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  $Date: 1997/10/05 00:16:23 $ $Revision: 1.3 $  
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homeprevnext Dependencies
homeprevnext Overview
  This extension adds a second color to rasterization when lighting is   
  enabled.  Its purpose is to produce textured objects with specular   
  highlights which are the color of the lights.  It applies only to   
  rgba lighting.  
  The two colors are computed at the vertexes.  They are both clamped,   
  flat-shaded, clipped, and converted to fixed-point just like the   
  current rgba color (see Figure 2.8).  Rasterization interpolates   
  both colors to fragments.  If texture is enabled, the first (or   
  primary) color is the input to the texture environment; the fragment   
  color is the sum of the second color and the color resulting from   
  texture application.  If texture is not enabled, the fragment color   
  is the sum of the two colors.  
  A new control to LightModel*, LIGHT_MODEL_COLOR_CONTROL_EXT, manages   
  the values of the two colors.  It takes values: SINGLE_COLOR_EXT, a   
  compatibility mode, and SEPARATE_SPECULAR_COLOR_EXT, the object of   
  this extension.  In single color mode, the primary color is the   
  current final color and the secondary color is 0.0.  In separate   
  specular mode, the primary color is the sum of the ambient, diffuse,   
  and emissive terms of final color and the secondary color is the   
  specular term.  
  There is much concern that this extension may not be compatible with  
  the future direction of OpenGL with regards to better lighting and  
  shading models.  Until those impacts are resolved, serious  
  consideration should be given before adding to the interface  
  specified herein (for example, allowing the user to specify a  
  second input color).  
homeprevnext Issues
  * Where is emissive included?   
    RESOLVED - Emissive is included with the ambient and diffuse   
    terms.  Grouping emissive with specular (the "proper" thing) could   
    be implemented with a new value for the color control.  
* Should there be two colors when not lighting or with index   
    RESOLVED - The answer is probably yes--there should be two colors   
    when lighting is disabled and there could be an incorporation of   
    two colors with index lighting; but these are beyond the scope of   
    this extension.  Further, attempts to accomplish these may not be  
    compatible with the future direction of OpenGL with respect to  
    high quality lighting and shading models.  
  * What happens when texture is disabled?  
    RESOLVED - The extension specifies to add the two colors when   
    texture is disabled.  This is compatible with the philosophy of   
    "if texture is disabled, this mode does not apply".  
homeprevnext New Procedures and Functions
homeprevnext New Tokens
  Accepted by the <pname> parameter of LightModel*, and also by the   
  <pname> parameter of GetBooleanv, GetIntegerv, GetFloatv, and   
  Accepted by the <param> parameter of LightModel* when <pname> is   
    SINGLE_COLOR_EXT                    0x81F9  
homeprevnext Additions to Chapter 2 of the 1.0 Specification (OpenGL Operation)
  - (2.13, p. 40) Rework the second paragraph to acknowledge two  
    "Next, lighting, if enabled, produces either a color index or   
    primary and secondary colors.  If lighting is disabled, the   
    current color index or color is used in further processing (the   
    current color is the primary color and the secondary color is 0).    
    After lighting, colors are clamped..."  
  - (Figure 2.8, p. 41) Change RGBA to primary RGBA and secondary RGB:  
    Ideally, there might be an RGB2 underneath RGBA (both places).    
    Alternatively, a note in the caption could clarify that RGBA   
    referred to the primary RGBA and a secondary RGB.  (Speaking of   
    the caption, the part about "m is the number of bits an R, G, B,   
    or A component" could be removed as m doesn't appear in the   
  - (2.13.1, p. 42) Rework the opening of this section to not imply a   
    single color:  
    In the first sentence, change "a color" to "colors".  Rephrase the   
    itemization of the two lighting states to:  
    "1. Lighting Off. In this state, the current color is assigned to   
        the vertex primary color.  The vertex secondary color is 0.  
     2. Lighting On.  In this state, the vertex primary and secondary   
        colors are computed from the current lighting parameters."  
  - (Table 2.7, p.44) Add new entry (at the bottom):  
    Parameter  Type  Default Value     Description  
    ---------  ----  ----------------  ------------------------------  
    c_es       enum  SINGLE_COLOR_EXT  controls computation of colors  
  - (p. 45, top of page) Rephrase the first line and equation:  
    "Lighting produces two colors at a vertex: a primary color c_1 and   
    a secondary color c_2.  The values of c_1 and c_2 depend on the   
    light model color control, c_es (note: c_es should be in italics   
    and c_1 and c_2 in bold, so this really won't be as confusing as   
    it seems).  If c_es = SINGLE_COLOR_EXT, then the equations to   
    compute c_1 and c_2 are (note: the equation for c_1 is the current   
    equation for c):  
      c_1 = e_cm  
          + a_cm * a_cs  
          + SUM(att_i * spot_i * (a_cm * a_cli  
                               + dot(n, VP_pli) * d_cm * d_cli  
                               + f_i * dot(n, h_i)^s_rm * s_cm * s_cli)  
      c_2 = 0  
    If c_es = SEPARATE_SPECULAR_COLOR_EXT, then:  
      c_1 = e_cm  
          + a_cm * a_cs  
          + SUM (att_i * spot_i * (a_cm * a_cli  
                                + (n dot VP_pli) * d_cm * d_cli)  
      c_2 = SUM(att_i * spot_i * (f_i * (n dot h_i)^s_rm * s_cm * s_cli)  
  - (p. 45, second paragraph from bottom) Clarify that A is in the   
    primary color:  
    After the sentence "The value of A produced by lighting is the   
    alpha value associated with d_cm", add "A is always associated   
    with the primary color c_1; c_2 has no alpha component."  
  - (Table 2.8, p. 48) Add a new entry (at the bottom):  
    Parameter  Name                           Number of values  
    ---------  -----------------------------  ----------------   
    c_es       LIGHT_MODEL_COLOR_CONTROL_EXT         1  
  - (2.13.6, p. 51) Clarify that both primary and secondary colors are   
    Replace "RGBA" in the first line of the section with "both primary   
    and secondary".  
  - (2.13.7, p. 52) Clarify what happens to primary and secondary   
    colors when flat shading--reword the first paragraph:  
    "A primitive may be flatshaded, meaning that all vertices of the   
    primitive are assigned the same color index or primary and   
    secondary colors.  These come from the vertex that spawned the   
    primitive.  For a point, these are the colors associated with the   
    point.  For a line segment, they are the colors of the second   
    (final) vertex of the segment.  For a polygon, they come from a   
    selected vertex depending on how the polygon was generated.  Table   
    2.9 summarizes the possibilities."  
  - (2.13.8, p. 52) Rework to not imply a single color:  
    In the second sentence, change "If the color is" to "Those" and ",   
    it is" to "are".  In the first sentence of the next paragraph,   
    change "the color" to "two colors".  
homeprevnext Additions to Chapter 3 of the 1.0 Specification (Rasterization)
  - (Figure 3.1, p. 55) Add a box between texturing and fog called   
    "color sum".  
  - (3.8, p. 85) In the first paragraph, second sentence, insert   
    "primary" before RGBA.  Insert after this sentence "Texturing does   
    not affect the secondary color."  
  - (new section before 3.9) Insert new section titled "Color Sum":  
    "At the beginning of this stage in RGBA mode, a fragment has two   
    colors: a primary RGBA color (which texture, if enabled, may have   
    modified) and a secondary RGB color.  This stage sums the R, G,   
    and B components of these two colors to produce a single RGBA   
    color.  If the resulting RGB values exceed 1.0, they are clamped   
    to 1.0.  
    In color index mode, a fragment only has a single color index and   
    this stage does nothing."  
homeprevnext Additions to Chapter 4 of the 1.0 Specification (Per-Fragment Operations and the Frame Buffer)
homeprevnext Additions to Chapter 5 of the 1.0 Specification (Special Functions)
  - (5.3, p. 137) Specify that feedback returns the primary color by  
    changing the last sentence of the large paragraph in the middle  
    of the page to:  
    "The colors returned are the primary colors.  These colors and the  
    texture coordinates are those resulting from the clipping operations  
    as described in section 2.13.8."  
homeprevnext Additions to Chapter 6 of the 1.0 Specification (State and State Requests)
  - (Table 6.9, p. 157) Add:  
    Type - Z2  
    Get Cmnd - GetIntegerv  
    Initial Value - SINGLE_COLOR_EXT  
    Description - color control  
    Sec. - (whatever it ends up as)  
    Attribute - lighting  
homeprevnext Additions to the GLX Specification
homeprevnext GLX Protocol
homeprevnext Errors
homeprevnext New State
  (see changes to table 6.9)  
  (see changes to table 6.9)  
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