EXT_draw_instanced
GL_EXT_draw_instanced
Michael Gold, NVIDIA Corporation (gold 'at' nvidia.com)
Shipping for GeForce 8 Series (November 2006)
Last Modified Date: November 6, 2006
Author Revision: 1.4
Unassigned
OpenGL 2.0 is required.
EXT_gpu_shader4 or NV_vertex_shader4 is required.
This extension provides the means to render multiple instances of
an object with a single draw call, and an "instance ID" variable
which can be used by the vertex program to compute per-instance
values, typically an object's transform.
   New Procedures and Functions |
void DrawArraysInstancedEXT(enum mode, int first, sizei count,
sizei primcount);
void DrawElementsInstancedEXT(enum mode, sizei count, enum type,
const void *indices, sizei primcount);
| Additions to Chapter 2 of the OpenGL 2.0 Specification (OpenGL Operation) |
Modify section 2.8 (Vertex Arrays), p. 23
(insert before the final paragraph, p. 30)
The internal counter <instanceID> is a 32-bit integer value which
may be read by a vertex program as <vertex.instance>, as described
in section 2.X.3.2, or vertex shader as <gl_InstanceID>, as
described in section 2.15.4.2. The value of this counter is
always zero, except as noted below.
The command
void DrawArraysInstancedEXT(enum mode, int first, sizei count,
sizei primcount);
behaves identically to DrawArrays except that <primcount>
instances of the range of elements are executed and the value of
<instanceID> advances for each iteration. It has the same effect
as:
if (mode or count is invalid)
generate appropriate error
else {
for (i = 0; i < primcount; i++) {
instanceID = i;
DrawArrays(mode, first, count, i);
}
instanceID = 0;
}
The command
void DrawElementsInstancedEXT(enum mode, sizei count, enum type,
const void *indices, sizei primcount);
behaves identically to DrawElements except that <primcount>
instances of the set of elements are executed, and the value of
<instanceID> advances for each iteration. It has the same effect
as:
if (mode, count, or type is invalid )
generate appropriate error
else {
for (int i = 0; i < primcount; i++) {
instanceID = i;
DrawElements(mode, count, type, indices, i);
}
instanceID = 0;
}
| Additions to Chapter 5 of the OpenGL 2.0 Specification (Special Functions) |
The error INVALID_OPERATION is generated if DrawArraysInstancedEXT
or DrawElementsInstancedEXT is called during display list
compilation.
| Dependencies on NV_vertex_program4 |
If NV_vertex_program4 is not supported, all references to
vertex.instance are deleted.
| Dependencies on EXT_gpu_shader4 |
If EXT_gpu_shader4 is not supported, all references to
gl_InstanceID are deleted.
INVALID_ENUM is generated by DrawElementsInstancedEXT if <type> is
not one of UNSIGNED_BYTE, UNSIGNED_SHORT or UNSIGNED_INT.
INVALID_VALUE is generated by DrawArraysInstancedEXT if <first> is
less than zero.
(1) Should instanceID be provided by this extension, or should it be
provided by EXT_gpu_shader4, thus creating a dependence on that
spec?
Resolved: While this extension could stand alone, its utility
would be limited without the additional functionality provided
by EXT_gpu_shader4; also, the spec language is cleaner if
EXT_gpu_shader4 assumes instanceID is always available, even
if its value is always zero without this extension.
(2) Should MultiDrawArrays and MultiDrawElements affect the value of
instanceID?
Resolved: No, this may cause implementation difficulties and
is considered unlikely to provide any real benefit.
(3) Should DrawArraysInstanced and DrawElementsInstanced be compiled
into display lists?
Resolved: No, calling these during display list compilation
generate INVALID_OPERATION.
None
None
 |  | Last update: November 14, 2006.
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