff> <vp1-progParamPosOff> ::= decimal integer from 0 to 63 inclusive <vp2-progParamPosOff> ::= decimal integer from 0 to 255 inclusive <progParamNegOffset> ::= <vp1-progParamNegOff> | <vp2-progParamNegOff> <vp1-progParamNegOff> ::= decimal integer from 0 to 64 inclusive <vp2-progParamNegOff> ::= decimal integer from 0 to 256 inclusive <tempRegister> ::= "R0" | "R1" | "R2" | "R3" | "R4" | "R5" | "R6" | "R7" | "R8" | "R9" | "R10" | "R11" <vp2-tempRegister> ::= "R12" | "R13" | "R14" | "R15" <vtxResultRegister> ::= "o" "[" <vtxResultRegName> "]" <vtxResultRegName> ::= "HPOS" | "COL0" | "COL1" | "BFC0" | "BFC1" | "FOGC" | "PSIZ" | "TEX0" | "TEX1" | "TEX2" | "TEX3" | "TEX4" | "TEX5" | "TEX6" | "TEX7" | <vp2-resultRegName> <vp2-resultRegName> ::= "CLP0" | "CLP1" | "CLP2" | "CLP3" | "CLP4" | "CLP5" <scalarAddr> ::= <addrRegister> "." <addrRegisterComp> <maskedAddrReg> ::= <addrRegister> <addrWriteMask> <addrRegister> ::= "A0" | <vp2-addrRegister> <vp2-addrRegister> ::= "A1" <addrRegisterComp> ::= "x" | <vp2-addrRegisterComp> <vp2-addrRegisterComp> ::= "y" | "z" | "w" <addrWriteMask> ::= "." "x" | <vp2-addrWriteMask> <vp2-addrWriteMask> ::= "" | "." "y" | "." "x" "y" | "." "z" | "." "x" "z" | "." "y" "z" | "." "x" "y" "z" | "." "w" | "." "x" "w" | "." "y" "w" | "." "x" "y" "w" | "." "z" "w" | "." "x" "z" "w" | "." "y" "z" "w" | "." "x" "y" "z" "w" <optionalSign> ::= "" | "-" | <vp2-optionalSign> <vp2-optionalSign> ::= "+" <vp2-instructionLabel> ::= <vp2-branchLabel> ":" <vp2-branchLabel> ::= <identifier> <optionalWriteMask> ::= "" | "." "x" | "." "y" | "." "x" "y" | "." "z" | "." "x" "z" | "." "y" "z" | "." "x" "y" "z" | "." "w" | "." "x" "w" | "." "y" "w" | "." "x" "y" "w" | "." "z" "w" | "." "x" "z" "w" | "." "y" "z" "w" | "." "x" "y" "z" "w" <optionalCCMask> ::= "" | <vp2-ccMask> <vp2-ccMask> ::= "(" <vp2-ccMaskRule> <swizzleSuffix> ")" <vp2-ccMaskRule> ::= "EQ" | "GE" | "GT" | "LE" | "LT" | "NE" | "TR" | "FL" <scalarSuffix> ::= "." <component> <swizzleSuffix> ::= "" | "." <component> | "." <component> <component> <component> <component> <component> ::= "x" | "y" | "z" | "w" The <identifier> rule matches a sequence of one or more letters ("A" through "Z", "a" through "z", and "_") and digits ("0" through "9); the first character must be a letter. The underscore ("_") counts as a letter. Upper and lower case letters are different (names are case-sensitive). The <vertexAttribRegNum> rule matches both register numbers 0 through 15 and a set of mnemonics that abbreviate the aliasing of conventional per-vertex parameters to vertex attribute register numbers. Table X.3 shows the mapping from mnemonic to vertex attribute register number and what the mnemonic abbreviates. Vertex Attribute Mnemonic Register Number Meaning -------- ---------------- -------------------- "OPOS" 0 object position "WGHT" 1 vertex weight "NRML" 2 normal "COL0" 3 primary color "COL1" 4 secondary color "FOGC" 5 fog coordinate "TEX0" 8 texture coordinate 0 "TEX1" 9 texture coordinate 1 "TEX2" 10 texture coordinate 2 "TEX3" 11 texture coordinate 3 "TEX4" 12 texture coordinate 4 "TEX5" 13 texture coordinate 5 "TEX6" 14 texture coordinate 6 "TEX7" 15 texture coordinate 7 Table X.3: The mapping between vertex attribute register numbers, mnemonics, and meanings. A vertex program fails to load if it does not write at least one component of the HPOS register. A vertex program fails to load in the VP1 execution environment if it contains more than 128 instructions. A vertex program fails to load in the VP2 execution environment if it contains more than 256 instructions. Each block of text matching the <instruction> rule counts as an instruction. A vertex program fails to load if any instruction sources more than one unique program parameter register. An instruction can match the <progParamRegister> rule more than once only if all such matches are identical. A vertex program fails to load if any instruction sources more than one unique vertex attribute register. An instruction can match the <vtxAttribRegister> rule more than once only if all such matches refer to the same register. The error INVALID_OPERATION is generated if a vertex program fails to load because it is not syntactically correct or for one of the semantic restrictions listed above. The error INVALID_OPERATION is generated if a program is loaded for id when id is currently loaded with a program of a different target. A successfully loaded vertex program is parsed into a sequence of instructions. Each instruction is identified by its tokenized name. The operation of these instructions when executed is defined in section 2.14.1.10. A successfully loaded program replaces the program previously assigned to the name specified by id. If the OUT_OF_MEMORY error is generated by LoadProgramNV, no change is made to the previous contents of the named program. Querying the value of PROGRAM_ERROR_POSITION_NV returns a ubyte offset into the last loaded program string indicating where the first error in the program. If the program fails to load because of a semantic restriction that cannot be determined until the program is fully scanned, the error position will be len, the length of the program. If the program loads successfully, the value of PROGRAM_ERROR_POSITION_NV is assigned the value negative one. Section 2.14.1.9, Vertex Program Binding and Program Management The current vertex program is invoked whenever vertex attribute zero is updated (whether by a VertexAttributeNV or Vertex command). The current vertex program is updated by BindProgramNV(enum target, uint id); where target must be VERTEX_PROGRAM_NV. This binds the vertex program named by id as the current vertex program. The error INVALID_OPERATION is generated if id names a program that is not a vertex program (for example, if id names a vertex state program as described in section 2.14.4). Binding to a nonexistent program id does not generate an error. In particular, binding to program id zero does not generate an error. However, because program zero cannot be loaded, program zero is always nonexistent. If a program id is successfully loaded with a new vertex program and id is also the currently bound vertex program, the new program is considered the currently bound vertex program. The INVALID_OPERATION error is generated when both vertex program mode is enabled and Begin is called (or when a command that performs an implicit Begin is called) if the current vertex program is nonexistent or not valid. A vertex program may not be valid for reasons explained in section 2.14.5. Programs are deleted by calling void DeleteProgramsNV(sizei n, const uint *ids); ids contains n names of programs to be deleted. After a program is deleted, it becomes nonexistent, and its name is again unused. If a program that is currently bound is deleted, it is as though BindProgramNV has been executed with the same target as the deleted program and program zero. Unused names in ids are silently ignored, as is the value zero. The command void GenProgramsNV(sizei n, uint *ids); returns n previously unused program names in ids. These names are marked as used, for the purposes of GenProgramsNV only, but they become existent programs only when the are first loaded using LoadProgramNV. The error INVALID_VALUE is generated if n is negative. An implementation may choose to establish a working set of programs on which binding and ExecuteProgramNV operations (execute programs are explained in section 2.14.4) are performed with higher performance. A program that is currently part of this working set is said to be resident. The command boolean AreProgramsResidentNV(sizei n, const uint *ids, boolean *residences); returns TRUE if all of the n programs named in ids are resident, or if the implementation does not distinguish a working set. If at least one of the programs named in ids is not resident, then FALSE is returned, and the residence of each program is returned in residences. Otherwise the contents of residences are not changed. If any of the names in ids are nonexistent or zero, FALSE is returned, the error INVALID_VALUE is generated, and the contents of residences are indeterminate. The residence status of a single named program can also be queried by calling GetProgramivNV with id set to the name of the program and pname set to PROGRAM_RESIDENT_NV. AreProgramsResidentNV indicates only whether a program is currently resident, not whether it could not be made resident. An implementation may choose to make a program resident only on first use, for example. The client may guide the GL implementation in determining which programs should be resident by requesting a set of programs to make resident. The command void RequestResidentProgramsNV(sizei n, const uint *ids); requests that the n programs named in ids should be made resident. While all the programs are not guaranteed to become resident, the implementation should make a best effort to make as many of the programs resident as possible. As a result of making the requested programs resident, program names not among the requested programs may become non-resident. Higher priority for residency should be given to programs listed earlier in the ids array. RequestResidentProgramsNV silently ignores attempts to make resident nonexistent program names or zero. AreProgramsResidentNV can be called after RequestResidentProgramsNV to determine which programs actually became resident. Section 2.14.2, Vertex Program Operation In the VP1 execution environment, there are twenty-one vertex program instructions. Four instructions (ABS, DPH, RCC, and SUB) are available only in the VP1.1 execution environment. The instructions and their respective input and output parameters are summarized in Table X.4. Instruction Inputs Output Description ----------- ------ ------ -------------------------------- ABS(*) v v absolute value ADD v,v v add ARL v as address register load DP3 v,v ssss 3-component dot product DP4 v,v ssss 4-component dot product DPH(*) v,v ssss homogeneous dot product DST v,v v distance vector EXP s v exponential base 2 (approximate) LIT v v compute light coefficients LOG s v logarithm base 2 (approximate) MAD v,v,v v multiply and add MAX v,v v maximum MIN v,v v minimum MOV v v move MUL v,v v multiply RCC(*) s ssss reciprocal (clamped) RCP s ssss reciprocal RSQ s ssss reciprocal square root SGE v,v v set on greater than or equal SLT v,v v set on less than SUB(*) v,v v subtract Table X.4: Summary of vertex program instructions in the VP1 execution environment. "v" indicates a floating-point vector input or output, "s" indicates a floating-point scalar input, "ssss" indicates a scalar output replicated across a 4-component vector, "as" indicates a single component of an address register. In the VP2 execution environment, are thirty-nine vertex program instructions. Vertex program instructions may have an optional suffix of "C" to allow an update of the condition code register (section 2.14.1.6). For example, there are two instructions to perform vector addition, "ADD" and "ADDC". The vertex program instructions available in the VP2 execution environment and their respective input and output parameters are summarized in Table X.5. Instruction Inputs Output Description ----------- ------ ------ -------------------------------- ABS[C] v v absolute value ADD[C] v,v v add ARA[C] av av address register add ARL[C] v av address register load ARR[C] v av address register load (with round) BRA as none branch CAL as none subroutine call COS[C] s ssss cosine DP3[C] v,v ssss 3-component dot product DP4[C] v,v ssss 4-component dot product DPH[C] v,v ssss homogeneous dot product DST[C] v,v v distance vector EX2[C] s ssss exponential base 2 EXP[C] s v exponential base 2 (approximate) FLR[C] v v floor FRC[C] v v fraction LG2[C] s ssss logarithm base 2 LIT[C] v v compute light coefficients LOG[C] s v logarithm base 2 (approximate) MAD[C] v,v,v v multiply and add MAX[C] v,v v maximum MIN[C] v,v v minimum MOV[C] v v move MUL[C] v,v v multiply RCC[C] s ssss reciprocal (clamped) RCP[C] s ssss reciprocal RET none none subroutine call return RSQ[C] s ssss reciprocal square root SEQ[C] v,v v set on equal SFL[C] v,v v set on false SGE[C] v,v v set on greater than or equal SGT[C] v,v v set on greater than SIN[C] s ssss sine SLE[C] v,v v set on less than or equal SLT[C] v,v v set on less than SNE[C] v,v v set on not equal SSG[C] v v set sign STR[C] v,v v set on true SUB[C] v,v v subtract Table X.5: Summary of vertex program instructions in the VP2 execution environment. "v" indicates a floating-point vector input or output, "s" indicates a floating-point scalar input, "ssss" indicates a scalar output replicated across a 4-component vector, "av" indicates a full address register, "as" indicates a single component of an address register. Section 2.14.2.1, Vertex Program Operands Most vertex program instructions operate on floating-point vectors, floating-point scalars, or integer scalars as, indicated in the grammar (see section 2.14.1.8) by the rules <vectorSrc>, <scalarSrc>, and <scalarAddr>, respectively. The basic set of floating-point scalar operands is defined by the grammar rule <baseScalarSrc>. Scalar operands are single components of vertex attribute, program parameter, or temporary registers, as allowed by the <srcRegister> rule. A vector component is selected by the <scalarSuffix> rule, where the characters "x", "y", "z", and "w" select the x, y, z, and w components, respectively, of the vector. The basic set of floating-point vector operands is defined by the grammar rule <baseVectorSrc>. Vector operands can be obtained from vertex attribute, program parameter, or temporary registers as allowed by the <srcRegister> rule. Basic vector operands can be swizzled according to the <swizzleSuffix> rule. In its most general form, the <swizzleSuffix> rule matches the pattern ".????" where each question mark is replaced with one of "x", "y", "z", or "w". For such patterns, the x, y, z, and w components of the operand are taken from the vector components named by the first, second, third, and fourth character of the pattern, respectively. For example, if the swizzle suffix is ".yzzx" and the specified source contains {2,8,9,0}, the swizzled operand used by the instruction is {8,9,9,2}. If the <swizzleSuffix> rule matches "", it is treated as though it were ".xyzw". If the <swizzleSuffix> rule matches (ignoring whitespace) ".x", ".y", ".z", or ".w", these are treated the same as ".xxxx", ".yyyy", ".zzzz", and ".wwww" respectively. Floating-point scalar or vector operands can optionally be negated according to the <negate> rules in <baseScalarSrc> and <baseVectorSrc>. If the <negate> matches "-", each operand or operand component is negated. In the VP2 execution environment, a component-wise absolute value operation is performed on an operand if the <scalarSrc> or <vectorSrc> rules match <vp2-absScalarSrc> or <vp2-absVectorSrc>. In this case, the absolute value of each component of the operand is taken. In addition, if the <negate> rule in <vp2-absScalarSrc> or <vp2-absVectorSrc> matches "-", each component is subsequently negated. Integer scalar operands are single components of one of the address register vectors, as identified by the <addrRegister> rule. A vector component is selected by the <scalarSuffix> rule in the same manner as floating-point scalar operands. Negation and absolute value operations are not available for integer scalar operands. The following pseudo-code spells out the operand generation process. In the pseudo-code, "float" and "int" are floating-point and integer scalar types, while "floatVec" and "intVec" are four-component vectors. "source" is the register used for the operand, matching the <srcRegister> or <addrRegister> rules. "absolute" is TRUE if the operand matches the <vp2-absScalarSrc> or <vp2-absVectorSrc> rules, and FALSE otherwise. "negateBase" is TRUE if the <negate> rule in <baseScalarSrc> or <baseVectorSrc> matches "-" and FALSE otherwise. "negateAbs" is TRUE if the <negate> rule in <vp2-absScalarSrc> or <vp2-absVectorSrc> matches "-" and FALSE otherwise. The ".c***", ".*c**", ".**c*", ".***c" modifiers refer to the x, y, z, and w components obtained by the swizzle operation. floatVec VectorLoad(floatVec source) { floatVec operand; operand.x = source.c***; operand.y = source.*c**; operand.z = source.**c*; operand.w = source.***c; if (negateBase) { operand.x = -operand.x; operand.y = -operand.y; operand.z = -operand.z; operand.w = -operand.w; } if (absolute) { operand.x = abs(operand.x); operand.y = abs(operand.y); operand.z = abs(operand.z); operand.w = abs(operand.w); } if (negateAbs) { operand.x = -operand.x; operand.y = -operand.y; operand.z = -operand.z; operand.w = -operand.w; } return operand; } float ScalarLoad(floatVec source) { float operand; operand = source.c***; if (negateBase) { operand = -operand; } if (absolute) { operand = abs(operand); } if (negateAbs) { operand = -operand; } return operand; } intVec AddrVectorLoad(intVec addrReg) { intVec operand; operand.x = source.c***; operand.y = source.*c**; operand.z = source.**c*; operand.w = source.***c; return operand; } int AddrScalarLoad(intVec addrReg) { return source.c***; } If an operand is obtained from a program parameter register, by matching the <progParamRegister> rule, the register number can be obtained by absolute or relative addressing. When absolute addressing is used, by matching the <absProgParamReg> rule, the program parameter register number is the number matching the <progParamRegNum>. When relative addressing is used, by matching the <relProgParamReg> rule, the program parameter register number is computed during program execution. An index is computed by adding the integer scalar operand specified by the <scalarAddr> rule to the positive or negative offset specified by the <progParamOffset> rule. If <progParamOffset> matches "", an offset of zero is used. The following pseudo-code spells out the process of loading a program parameter. "addrReg" refers to the address register used for relative addressing, "absolute" is TRUE if the operand uses absolute addressing and FALSE otherwise. "paramNumber" is the program parameter number for absolute addressing; "paramOffset" is the program parameter offset for relative addressing. "paramRegiser" is an array holding the complete set of program parameter registers. floatVec ProgramParameterLoad(intVec addrReg) { int index; if (absolute) { index = paramNumber; } else { index = AddrScalarLoad(addrReg) + paramOffset } return paramRegister[index]; } Section 2.14.2.2, Vertex Program Destination Register Update Most vertex program instructions write a 4-component result vector to a single temporary, vertex result, or address register. Writes to individual components of the destination register are controlled by individual component write masks specified as part of the instruction. In the VP2 execution environment, writes are additionally controlled by the a condition code write mask, which is computed at run time. The component write mask is specified by the <optionalWriteMask> rule found in the <maskedDstReg> or <maskedAddrReg> rule. If the optional mask is "", all components are enabled. Otherwise, the optional mask names the individual components to enable. The characters "x", "y", "z", and "w" match the x, y, z, and w components respectively. For example, an optional mask of ".xzw" indicates that the x, z, and w components should be enabled for writing but the y component should not. The grammar requires that the destination register mask components must be listed in "xyzw" order. In the VP2 execution environment, the condition code write mask is specified by the <optionalCCMask> rule found in the <maskedDstReg> and <maskedAddrReg> rules. If the condition code mask matches "", all components are enabled. Otherwise, the condition code register is loaded and swizzled according to the swizzle codes specified by <swizzleSuffix>. Each component of the swizzled condition code is tested according to the rule given by <ccMaskRule>. <ccMaskRule> may have the values "EQ", "NE", "LT", "GE", LE", or "GT", which mean to enable writes if the corresponding condition code field evaluates to equal, not equal, less than, greater than or equal, less than or equal, or greater than, respectively. Comparisons involving condition codes of "UN" (unordered) evaluate to true for "NE" and false otherwise. For example, if the condition code is (GT,LT,EQ,GT) and the condition code mask is "(NE.zyxw)", the swizzle operation will load (EQ,LT,GT,GT) and the mask will thus will enable writes on the y, z, and w components. In addition, "TR" always enables writes and "FL" always disables writes, regardless of the condition code. Each component of the destination register is updated with the result of the vertex program instruction if and only if the component is enabled for writes by the component write mask, and the optional condition code mask (if applicable). Otherwise, the component of the destination register remains unchanged. In the VP2 execution environment, a vertex program instruction can also optionally update the condition code register. The condition code is updated if the condition code register update suffix "C" is present in the instruction. The instruction "ADDC" will update the condition code; the otherwise equivalent instruction "ADD" will not. If condition code updates are enabled, each component of the destination register enabled for writes is compared to zero. The corresponding component of the condition code is set to "LT", "EQ", or "GT", if the written component is less than, equal to, or greater than zero, respectively. Condition code components are set to "UN" if the written component is NaN. Values of -0.0 and +0.0 both evaluate to "EQ". If a component of the destination register is not enabled for writes, the corresponding condition code component is also unchanged. In the following example code, # R1=(-2, 0, 2, NaN) R0 CC MOVC R0, R1; # ( -2, 0, 2, NaN) (LT,EQ,GT,UN) MOVC R0.xyz, R1.yzwx; # ( 0, 2, NaN, NaN) (EQ,GT,UN,UN) MOVC R0 (NE), R1.zywx; # ( 0, 0, NaN, -2) (EQ,EQ,UN,LT) the first instruction writes (-2,0,2,NaN) to R0 and updates the condition code to (LT,EQ,GT,UN). The second instruction, only the "x", "y", and "z" components of R0 and the condition code are updated, so R0 ends up with (0,2,NaN,NaN) and the condition code ends up with (EQ,GT,UN,UN). In the third instruction, the condition code mask disables writes to the x component (its condition code field is "EQ"), so R0 ends up with (0,0,NaN,-2) and the condition code ends up with (EQ,EQ,UN,LT). The following pseudocode illustrates the process of writing a result vector to the destination register. In the pseudocode, "instrmask" refers to the component write mask given by the <optionalWriteMask> rule. In the VP1 execution environment, "ccMaskRule" is always "" and "updatecc" is always FALSE. In the VP2 execution environment, "ccMaskRule" refers to the condition code mask rule given by <vp2-optionalCCMask> and "updatecc" is TRUE if and only if condition code updates are enabled. "result", "destination", and "cc" refer to the result vector, the register selected by <dstRegister> and the condition code, respectively. Condition codes do not exist in the VP1 execution environment. boolean TestCC(CondCode field) { switch (ccMaskRule) { case "EQ": return (field == "EQ"); case "NE": return (field != "EQ"); case "LT": return (field == "LT"); case "GE": return (field == "GT" || field == "EQ"); case "LE": return (field == "LT" || field == "EQ"); case "GT": return (field == "GT"); case "TR": return TRUE; case "FL": return FALSE; case "": return TRUE; } } enum GenerateCC(float value) { if (value == NaN) { return UN; } else if (value < 0) { return LT; } else if (value == 0) { return EQ; } else { return GT; } } void UpdateDestination(floatVec destination, floatVec result) { floatVec merged; ccVec mergedCC; // Merge the converted result into the destination register, under // control of the compile- and run-time write masks. merged = destination; mergedCC = cc; if (instrMask.x && TestCC(cc.c***)) { merged.x = result.x; if (updatecc) mergedCC.x = GenerateCC(result.x); } if (instrMask.y && TestCC(cc.*c**)) { merged.y = result.y; if (updatecc) mergedCC.y = GenerateCC(result.y); } if (instrMask.z && TestCC(cc.**c*)) { merged.z = result.z; if (updatecc) mergedCC.z = GenerateCC(result.z); } if (instrMask.w && TestCC(cc.***c)) { merged.w = result.w; if (updatecc) mergedCC.w = GenerateCC(result.w); } // Write out the new destination register and condition code. destination = merged; cc = mergedCC; } Section 2.14.2.3, Vertex Program Execution In the VP1 execution environment, vertex programs consist of a sequence of instructions without no support for branching. Vertex programs begin by executing the first instruction in the program, and execute instructions in the order specified in the program until the last instruction is reached. VP2 vertex programs can contain one or more instruction labels, matching the grammar rule <vp2-instructionLabel>. An instruction label can be referred to explicitly in branch (BRA) or subroutine call (CAL) instructions. Instruction labels can be defined or used at any point in the body of a program, and can be used in instructions before being defined in the program string. VP2 vertex program branching instructions can be conditional. The branch condition is specified by the <vp2-conditionMask> and may depend on the contents of the condition code register. Branch conditions are evaluated by evaluating a condition code write mask in exactly the same manner as done for register writes (section 2.14.2.2). If any of the four components of the condition code write mask are enabled, the branch is taken and execution continues with the instruction following the label specified in the instruction. Otherwise, the instruction is ignored and vertex program execution continues with the next instruction. In the following example code, MOVC CC, c[0]; # c[0]=(-2, 0, 2, NaN), CC gets (LT,EQ,GT,UN) BRA label1 (LT.xyzw); MOV R0,R1; # not executed label1: BRA label2 (LT.wyzw); MOV R0,R2; # executed label2: the first BRA instruction loads a condition code of (LT,EQ,GT,UN) while the second BRA instruction loads a condition code of (UN,EQ,GT,UN). The first branch will be taken because the "x" component evaluates to LT; the second branch will not be taken because no component evaluates to LT. VP2 vertex programs can specify subroutine calls. When a subroutine call (CAL) instruction is executed, a reference to the instruction immediately following the CAL instruction is pushed onto the call stack. When a subroutine return (RET) instruction is executed, an instruction reference is popped off the call stack and program execution continues with the popped instruction. A vertex program will terminate if a CAL instruction is executed with four entries already in the call stack or if a RET instruction is executed with an empty call stack. If a VP2 vertex program has an instruction label "main", program execution begins with the instruction immediately following the instruction label. Otherwise, program execution begins with the first instruction of the program. Instructions will be executed sequentially in the order specified in the program, although branch instructions will affect the instruction execution order, as described above. A vertex program will terminate after executing a RET instruction with an empty call stack. A vertex program will also terminate after executing the last instruction in the program, unless that instruction was a taken branch. A vertex program will fail to load if an instruction refers to a label that is not defined in the program string. A vertex program will terminate abnormally if a subroutine call instruction produces a call stack overflow. Additionally, a vertex program will terminate abnormally after executing 65536 instructions to prevent hangs caused by infinite loops in the program. When a vertex program terminates, normally or abnormally, it will emit a vertex whose attributes are taken from the final values of the vertex result registers (section 2.14.1.5). Section 2.14.3, Vertex Program Instruction Set The following sections describe the set of supported vertex program instructions. Instructions available only in the VP1.1 or VP2 execution environment will be noted in the instruction description. Each section will contain pseudocode describing the instruction. Instructions will have up to three operands, referred to as "op0", "op1", and "op2". The operands are loaded using the mechanisms specified in section 2.14.2.1. Most instructions will generate a result vector called "result". The result vector is then written to the destination register specified in the instruction using the mechanisms specified in section 2.14.2.2. Operands and results are represented as 32-bit single-precision floating-point numbers according to the IEEE 754 floating-point specification. IEEE denorm encodings, used to represent numbers smaller than 2^-126, are not supported. All such numbers are flushed to zero. There are three special encodings referred to in this section: +INF means "positive infinity", -INF means "negative infinity", and NaN refers to "not a number". Arithmetic operations are typically carried out in single precision according to the rules specified in the IEEE 754 specification. Any exceptions and special cases will be noted in the instruction description. Section 2.14.3.1, ABS: Absolute Value The ABS instruction performs a component-wise absolute value operation on the single operand to yield a result vector. tmp = VectorLoad(op0); result.x = abs(tmp.x); result.y = abs(tmp.y); result.z = abs(tmp.z); result.w = abs(tmp.w); The following special-case rules apply to absolute value operation: 1. abs(NaN) = NaN. 2. abs(-INF) = abs(+INF) = +INF. 3. abs(-0.0) = abs(+0.0) = +0.0. The ABS instruction is available only in the VP1.1 and VP2 execution environments. In the VP1.0 execution environment, the same functionality can be achieved with "MAX result, src, -src". In the VP2 execution environment, the ABS instruction is effectively obsolete, since instructions can take the absolute value of each operand at no cost. Section 2.14.3.2, ADD: Add The ADD instruction performs a component-wise add of the two operands to yield a result vector. tmp0 = VectorLoad(op0); tmp1 = VectorLoad(op1); result.x = tmp0.x + tmp1.x; result.y = tmp0.y + tmp1.y; result.z = tmp0.z + tmp1.z; result.w = tmp0.w + tmp1.w; The following special-case rules apply to addition: 1. "A+B" is always equivalent to "B+A". 2. NaN + <x> = NaN, for all <x>. 3. +INF + <x> = +INF, for all <x> except NaN and -INF. 4. -INF + <x> = -INF, for all <x> except NaN and +INF. 5. +INF + -INF = NaN. 6. -0.0 + <x> = <x>, for all <x>. 7. +0.0 + <x> = <x>, for all <x> except -0.0. Section 2.14.3.3, ARA: Address Register Add The ARA instruction adds two pairs of components of a vector address register operand to produce an integer result vector. The "x" and "z" components of the result vector contain the sum of the "x" and "z" components of the operand; the "y" and "w" components of the result vector contain the sum of the "y" and "w" components of the operand. Each component of the result vector is clamped to [-512, +511], the range of representable address register components. itmp = AddrVectorLoad(op0); iresult.x = itmp.x + itmp.z; iresult.y = itmp.y + itmp.w; iresult.z = itmp.x + itmp.z; iresult.w = itmp.y + itmp.w; if (iresult.x < -512) iresult.x = -512; if (iresult.x > 511) iresult.x = 511; if (iresult.y < -512) iresult.y = -512; if (iresult.y > 511) iresult.y = 511; if (iresult.z < -512) iresult.z = -512; if (iresult.z > 511) iresult.z = 511; if (iresult.w < -512) iresult.w = -512; if (iresult.w > 511) iresult.w = 511; Component swizzling is not supported when the operand is loaded. The ARA instruction is available only in the VP2 execution environment. Section 2.14.3.4, ARL: Address Register Load In the VP1 execution environment, the ARL instruction loads a single scalar operand and performs a floor operation to generate an integer scalar to be written to the address register. tmp = ScalarLoad(op0); iresult.x = floor(tmp); In the VP2 execution environment, the ARL instruction loads a single vector operand and performs a component-wise floor operation to generate an integer result vector. Each component of the result vector is clamped to [-512, +511], the range of representable address register components. The ARL instruction applies all masking operations to address register writes as are described in section 2.14.2.2. tmp = VectorLoad(op0); iresult.x = floor(tmp.x); iresult.y = floor(tmp.y); iresult.z = floor(tmp.z); iresult.w = floor(tmp.w); if (iresult.x < -512) iresult.x = -512; if (iresult.x > 511) iresult.x = 511; if (iresult.y < -512) iresult.y = -512; if (iresult.y > 511) iresult.y = 511; if (iresult.z < -512) iresult.z = -512; if (iresult.z > 511) iresult.z = 511; if (iresult.w < -512) iresult.w = -512; if (iresult.w > 511) iresult.w = 511; The following special-case rules apply to floor computation: 1. floor(NaN) = NaN. 2. floor(<x>) = <x>, for -0.0, +0.0, -INF, and +INF. In all cases, the sign of the result is equal to the sign of the operand. Section 2.14.3.5, ARR: Address Register Load (with round) The ARR instruction loads a single vector operand and performs a component-wise round operation to generate an integer result vector. Each component of the result vector is clamped to [-512, +511], the range of representable address register components. The ARR instruction applies all masking operations to address register writes as described in section 2.14.2.2. tmp = VectorLoad(op0); iresult.x = round(tmp.x); iresult.y = round(tmp.y); iresult.z = round(tmp.z); iresult.w = round(tmp.w); if (iresult.x < -512) iresult.x = -512; if (iresult.x > 511) iresult.x = 511; if (iresult.y < -512) iresult.y = -512; if (iresult.y > 511) iresult.y = 511; if (iresult.z < -512) iresult.z = -512; if (iresult.z > 511) iresult.z = 511; if (iresult.w < -512) iresult.w = -512; if (iresult.w > 511) iresult.w = 511; The rounding function, round(x), returns the nearest integer to <x>. If the fractional portion of <x> is 0.5, round(x) selects the nearest even integer. The ARR instruction is available only in the VP2 execution environment. Section 2.14.3.6, BRA: Branch The BRA instruction conditionally transfers control to the instruction following the label specified in the instruction. The following pseudocode describes the operation of the instruction: if (TestCC(cc.c***) || TestCC(cc.*c**) || TestCC(cc.**c*) || TestCC(cc.***c)) { // continue execution at instruction following <branchLabel> } else { // do nothing } In the pseudocode, <branchLabel> is the label specified in the instruction matching the <vp2-branchLabel> grammar rule. The BRA instruction is available only in the VP2 execution environment. Section 2.14.3.7, CAL: Subroutine Call The CAL instruction conditionally transfers control to the instruction following the label specified in the instruction. It also pushes a reference to the instruction immediately following the CAL instruction onto the call stack, where execution will continue after executing the matching RET instruction. The following pseudocode describes the operation of the instruction: if (TestCC(cc.c***) || TestCC(cc.*c**) || TestCC(cc.**c*) || TestCC(cc.***c)) { if (callStackDepth >= 4) { // terminate vertex program } else { callStack[callStackDepth] = nextInstruction; callStackDepth++; } // continue execution at instruction following <branchLabel> } else { // do nothing } In the pseudocode, <branchLabel> is the label specified in the instruction matching the <vp2-branchLabel> grammar rule, <callStackDepth> is the current depth of the call stack, <callStack> is an array holding the call stack, and <nextInstruction> is a reference to the instruction immediately following the present one in the program string. The CAL instruction is available only in the VP2 execution environment. Section 2.14.3.8, COS: Cosine The COS instruction approximates the cosine of the angle specified by the scalar operand and replicates the approximation to all four components of the result vector. The angle is specified in radians and does not have to be in the range [0,2*PI]. tmp = ScalarLoad(op0); result.x = ApproxCosine(tmp); result.y = ApproxCosine(tmp); result.z = ApproxCosine(tmp); result.w = ApproxCosine(tmp); The approximation function ApproxCosine is accurate to at least 22 bits with an angle in the range [0,2*PI]. | ApproxCosine(x) - cos(x) | < 1.0 / 2^22, if 0.0 <= x < 2.0 * PI. The error in the approximation will typically increase with the absolute value of the angle when the angle falls outside the range [0,2*PI]. The following special-case rules apply to cosine approximation: 1. ApproxCosine(NaN) = NaN. 2. ApproxCosine(+/-INF) = NaN. 3. ApproxCosine(+/-0.0) = +1.0. The COS instruction is available only in the VP2 execution environment. Section 2.14.3.9, DP3: 3-component Dot Product The DP3 instruction computes a three component dot product of the two operands (using the x, y, and z components) and replicates the dot product to all four components of the result vector. tmp0 = VectorLoad(op0); tmp1 = VectorLoad(op1): result.x = (tmp0.x * tmp1.x) + (tmp0.y * tmp1.y) + (tmp0.z * tmp1.z); result.y = (tmp0.x * tmp1.x) + (tmp0.y * tmp1.y) + (tmp0.z * tmp1.z); result.z = (tmp0.x * tmp1.x) + (tmp0.y * tmp1.y) + (tmp0.z * tmp1.z); result.w = (tmp0.x * tmp1.x) + (tmp0.y * tmp1.y) + (tmp0.z * tmp1.z); Section 2.14.3.10, DP4: 4-component Dot Product The DP4 instruction computes a four component dot product of the two operands and replicates the dot product to all four components of the result vector. tmp0 = VectorLoad(op0); tmp1 = VectorLoad(op1): result.x = (tmp0.x * tmp1.x) + (tmp0.y * tmp1.y) + (tmp0.z * tmp1.z) + (tmp0.w * tmp1.w); result.y = (tmp0.x * tmp1.x) + (tmp0.y * tmp1.y) + (tmp0.z * tmp1.z) + (tmp0.w * tmp1.w); result.z = (tmp0.x * tmp1.x) + (tmp0.y * tmp1.y) + (tmp0.z * tmp1.z) + (tmp0.w * tmp1.w); result.w = (tmp0.x * tmp1.x) + (tmp0.y * tmp1.y) + (tmp0.z * tmp1.z) + (tmp0.w * tmp1.w); Section 2.14.3.11, DPH: Homogeneous Dot Product The DPH instruction computes a four-component dot product of the two operands, except that the W component of the first operand is assumed to be 1.0. The instruction replicates the dot product to all four components of the result vector. tmp0 = VectorLoad(op0); tmp1 = VectorLoad(op1): result.x = (tmp0.x * tmp1.x) + (tmp0.y * tmp1.y) + (tmp0.z * tmp1.z) + tmp1.w; result.y = (tmp0.x * tmp1.x) + (tmp0.y * tmp1.y) + (tmp0.z * tmp1.z) + tmp1.w; result.z = (tmp0.x * tmp1.x) + (tmp0.y * tmp1.y) + (tmp0.z * tmp1.z) + tmp1.w; result.w = (tmp0.x * tmp1.x) + (tmp0.y * tmp1.y) + (tmp0.z * tmp1.z) + tmp1.w; The DPH instruction is available only in the VP1.1 and VP2 execution environments. Section 2.14.3.12, DST: Distance Vector The DST instruction computes a distance vector from two specially- formatted operands. The first operand should be of the form [NA, d^2, d^2, NA] and the second operand should be of the form [NA, 1/d, NA, 1/d], where NA values are not relevant to the calculation and d is a vector length. If both vectors satisfy these conditions, the result vector will be of the form [1.0, d, d^2, 1/d]. The exact behavior is specified in the following pseudo-code: tmp0 = VectorLoad(op0); tmp1 = VectorLoad(op1); result.x = 1.0; result.y = tmp0.y * tmp1.y; result.z = tmp0.z; result.w = tmp1.w; Given an arbitrary vector, d^2 can be obtained using the DP3 instruction (using the same vector for both operands) and 1/d can be obtained from d^2 using the RSQ instruction. This distance vector is useful for per-vertex light attenuation calculations: a DP3 operation using the distance vector and an attenuation constants vector as operands will yield the attenuation factor. Section 2.14.3.13, EX2: Exponential Base 2 The EX2 instruction approximates 2 raised to the power of the scalar operand and replicates it to all four components of the result vector. tmp = ScalarLoad(op0); result.x = Approx2ToX(tmp); result.y = Approx2ToX(tmp); result.z = Approx2ToX(tmp); result.w = Approx2ToX(tmp); The approximation function is accurate to at least 22 bits: | Approx2ToX(x) - 2^x | < 1.0 / 2^22, if 0.0 <= x < 1.0, and, in general, | Approx2ToX(x) - 2^x | < (1.0 / 2^22) * (2^floor(x)). The following special-case rules apply to exponential approximation: 1. Approx2ToX(NaN) = NaN. 2. Approx2ToX(-INF) = +0.0. 3. Approx2ToX(+INF) = +INF. 4. Approx2ToX(+/-0.0) = +1.0. The EX2 instruction is available only in the VP2 execution environment. Section 2.14.3.14, EXP: Exponential Base 2 (approximate) The EXP instruction computes a rough approximation of 2 raised to the power of the scalar operand. The approximation is returned in the "z" component of the result vector. A vertex program can also use the "x" and "y" components of the result vector to generate a more accurate approximation by evaluating result.x * f(result.y), where f(x) is a user-defined function that approximates 2^x over the domain [0.0, 1.0). The "w" component of the result vector is always 1.0. The exact behavior is specified in the following pseudo-code: tmp = ScalarLoad(op0); result.x = 2^floor(tmp); result.y = tmp - floor(tmp); result.z = RoughApprox2ToX(tmp); result.w = 1.0; The approximation function is accurate to at least 11 bits: | RoughApprox2ToX(x) - 2^x | < 1.0 / 2^11, if 0.0 <= x < 1.0, and, in general, | RoughApprox2ToX(x) - 2^x | < (1.0 / 2^11) * (2^floor(x)). The following special cases apply to the EXP instruction: 1. RoughApprox2ToX(NaN) = NaN. 2. RoughApprox2ToX(-INF) = +0.0. 3. RoughApprox2ToX(+INF) = +INF. 4. RoughApprox2ToX(+/-0.0) = +1.0. The EXP instruction is present for compatibility with the original NV_vertex_program instruction set; it is recommended that applications using NV_vertex_program2 use the EX2 instruction instead. Section 2.14.3.15, FLR: Floor The FLR instruction performs a component-wise floor operation on the operand to generate a result vector. The floor of a value is defined as the largest integer less than or equal to the value. The floor of 2.3 is 2.0; the floor of -3.6 is -4.0. tmp = VectorLoad(op0); result.x = floor(tmp.x); result.y = floor(tmp.y); result.z = floor(tmp.z); result.w = floor(tmp.w); The following special-case rules apply to floor computation: 1. floor(NaN) = NaN. 2. floor(<x>) = <x>, for -0.0, +0.0, -INF, and +INF. In all cases, the sign of the result is equal to the sign of the operand. The FLR instruction is available only in the VP2 execution environment. Section 2.14.3.16, FRC: Fraction The FRC instruction extracts the fractional portion of each component of the operand to generate a result vector. The fractional portion of a component is defined as the result after subtracting off the floor of the component (see FLR), and is always in the range [0.00, 1.00). For negative values, the fractional portion is NOT the number written to the right of the decimal point -- the fractional portion of -1.7 is not 0.7 -- it is 0.3. 0.3 is produced by subtracting the floor of -1.7 (-2.0) from -1.7. tmp = VectorLoad(op0); result.x = tmp.x - floor(tmp.x); result.y = tmp.y - floor(tmp.y); result.z = tmp.z - floor(tmp.z); result.w = tmp.w - floor(tmp.w); The following special-case rules, which can be derived from the rules for FLR and ADD apply to fraction computation: 1. fraction(NaN) = NaN. 2. fraction(+/-INF) = NaN. 3. fraction(+/-0.0) = +0.0. The FRC instruction is available only in the VP2 execution environment. Section 2.14.3.17, LG2: Logarithm Base 2 The LG2 instruction approximates the base 2 logarithm of the scalar operand and replicates it to all four components of the result vector. tmp = ScalarLoad(op0); result.x = ApproxLog2(tmp); result.y = ApproxLog2(tmp); result.z = ApproxLog2(tmp); result.w = ApproxLog2(tmp); The approximation function is accurate to at least 22 bits: | ApproxLog2(x) - log_2(x) | < 1.0 / 2^22. Note that for large values of x, there are not enough bits in the floating-point storage format to represent a result that precisely. The following special-case rules apply to logarithm approximation: 1. ApproxLog2(NaN) = NaN. 2. ApproxLog2(+INF) = +INF. 3. ApproxLog2(+/-0.0) = -INF. 4. ApproxLog2(x) = NaN, -INF < x < -0.0. 5. ApproxLog2(-INF) = NaN. The LG2 instruction is available only in the VP2 execution environment. Section 2.14.3.18, LIT: Compute Light Coefficients The LIT instruction accelerates per-vertex lighting by computing lighting coefficients for ambient, diffuse, and specular light contributions. The "x" component of the operand is assumed to hold a diffuse dot product (n dot VP_pli, as in the vertex lighting equations in Section 2.13.1). The "y" component of the operand is assumed to hold a specular dot product (n dot h_i). The "w" component of the operand is assumed to hold the specular exponent of the material (s_rm), and is clamped to the range (-128, +128) exclusive. The "x" component of the result vector receives the value that should be multiplied by the ambient light/material product (always 1.0). The "y" component of the result vector receives the value that should be multiplied by the diffuse light/material product (n dot VP_pli). The "z" component of the result vector receives the value that should be multiplied by the specular light/material product (f_i * (n dot h_i) ^ s_rm). The "w" component of the result is the constant 1.0. Negative diffuse and specular dot products are clamped to 0.0, as is done in the standard per-vertex lighting operations. In addition, if the diffuse dot product is zero or negative, the specular coefficient is forced to zero. tmp = VectorLoad(op0); if (t.x < 0) t.x = 0; if (t.y < 0) t.y = 0; if (t.w < -(128.0-epsilon)) t.w = -(128.0-epsilon); else if (t.w > 128-epsilon) t.w = 128-epsilon; result.x = 1.0; result.y = t.x; result.z = (t.x > 0) ? RoughApproxPower(t.y, t.w) : 0.0; result.w = 1.0; The exponentiation approximation function is defined in terms of the base 2 exponentiation and logarithm approximation operations in the EXP and LOG instructions, including errors and the processing of any special cases. In particular, RoughApproxPower(a,b) = RoughApproxExp2(b * RoughApproxLog2(a)). The following special-case rules, which can be derived from the rules in the LOG, MUL, and EXP instructions, apply to exponentiation: 1. RoughApproxPower(NaN, <x>) = NaN, 2. RoughApproxPower(<x>, <y>) = NaN, if x <= -0.0, 3. RoughApproxPower(+/-0.0, <x>) = +0.0, if x > +0.0, or +INF, if x < -0.0, 4. RoughApproxPower(+1.0, <x>) = +1.0, if x is not NaN, 5. RoughApproxPower(+INF, <x>) = +INF, if x > +0.0, or +0.0, if x < -0.0, 6. RoughApproxPower(<x>, +/-0.0) = +1.0, if x >= -0.0 7. RoughApproxPower(<x>, +INF) = +0.0, if -0.0 <= x < +1.0, +INF, if x > +1.0, 8. RoughApproxPower(<x>, +INF) = +INF, if -0.0 <= x < +1.0, +0.0, if x > +1.0, 9. RoughApproxPower(<x>, +1.0) = <x>, if x >= +0.0, and 10. RoughApproxPower(<x>, NaN) = NaN. Section 2.14.3.19, LOG: Logarithm Base 2 (Approximate) The LOG instruction computes a rough approximation of the base 2 logarithm of the absolute value of the scalar operand. The approximation is returned in the "z" component of the result vector. A vertex program can also use the "x" and "y" components of the result vector to generate a more accurate approximation by evaluating result.x + f(result.y), where f(x) is a user-defined function that approximates 2^x over the domain [1.0, 2.0). The "w" component of the result vector is always 1.0. The exact behavior is specified in the following pseudo-code: tmp = fabs(ScalarLoad(op0)); result.x = floor(log2(tmp)); result.y = tmp / (2^floor(log2(tmp))); result.z = RoughApproxLog2(tmp); result.w = 1.0; The approximation function is accurate to at least 11 bits: | RoughApproxLog2(x) - log_2(x) | < 1.0 / 2^11. The following special-case rules apply to the LOG instruction: 1. RoughApproxLog2(NaN) = NaN. 2. RoughApproxLog2(+INF) = +INF. 3. RoughApproxLog2(+0.0) = -INF. The LOG instruction is present for compatibility with the original NV_vertex_program instruction set; it is recommended that applications using NV_vertex_program2 use the LG2 instruction instead. Section 2.14.3.20, MAD: Multiply And Add The MAD instruction performs a component-wise multiply of the first two operands, and then does a component-wise add of the product to the third operand to yield a result vector. tmp0 = VectorLoad(op0); tmp1 = VectorLoad(op1); tmp2 = VectorLoad(op2); result.x = tmp0.x * tmp1.x + tmp2.x; result.y = tmp0.y * tmp1.y + tmp2.y; result.z = tmp0.z * tmp1.z + tmp2.z; result.w = tmp0.w * tmp1.w + tmp2.w; All special case rules applicable to the ADD and MUL instructions apply to the individual components of the MAD operation as well. Section 2.14.3.21, MAX: Maximum The MAX instruction computes component-wise maximums of the values in the two operands to yield a result vector. tmp0 = VectorLoad(op0); tmp1 = VectorLoad(op1); result.x = max(tmp0.x, tmp1.x); result.y = max(tmp0.y, tmp1.y); result.z = max(tmp0.z, tmp1.z); result.w = max(tmp0.w, tmp1.w); The following special cases apply to the maximum operation: 1. max(A,B) is always equivalent to max(B,A). 2. max(NaN, <x>) == NaN, for all <x>. Section 2.14.3.22, MIN: Minimum The MIN instruction computes component-wise minimums of the values in the two operands to yield a result vector. tmp0 = VectorLoad(op0); tmp1 = VectorLoad(op1); result.x = min(tmp0.x, tmp1.x); result.y = min(tmp0.y, tmp1.y); result.z = min(tmp0.z, tmp1.z); result.w = min(tmp0.w, tmp1.w); The following special cases apply to the minimum operation: 1. min(A,B) is always equivalent to min(B,A). 2. min(NaN, <x>) == NaN, for all <x>. Section 2.14.3.23, MOV: Move The MOV instruction copies the value of the operand to yield a result vector. result = VectorLoad(op0); Section 2.14.3.24, MUL: Multiply The MUL instruction performs a component-wise multiply of the two operands to yield a result vector. tmp0 = VectorLoad(op0); tmp1 = VectorLoad(op1); result.x = tmp0.x * tmp1.x; result.y = tmp0.y * tmp1.y; result.z = tmp0.z * tmp1.z; result.w = tmp0.w * tmp1.w; The following special-case rules apply to multiplication: 1. "A*B" is always equivalent to "B*A". 2. NaN * <x> = NaN, for all <x>. 3. +/-0.0 * +/-INF = NaN. 4. +/-0.0 * <x> = +/-0.0, for all <x> except -INF, +INF, and NaN. The sign of the result is positive if the signs of the two operands match and negative otherwise. 5. +/-INF * <x> = +/-INF, for all <x> except -0.0, +0.0, and NaN. The sign of the result is positive if the signs of the two operands match and negative otherwise. 6. +1.0 * <x> = <x>, for all <x>. Section 2.14.3.25, RCC: Reciprocal (Clamped) The RCC instruction approximates the reciprocal of the scalar operand, clamps the result to one of two ranges, and replicates the clamped result to all four components of the result vector. If the approximate reciprocal is greater than 0.0, the result is clamped to the range [2^-64, 2^+64]. If the approximate reciprocal is not greater than zero, the result is clamped to the range [-2^+64, -2^-64]. tmp = ScalarLoad(op0); result.x = ClampApproxReciprocal(tmp); result.y = ClampApproxReciprocal(tmp); result.z = ClampApproxReciprocal(tmp); result.w = ClampApproxReciprocal(tmp); The approximation function is accurate to at least 22 bits: | ClampApproxReciprocal(x) - (1/x) | < 1.0 / 2^22, if 1.0 <= x < 2.0. The following special-case rules apply to reciprocation: 1. ClampApproxReciprocal(NaN) = NaN. 2. ClampApproxReciprocal(+INF) = +2^-64. 3. ClampApproxReciprocal(-INF) = -2^-64. 4. ClampApproxReciprocal(+0.0) = +2^64. 5. ClampApproxReciprocal(-0.0) = -2^64. 6. ClampApproxReciprocal(x) = +2^-64, if -2^64 < x < +INF. 7. ClampApproxReciprocal(x) = -2^-64, if -INF < x < -2^-64. 8. ClampApproxReciprocal(x) = +2^64, if +0.0 < x < +2^-64. 9. ClampApproxReciprocal(x) = -2^64, if -2^-64 < x < -0.0. The RCC instruction is available only in the VP1.1 and VP2 execution environments. Section 2.14.3.26, RCP: Reciprocal The RCP instruction approximates the reciprocal of the scalar operand and replicates it to all four components of the result vector. tmp = ScalarLoad(op0); result.x = ApproxReciprocal(tmp); result.y = ApproxReciprocal(tmp); result.z = ApproxReciprocal(tmp); result.w = ApproxReciprocal(tmp); The approximation function is accurate to at least 22 bits: | ApproxReciprocal(x) - (1/x) | < 1.0 / 2^22, if 1.0 <= x < 2.0. The following special-case rules apply to reciprocation: 1. ApproxReciprocal(NaN) = NaN. 2. ApproxReciprocal(+INF) = +0.0. 3. ApproxReciprocal(-INF) = -0.0. 4. ApproxReciprocal(+0.0) = +INF. 5. ApproxReciprocal(-0.0) = -INF. Section 2.14.3.27, RET: Subroutine Call Return The RET instruction conditionally returns from a subroutine initiated by a CAL instruction by popping an instruction reference off the top of the call stack and transferring control to the referenced instruction. The following pseudocode describes the operation of the instruction: if (TestCC(cc.c***) || TestCC(cc.*c**) || TestCC(cc.**c*) || TestCC(cc.***c)) { if (callStackDepth <= 0) { // terminate vertex program } else { callStackDepth--; instruction = callStack[callStackDepth]; } // continue execution at <instruction> } else { // do nothing } In the pseudocode, <callStackDepth> is the depth of the call stack, <callStack> is an array holding the call stack, and <instruction> is a reference to an instruction previously pushed onto the call stack. The RET instruction is available only in the VP2 execution environment. Section 2.14.3.28, RSQ: Reciprocal Square Root The RSQ instruction approximates the reciprocal of the square root of the scalar operand and replicates it to all four components of the result vector. tmp = ScalarLoad(op0); result.x = ApproxRSQRT(tmp); result.y = ApproxRSQRT(tmp); result.z = ApproxRSQRT(tmp); result.w = ApproxRSQRT(tmp); The approximation function is accurate to at least 22 bits: | ApproxRSQRT(x) - (1/x) | < 1.0 / 2^22, if 1.0 <= x < 4.0. The following special-case rules apply to reciprocal square roots: 1. ApproxRSQRT(NaN) = NaN. 2. ApproxRSQRT(+INF) = +0.0. 3. ApproxRSQRT(-INF) = NaN. 4. ApproxRSQRT(+0.0) = +INF. 5. ApproxRSQRT(-0.0) = -INF. 6. ApproxRSQRT(x) = NaN, if -INF < x < -0.0. Section 2.14.3.29, SEQ: Set on Equal The SEQ instruction performs a component-wise comparison of the two operands. Each component of the result vector is 1.0 if the corresponding component of the first operand is equal to that of the second, and 0.0 otherwise. tmp0 = VectorLoad(op0); tmp1 = VectorLoad(op1); result.x = (tmp0.x == tmp1.x) ? 1.0 : 0.0; result.y = (tmp0.y == tmp1.y) ? 1.0 : 0.0; result.z = (tmp0.z == tmp1.z) ? 1.0 : 0.0; result.w = (tmp0.w == tmp1.w) ? 1.0 : 0.0; if (tmp0.x is NaN or tmp1.x is NaN) result.x = NaN; if (tmp0.y is NaN or tmp1.y is NaN) result.y = NaN; if (tmp0.z is NaN or tmp1.z is NaN) result.z = NaN; if (tmp0.w is NaN or tmp1.w is NaN) result.w = NaN; The following special-case rules apply to SEQ: 1. (<x> == <y>) and (<y> == <x>) always produce the same result. 1. (NaN == <x>) is FALSE for all <x>, including NaN. 2. (+INF == +INF) and (-INF == -INF) are TRUE. 3. (-0.0 == +0.0) and (+0.0 == -0.0) are TRUE. The SEQ instruction is available only in the VP2 execution environment. Section 2.14.3.30, SFL: Set on False The SFL instruction is a degenerate case of the other "Set on" instructions that sets all components of the result vector to 0.0. result.x = 0.0; result.y = 0.0; result.z = 0.0; result.w = 0.0; The SFL instruction is available only in the VP2 execution environment. Section 2.14.3.31, SGE: Set on Greater Than or Equal The SGE instruction performs a component-wise comparison of the two operands. Each component of the result vector is 1.0 if the corresponding component of the first operands is greater than or equal that of the second, and 0.0 otherwise. tmp0 = VectorLoad(op0); tmp1 = VectorLoad(op1); result.x = (tmp0.x >= tmp1.x) ? 1.0 : 0.0; result.y = (tmp0.y >= tmp1.y) ? 1.0 : 0.0; result.z = (tmp0.z >= tmp1.z) ? 1.0 : 0.0; result.w = (tmp0.w >= tmp1.w) ? 1.0 : 0.0; if (tmp0.x is NaN or tmp1.x is NaN) result.x = NaN; if (tmp0.y is NaN or tmp1.y is NaN) result.y = NaN; if (tmp0.z is NaN or tmp1.z is NaN) result.z = NaN; if (tmp0.w is NaN or tmp1.w is NaN) result.w = NaN; The following special-case rules apply to SGE: 1. (NaN >= <x>) and (<x> >= NaN) are FALSE for all <x>. 2. (+INF >= +INF) and (-INF >= -INF) are TRUE. 3. (-0.0 >= +0.0) and (+0.0 >= -0.0) are TRUE. Section 2.14.3.32, SGT: Set on Greater Than The SGT instruction performs a component-wise comparison of the two operands. Each component of the result vector is 1.0 if the corresponding component of the first operands is greater than that of the second, and 0.0 otherwise. tmp0 = VectorLoad(op0); tmp1 = VectorLoad(op1); result.x = (tmp0.x > tmp1.x) ? 1.0 : 0.0; result.y = (tmp0.y > tmp1.y) ? 1.0 : 0.0; result.z = (tmp0.z > tmp1.z) ? 1.0 : 0.0; result.w = (tmp0.w > tmp1.w) ? 1.0 : 0.0; if (tmp0.x is NaN or tmp1.x is NaN) result.x = NaN; if (tmp0.y is NaN or tmp1.y is NaN) result.y = NaN; if (tmp0.z is NaN or tmp1.z is NaN) result.z = NaN; if (tmp0.w is NaN or tmp1.w is NaN) result.w = NaN; The following special-case rules apply to SGT: 1. (NaN > <x>) and (<x> > NaN) are FALSE for all <x>. 2. (-0.0 > +0.0) and (+0.0 > -0.0) are FALSE. The SGT instruction is available only in the VP2 execution environment. Section 2.14.3.33, SIN: Sine The SIN instruction approximates the sine of the angle specified by the scalar operand and replicates it to all four components of the result vector. The angle is specified in radians and does not have to be in the range [0,2*PI]. tmp = ScalarLoad(op0); result.x = ApproxSine(tmp); result.y = ApproxSine(tmp); result.z = ApproxSine(tmp); result.w = ApproxSine(tmp); The approximation function is accurate to at least 22 bits with an angle in the range [0,2*PI]. | ApproxSine(x) - sin(x) | < 1.0 / 2^22, if 0.0 <= x < 2.0 * PI. The error in the approximation will typically increase with the absolute value of the angle when the angle falls outside the range [0,2*PI]. The following special-case rules apply to cosine approximation: 1. ApproxSine(NaN) = NaN. 2. ApproxSine(+/-INF) = NaN. 3. ApproxSine(+/-0.0) = +/-0.0. The sign of the result is equal to the sign of the single operand. The SIN instruction is available only in the VP2 execution environment. Section 2.14.3.34, SLE: Set on Less Than or Equal The SLE instruction performs a component-wise comparison of the two operands. Each component of the result vector is 1.0 if the corresponding component of the first operand is less than or equal to that of the second, and 0.0 otherwise. tmp0 = VectorLoad(op0); tmp1 = VectorLoad(op1); result.x = (tmp0.x <= tmp1.x) ? 1.0 : 0.0; result.y = (tmp0.y <= tmp1.y) ? 1.0 : 0.0; result.z = (tmp0.z <= tmp1.z) ? 1.0 : 0.0; result.w = (tmp0.w <= tmp1.w) ? 1.0 : 0.0; if (tmp0.x is NaN or tmp1.x is NaN) result.x = NaN; if (tmp0.y is NaN or tmp1.y is NaN) result.y = NaN; if (tmp0.z is NaN or tmp1.z is NaN) result.z = NaN; if (tmp0.w is NaN or tmp1.w is NaN) result.w = NaN; The following special-case rules apply to SLE: 1. (NaN <= <x>) and (<x> <= NaN) are FALSE for all <x>. 2. (+INF <= +INF) and (-INF <= -INF) are TRUE. 3. (-0.0 <= +0.0) and (+0.0 <= -0.0) are TRUE. The SLE instruction is available only in the VP2 execution environment. Section 2.14.3.35, SLT: Set on Less Than The SLT instruction performs a component-wise comparison of the two operands. Each component of the result vector is 1.0 if the corresponding component of the first operand is less than that of the second, and 0.0 otherwise. tmp0 = VectorLoad(op0); tmp1 = VectorLoad(op1); result.x = (tmp0.x < tmp1.x) ? 1.0 : 0.0; result.y = (tmp0.y < tmp1.y) ? 1.0 : 0.0; result.z = (tmp0.z < tmp1.z) ? 1.0 : 0.0; result.w = (tmp0.w < tmp1.w) ? 1.0 : 0.0; if (tmp0.x is NaN or tmp1.x is NaN) result.x = NaN; if (tmp0.y is NaN or tmp1.y is NaN) result.y = NaN; if (tmp0.z is NaN or tmp1.z is NaN) result.z = NaN; if (tmp0.w is NaN or tmp1.w is NaN) result.w = NaN; The following special-case rules apply to SLT: 1. (NaN < <x>) and (<x> < NaN) are FALSE for all <x>. 2. (-0.0 < +0.0) and (+0.0 < -0.0) are FALSE. Section 2.14.3.36, SNE: Set on Not Equal The SNE instruction performs a component-wise comparison of the two operands. Each component of the result vector is 1.0 if the corresponding component of the first operand is not equal to that of the second, and 0.0 otherwise. tmp0 = VectorLoad(op0); tmp1 = VectorLoad(op1); result.x = (tmp0.x != tmp1.x) ? 1.0 : 0.0; result.y = (tmp0.y != tmp1.y) ? 1.0 : 0.0; result.z = (tmp0.z != tmp1.z) ? 1.0 : 0.0; result.w = (tmp0.w != tmp1.w) ? 1.0 : 0.0; if (tmp0.x is NaN or tmp1.x is NaN) result.x = NaN; if (tmp0.y is NaN or tmp1.y is NaN) result.y = NaN; if (tmp0.z is NaN or tmp1.z is NaN) result.z = NaN; if (tmp0.w is NaN or tmp1.w is NaN) result.w = NaN; The following special-case rules apply to SNE: 1. (<x> != <y>) and (<y> != <x>) always produce the same result. 2. (NaN != <x>) is TRUE for all <x>, including NaN. 3. (+INF != +INF) and (-INF != -INF) are FALSE. 4. (-0.0 != +0.0) and (+0.0 != -0.0) are TRUE. The SNE instruction is available only in the VP2 execution environment. Section 2.14.3.37, SSG: Set Sign The SSG instruction generates a result vector containing the signs of each component of the single operand. Each component of the result vector is 1.0 if the corresponding component of the operand is greater than zero, 0.0 if the corresponding component of the operand is equal to zero, and -1.0 if the corresponding component of the operand is less than zero. tmp = VectorLoad(op0); result.x = SetSign(tmp.x); result.y = SetSign(tmp.y); result.z = SetSign(tmp.z); result.w = SetSign(tmp.w); The following special-case rules apply to SSG: 1. SetSign(NaN) = NaN. 2. SetSign(-0.0) = SetSign(+0.0) = 0.0. 3. SetSign(-INF) = -1.0. 4. SetSign(+INF) = +1.0. 5. SetSign(x) = -1.0, if -INF < x < -0.0. 6. SetSign(x) = +1.0, if +0.0 < x < +INF. The SSG instruction is available only in the VP2 execution environment. Section 2.14.3.38, STR: Set on True The STR instruction is a degenerate case of the other "Set on" instructions that sets all components of the result vector to 1.0. result.x = 1.0; result.y = 1.0; result.z = 1.0; result.w = 1.0; The STR instruction is available only in the VP2 execution environment. Section 2.14.3.39, SUB: Subtract The SUB instruction performs a component-wise subtraction of the second operand from the first to yield a result vector. tmp0 = VectorLoad(op0); tmp1 = VectorLoad(op1); result.x = tmp0.x - tmp1.x; result.y = tmp0.y - tmp1.y; result.z = tmp0.z - tmp1.z; result.w = tmp0.w - tmp1.w; The SUB instruction is completely equivalent to an identical ADD instruction in which the negate operator on the second operand is reversed: 1. "SUB R0, R1, R2" is equivalent to "ADD R0, R1, -R2". 2. "SUB R0, R1, -R2" is equivalent to "ADD R0, R1, R2". 3. "SUB R0, R1, |R2|" is equivalent to "ADD R0, R1, -|R2|". 4. "SUB R0, R1, -|R2|" is equivalent to "ADD R0, R1, |R2|". The SUB instruction is available only in the VP1.1 and VP2 execution environments. 2.14.4 Vertex Arrays for Vertex Attributes Data for vertex attributes in vertex program mode may be specified using vertex array commands. The client may specify and enable any of sixteen vertex attribute arrays. The vertex attribute arrays are ignored when vertex program mode is disabled. When vertex program mode is enabled, vertex attribute arrays are used. The command void VertexAttribPointerNV(uint index, int size, enum type, sizei stride, const void *pointer); describes the locations and organizations of the sixteen vertex attribute arrays. index specifies the particular vertex attribute to be described. size indicates the number of values per vertex that are stored in the array; size must be one of 1, 2, 3, or 4. type specifies the data type of the values stored in the array. type must be one of SHORT, FLOAT, DOUBLE, or UNSIGNED_BYTE and these values correspond to the array types short, int, float, double, and ubyte respectively. The INVALID_OPERATION error is generated if type is UNSIGNED_BYTE and size is not 4. The INVALID_VALUE error is generated if index is greater than 15. The INVALID_VALUE error is generated if stride is negative. The one, two, three, or four values in an array that correspond to a single vertex attribute comprise an array element. The values within each array element at stored sequentially in memory. If the stride is specified as zero, then array elements are stored sequentially as well. Otherwise points to the ith and (i+1)st elements of an array differ by stride basic machine units (typically unsigned bytes), the pointer to the (i+1)st element being greater. pointer specifies the location in memory of the first value of the first element of the array being specified. Vertex attribute arrays are enabled with the EnableClientState command and disabled with the DisableClientState command. The value of the argument to either command is VERTEX_ATTRIB_ARRAYi_NV where i is an integer between 0 and 15; specifying a value of i enables or disables the vertex attribute array with index i. The constants obey VERTEX_ATTRIB_ARRAYi_NV = VERTEX_ATTRIB_ARRAY0_NV + i. When vertex program mode is enabled, the ArrayElement command operates as described in this section in contrast to the behavior described in section 2.8. Likewise, any vertex array transfer commands that are defined in terms of ArrayElement (DrawArrays, DrawElements, and DrawRangeElements) assume the operation of ArrayElement described in this section when vertex program mode is enabled. When vertex program mode is enabled, the ArrayElement command transfers the ith element of particular enabled vertex arrays as described below. For each enabled vertex attribute array, it is as though the corresponding command from section 2.14.1.1 were called with a pointer to element i. For each vertex attribute, the corresponding command is VertexAttrib[size][type]v, where size is one of [1,2,3,4], and type is one of [s,f,d,ub], corresponding to the array types short, int, float, double, and ubyte respectively. However, if a given vertex attribute array is disabled, but its corresponding aliased conventional per-vertex parameter's vertex array (as described in section 2.14.1.6) is enabled, then it is as though the corresponding command from section 2.7 or section 2.6.2 were called with a pointer to element i. In this case, the corresponding command is determined as described in section 2.8's description of ArrayElement. If the vertex attribute array 0 is enabled, it is as though VertexAttrib[size][type]v(0, ...) is executed last, after the executions of other corresponding commands. If the vertex attribute array 0 is disabled but the vertex array is enabled, it is as though Vertex[size][type]v is executed last, after the executions of other corresponding commands. 2.14.5 Vertex State Programs Vertex state programs share the same instruction set as and a similar execution model to vertex programs. While vertex programs are executed implicitly when a vertex transformation is provoked, vertex state programs are executed explicitly, independently of any vertices. Vertex state programs can write program parameter registers, but may not write vertex result registers. Vertex state programs have not been extended beyond the the VP1.0 execution environment, and are offered solely for compatibility with that execution environment. The purpose of a vertex state program is to update program parameter registers by means of an application-defined program. Typically, an application will load a set of program parameters and then execute a vertex state program that reads and updates the program parameter registers. For example, a vertex state program might normalize a set of unnormalized vectors previously loaded as program parameters. The expectation is that subsequently executed vertex programs would use the normalized program parameters. Vertex state programs are loaded with the same LoadProgramNV command (see section 2.14.1.8) used to load vertex programs except that the target must be VERTEX_STATE_PROGRAM_NV when loading a vertex state program. Vertex state programs must conform to a more limited grammar than the grammar for vertex programs. The vertex state program grammar for syntactically valid sequences is the same as the grammar defined in section 2.14.1.8 with the following modified rules: <program> ::= <vp1-program> <vp1-program> ::= "!!VSP1.0" <programBody> "END" <dstReg> ::= <absProgParamReg> | <temporaryReg> <vertexAttribReg> ::= "v" "[" "0" "]" A vertex state program fails to load if it does not write at least one program parameter register. A vertex state program fails to load if it contains more than 128 instructions. A vertex state program fails to load if any instruction sources more than one unique program parameter register. A vertex state program fails to load if any instruction sources more than one unique vertex attribute register (this is necessarily true because only vertex attribute 0 is available in vertex state programs). The error INVALID_OPERATION is generated if a vertex state program fails to load because it is not syntactically correct or for one of the other reasons listed above. A successfully loaded vertex state program is parsed into a sequence of instructions. Each instruction is identified by its tokenized name. The operation of these instructions when executed is defined in section 2.14.1.10. Executing vertex state programs is legal only outside a Begin/End pair. A vertex state program may not read any vertex attribute register other than register zero. A vertex state program may not write any vertex result register. The command ExecuteProgramNV(enum target, uint id, const float *params); executes the vertex state program named by id. The target must be VERTEX_STATE_PROGRAM_NV and the id must be the name of program loaded with a target type of VERTEX_STATE_PROGRAM_NV. params points to an array of four floating-point values that are loaded into vertex attribute register zero (the only vertex attribute readable from a vertex state program). The INVALID_OPERATION error is generated if the named program is nonexistent, is invalid, or the program is not a vertex state program. A vertex state program may not be valid for reasons explained in section 2.14.5. 2.14.6, Program Options In the VP1.1 and VP2.0 execution environment, vertex programs may specify one or more program options that modify the execution environment, according to the <option> grammar rule. The set of options available to the program is described below. Section 2.14.6.1, Position-Invariant Vertex Program Option If <vp11-option> or <vp2-option> matches "NV_position_invariant", the vertex program is presumed to be position-invariant. By default, vertex programs are not position-invariant. Even if programs emulate the conventional OpenGL transformation model, they may still not produce the exact same transform results, due to rounding errors or different operation orders. Such programs may not work well for multi-pass rendering algorithms where the second and subsequent passes use an EQUAL depth test. Position-invariant vertex programs do not compute a final vertex position; instead, the GL computes vertex coordinates as described in section 2.10. This computation should produce exactly the same results as the conventional OpenGL transformation model, assuming vertex weighting and vertex blending are disabled. A vertex program that specifies the position-invariant option will fail to load if it writes to the HPOS result register. Additionally, in the VP1.1 execution environment, position-invariant programs can not use relative addressing for program parameters. Any position-invariant VP1.1 program matches the grammar rule <relProgParamReg>, will fail to load. No such restriction exists for VP2.0 programs. For position-invariant programs, the limit on the number of instructions allowed in a program is reduced by four: position-invariant VP1.1 and VP2.0 programs may have no more than 124 or 252 instructions, respectively. 2.14.7 Tracking Matrices As a convenience to applications, standard GL matrix state can be tracked into program parameter vectors. This permits vertex programs to access matrices specified through GL matrix commands. In addition to GL's conventional matrices, several additional matrices are available for tracking. These matrices have names of the form MATRIXi_NV where i is between zero and n-1 where n is the value of the MAX_TRACK_MATRICES_NV implementation dependent constant. The MATRIXi_NV constants obey MATRIXi_NV = MATRIX0_NV + i. The value of MAX_TRACK_MATRICES_NV must be at least eight. The maximum stack depth for tracking matrices is defined by the MAX_TRACK_MATRIX_STACK_DEPTH_NV and must be at least 1. The command TrackMatrixNV(enum target, uint address, enum matrix, enum transform); tracks a given transformed version of a particular matrix into a contiguous sequence of four vertex program parameter registers beginning at address. target must be VERTEX_PROGRAM_NV (though tracked matrices apply to vertex state programs as well because both vertex state programs and vertex programs shared the same program parameter registers). matrix must be one of NONE, MODELVIEW, PROJECTION, TEXTURE, TEXTUREi_ARB (where i is between 0 and n-1 where n is the number of texture units supported), COLOR (if the ARB_imaging subset is supported), MODELVIEW_PROJECTION_NV, or MATRIXi_NV. transform must be one of IDENTITY_NV, INVERSE_NV, TRANSPOSE_NV, or INVERSE_TRANSPOSE_NV. The INVALID_VALUE error is generated if address is not a multiple of four. The MODELVIEW_PROJECTION_NV matrix represents the concatenation of the current modelview and projection matrices. If M is the current modelview matrix and P is the current projection matrix, then the MODELVIEW_PROJECTION_NV matrix is C and computed as C = P M Matrix tracking for the specified program parameter register and the next consecutive three registers is disabled when NONE is supplied for matrix. When tracking is disabled the previously tracked program parameter registers retain the state of their last tracked values. Otherwise, the specified transformed version of matrix is tracked into the specified program parameter register and the next three registers. Whenever the matrix changes, the transformed version of the matrix is updated in the specified range of program parameter registers. If TEXTURE is specified for matrix, the texture matrix for the current active texture unit is tracked. If TEXTUREi_ARB is specified for matrix, the <i>th texture matrix is tracked. Matrices are tracked row-wise meaning that the top row of the transformed matrix is loaded into the program parameter address, the second from the top row of the transformed matrix is loaded into the program parameter address+1, the third from the top row of the transformed matrix is loaded into the program parameter address+2, and the bottom row of the transformed matrix is loaded into the program parameter address+3. The transformed matrix may be identical to the specified matrix, the inverse of the specified matrix, the transpose of the specified matrix, or the inverse transpose of the specified matrix, depending on the value of transform. When matrix tracking is enabled for a particular program parameter register sequence, updates to the program parameter using ProgramParameterNV commands, a vertex program, or a vertex state program are not possible. The INVALID_OPERATION error is generated if a ProgramParameterNV command is used to update a program parameter register currently tracking a matrix. The INVALID_OPERATION error is generated by ExecuteProgramNV when the vertex state program requested for execution writes to a program parameter register that is currently tracking a matrix because the program is considered invalid. 2.14.8 Required Vertex Program State The state required for vertex programs consists of: a bit indicating whether or not program mode is enabled; a bit indicating whether or not two-sided color mode is enabled; a bit indicating whether or not program-specified point size mode is enabled; 256 4-component floating-point program parameter registers; 16 4-component vertex attribute registers (though this state is aliased with the current normal, primary color, secondary color, fog coordinate, weights, and texture coordinate sets); 24 sets of matrix tracking state for each set of four sequential program parameter registers, consisting of a n-valued integer indicated the tracked matrix or GL_NONE (where n is 5 + the number of texture units supported + the number of tracking matrices supported) and a four-valued integer indicating the transformation of the tracked matrix; an unsigned integer naming the currently bound vertex program and the state must be maintained to indicate which integers are currently in use as program names. Each existent program object consists of a target, a boolean indicating whether the program is resident, an array of type ubyte containing the program string, and the length of the program string array. Initially, no program objects exist. Program mode, two-sided color mode, and program-specified point size mode are all initially disabled. The initial state of all 256 program parameter registers is (0,0,0,0). The initial state of the 16 vertex attribute registers is (0,0,0,1) except in cases where a vertex attribute register aliases to a conventional GL transform mode vertex parameter in which case the initial state is the initial state of the respective aliased conventional vertex parameter. The initial state of the 24 sets of matrix tracking state is NONE for the tracked matrix and IDENTITY_NV for the transformation of the tracked matrix. The initial currently bound program is zero. The client state required to implement the 16 vertex attribute arrays consists of 16 boolean values, 16 memory pointers, 16 integer stride values, 16 symbolic constants representing array types, and 16 integers representing values per element. Initially, the boolean values are each disabled, the memory pointers are each null, the strides are each zero, the array types are each FLOAT, and the integers representing values per element are each four."

Additions to Chapter 3 of the OpenGL 1.3 Specification (Rasterization) |

None.

Additions to Chapter 4 of the OpenGL 1.3 Specification (Per-Fragment Operations and the Frame Buffer) |

None.

Additions to Chapter 5 of the OpenGL 1.3 Specification (Special Functions) |

None.

Additions to Chapter 6 of the OpenGL 1.3 Specification (State and State Requests) |

None.

Additions to Appendix A of the OpenGL 1.3 Specification (Invariance) |

None.

Additions to the AGL/GLX/WGL Specifications |

None.

GLX Protocol |

All relevant protocol is defined in the NV_vertex_program extension.

Errors |

This list includes the errors specified in the NV_vertex_program extension, modified as appropriate. The error INVALID_VALUE is generated if VertexAttribNV is called where index is greater than 15. The error INVALID_VALUE is generated if any ProgramParameterNV has an index is greater than 255 (was 95 in NV_vertex_program). The error INVALID_VALUE is generated if VertexAttribPointerNV is called where index is greater than 15. The error INVALID_VALUE is generated if VertexAttribPointerNV is called where size is not one of 1, 2, 3, or 4. The error INVALID_VALUE is generated if VertexAttribPointerNV is called where stride is negative. The error INVALID_OPERATION is generated if VertexAttribPointerNV is called where type is UNSIGNED_BYTE and size is not 4. The error INVALID_VALUE is generated if LoadProgramNV is used to load a program with an id of zero. The error INVALID_OPERATION is generated if LoadProgramNV is used to load an id that is currently loaded with a program of a different program target. The error INVALID_OPERATION is generated if the program passed to LoadProgramNV fails to load because it is not syntactically correct based on the specified target. The value of PROGRAM_ERROR_POSITION_NV is still updated when this error is generated. The error INVALID_OPERATION is generated if LoadProgramNV has a target of VERTEX_PROGRAM_NV and the specified program fails to load because it does not write the HPOS register at least once. The value of PROGRAM_ERROR_POSITION_NV is still updated when this error is generated. The error INVALID_OPERATION is generated if LoadProgramNV has a target of VERTEX_STATE_PROGRAM_NV and the specified program fails to load because it does not write at least one program parameter register. The value of PROGRAM_ERROR_POSITION_NV is still updated when this error is generated. The error INVALID_OPERATION is generated if the vertex program or vertex state program passed to LoadProgramNV fails to load because it contains more than 128 instructions (VP1 programs) or 256 instructions (VP2 programs). The value of PROGRAM_ERROR_POSITION_NV is still updated when this error is generated. The error INVALID_OPERATION is generated if a program is loaded with LoadProgramNV for id when id is currently loaded with a program of a different target. The error INVALID_OPERATION is generated if BindProgramNV attempts to bind to a program name that is not a vertex program (for example, if the program is a vertex state program). The error INVALID_VALUE is generated if GenProgramsNV is called where n is negative. The error INVALID_VALUE is generated if AreProgramsResidentNV is called and any of the queried programs are zero or do not exist. The error INVALID_OPERATION is generated if ExecuteProgramNV executes a program that does not exist. The error INVALID_OPERATION is generated if ExecuteProgramNV executes a program that is not a vertex state program. The error INVALID_OPERATION is generated if Begin, RasterPos, or a command that performs an explicit Begin is called when vertex program mode is enabled and the currently bound vertex program writes program parameters that are currently being tracked. The error INVALID_OPERATION is generated if ExecuteProgramNV is called and the vertex state program to execute writes program parameters that are currently being tracked. The error INVALID_VALUE is generated if TrackMatrixNV has a target of VERTEX_PROGRAM_NV and attempts to track an address is not a multiple of four. The error INVALID_VALUE is generated if GetProgramParameterNV is called to query an index greater than 255 (was 95 in NV_vertex_program). The error INVALID_VALUE is generated if GetVertexAttribNV is called to query an <index> greater than 15, or if <index> is zero and <pname> is CURRENT_ATTRIB_NV. The error INVALID_VALUE is generated if GetVertexAttribPointervNV is called to query an index greater than 15. The error INVALID_OPERATION is generated if GetProgramivNV is called and the program named id does not exist. The error INVALID_OPERATION is generated if GetProgramStringNV is called and the program named <program> does not exist. The error INVALID_VALUE is generated if GetTrackMatrixivNV is called with an <address> that is not divisible by four or greater than or equal to 256 (was 96 in NV_vertex_program). The error INVALID_VALUE is generated if AreProgramsResidentNV, DeleteProgramsNV, GenProgramsNV, or RequestResidentProgramsNV are called where <n> is negative. The error INVALID_VALUE is generated if LoadProgramNV is called where <len> is negative. The error INVALID_VALUE is generated if ProgramParameters4dvNV or ProgramParameters4fvNV are called where <count> is negative. The error INVALID_VALUE is generated if VertexAttribs{1,2,3,4}{d,f,s}vNV is called where <count> is negative. The error INVALID_ENUM is generated if BindProgramNV, GetProgramParameterfvNV, GetProgramParameterdvNV, GetTrackMatrixivNV, ProgramParameter4fNV, ProgramParameter4dNV, ProgramParameter4fvNV, ProgramParameter4dvNV, ProgramParameters4fvNV, ProgramParameters4dvNV, or TrackMatrixNV are called where <target> is not VERTEX_PROGRAM_NV. The error INVALID_ENUM is generated if LoadProgramNV or ExecuteProgramNV are called where <target> is not either VERTEX_PROGRAM_NV or VERTEX_STATE_PROGRAM_NV.

New State |

(Modify Table X.5, New State Introduced by NV_vertex_program from the NV_vertex_program specification.) Get Value Type Get Command Initial Value Description Sec Attribute --------------------- ------ ----------------------- ------------- ------------------ -------- ------------ PROGRAM_PARAMETER_NV 256xR4 GetProgramParameterNV (0,0,0,0) program parameters 2.14.1.2 - (Modify Table X.7. Vertex Program Per-vertex Execution State. "VP1" and "VP2" refer to the VP1 and VP2 execution environments, respectively.) Get Value Type Get Command Initial Value Description Sec Attribute --------- ------ ----------- ------------- ----------------------- -------- --------- - 12xR4 - (0,0,0,0) VP1 temporary registers 2.14.1.4 - - 16xR4 - (0,0,0,0) VP2 temporary registers 2.14.1.4 - - 15xR4 - (0,0,0,1) vertex result registers 2.14.1.4 - Z4 - (0,0,0,0) VP1 address register 2.14.1.3 - 2xZ4 - (0,0,0,0) VP2 address registers 2.14.1.3 -

Revision History |

Rev. Date Author Changes ---- -------- ------- -------------------------------------------- 32 05/16/04 pbrown Documented that it's not possible to results from LG2 that are any more precise than what is available in the fp32 storage format. 31 08/17/03 pbrown Added several overlooked opcodes (RCC, SUB, SIN) to the grammar. They are documented in the spec body, however. 30 02/28/03 pbrown Fixed incorrect condition code example. 29 12/08/02 pbrown Fixed minor bug where "ABS" and "DPH" were listed twice in the grammar. 28 10/29/02 pbrown Remove support for indirect branching. Added missing o[CLPx] outputs to the grammar. Minor typo fixes. 25 07/19/02 pbrown Fixed several miscellaneous errors in the spec. 24 06/28/02 pbrown Fixed several erroneous resource limitations. 23 06/07/02 pbrown Removed stray and erroneous abs() from the documentation of the LG2 instruction. 22 06/06/02 pbrown Added missing items from NV_vertex_program1_1, in particular, program options. Documented the VP2.0 position-invariant programs have no restrictions on indirect addressing. 21 06/19/02 pbrown Cleaned up miscellaneous errors and issues in the spec. 20 05/17/02 pbrown Documented LOG instruction as taking the absolute value of the operand, as in VP1.0. Fixed special-case rules for MUL. Added clamps to special-case clamping rules for RCC. 18 05/09/02 pbrown Clarified the handling of NaN/UN in certain instructions and conditional operations. 17 04/26/02 pbrown Fix incorrectly specified algorithm for computing the y result in the LOG instruction. 16 04/21/02 pbrown Added example for "paletted skinning". Documented size limitation (10 bits) on the address register and ARA, ARL, and ARR instructions. The limits needs to be exposed because of the ARA instruction. Cleaned up documentation on absolute value on input operations. Added examples for masked writes and CC updates, and for branching. Fixed out-of-range indexed branch language and pseudocode to clamp to the actual table size (rather than the theoretical maximum). Documented ABS as semi-deprecated in VP2. Fixed special cases for MIN, MAX, SEQ, SGE, SGT, SLE, SLT, and SNE. Fix completely botched description of RET. 15 04/05/02 pbrown Updated introduction to indicate that ARL/ARR/ARA all can update condition code. Minor fixes and optimizations to the looping examples. Add missing "set on" opcodes to the grammar. Fixed spec to clamp branch table indices to [0,15]. Added a couple caveats to the "ABS" pseudo-instruction. Documented "ARR" as using IEEE round to nearest even mode. Documented special cases for "SSG". mode. Documented special cases for "SSG".

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