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GL_EXT_blend_color
homeprevnext Name
  
    EXT_blend_color  
  
homeprevnext Name Strings
  
    GL_EXT_blend_color  
  
homeprevnext Version
  
    $Date: 1995/03/31 04:40:19 $ $Revision: 1.7 $  
  
homeprevnext Number
  
    2  
  
homeprevnext Dependencies
  
    None  
  
homeprevnext Overview
  
    Blending capability is extended by defining a constant color that can  
    be included in blending equations.  A typical usage is blending two  
    RGB images.  Without the constant blend factor, one image must have  
    an alpha channel with each pixel set to the desired blend factor.  
  
homeprevnext New Procedures and Functions
  
    void BlendColorEXT(clampf red,  
                       clampf green,  
                       clampf blue,  
                       clampf alpha);  
  
homeprevnext New Tokens
  
    Accepted by the <sfactor> and <dfactor> parameters of BlendFunc:  
  
        CONSTANT_COLOR_EXT               0x8001  
        ONE_MINUS_CONSTANT_COLOR_EXT     0x8002  
        CONSTANT_ALPHA_EXT               0x8003  
        ONE_MINUS_CONSTANT_ALPHA_EXT     0x8004  
  
    Accepted by the <pname> parameter of GetBooleanv, GetIntegerv,  
    GetFloatv, and GetDoublev:  
  
        BLEND_COLOR_EXT                  0x8005  
  
homeprevnext Additions to Chapter 2 of the GL Specification (OpenGL Operation)
  
    None  
  
homeprevnext Additions to Chapter 3 of the GL Specification (Rasterization)
  
    None  
  
homeprevnext Additions to Chapter 4 of the GL Specification (Per-Fragment Operations and the Framebuffer)
  
    The commands that control blending are now BlendFunc and BlendColorEXT.  
    A constant color to be used in the blending equation is specified by  
    BlendColorEXT.  The four parameters are clamped to the range [0,1]  
    before being stored.  The default value for the constant blending color  
    is (0,0,0,0).  
  
    The constant color can be used in both the source and destination  
    blending factors.  Four lines are added to table 4.1 and table 4.2:  
  
        Value                           Blend Factors  
        -----                           -------------  
        ZERO                            (0, 0, 0, 0)  
        ONE                             (1, 1, 1, 1)  
        DST_COLOR                       (Rd/Kr, Gd/Kg, Bd/Kb, Ad/Ka)  
        ONE_MINUS_DST_COLOR             (1, 1, 1, 1) - (Rd/Kr,Gd/Kg,Bd/Kb,Ad/Ka)  
        SRC_ALPHA                       (As, As, As, As) / Ka  
        ONE_MINUS_SRC_ALPHA             (1, 1, 1, 1) - (As, As, As, As) / Ka  
        DST_ALPHA                       (Ad, Ad, Ad, Ad) / Ka  
        ONE_MINUS_DST_ALPHA             (1, 1, 1, 1) - (Ad, Ad, Ad, Ad) / Ka  
        CONSTANT_COLOR_EXT              (Rc, Gc, Bc, Ac)                                        NEW  
        ONE_MINUS_CONSTANT_COLOR_EXT    (1, 1, 1, 1) - (Rc, Gc, Bc, Ac)                         NEW  
        CONSTANT_ALPHA_EXT              (Ac, Ac, Ac, Ac)                                        NEW  
        ONE_MINUS_CONSTANT_ALPHA_EXT    (1, 1, 1, 1) - (Ac, Ac, Ac, Ac)                         NEW  
        SRC_ALPHA_SATURATE              (f, f, f, 1)  
  
        Table 4.1: Values controlling the source blending function and the  
        source blending values they compute.  Ka = 2**m - 1, where m is the  
        number of bits in the A color component.  Kr, Kg, and Kb are similarly  
        determined by the number of bits in the R, G, and B color components.  
        f = min(As, 1-Ad) / Ka.  
  
        Value                           Blend Factors  
        -----                           -------------  
        ZERO                            (0, 0, 0, 0)  
        ONE                             (1, 1, 1, 1)  
        SRC_COLOR                       (Rs/Kr, Gs/Kg, Bs/Kb, As/Ka)  
        ONE_MINUS_SRC_COLOR             (1, 1, 1, 1) - (Rs/Kr,Gs/Kg,Bs/Kb,As/Ka)  
        SRC_ALPHA                       (As, As, As, As) / Ka  
        ONE_MINUS_SRC_ALPHA             (1, 1, 1, 1) - (As, As, As, As) / Ka  
        DST_ALPHA                       (Ad, Ad, Ad, Ad) / Ka  
        ONE_MINUS_DST_ALPHA             (1, 1, 1, 1) - (Ad, Ad, Ad, Ad) / Ka  
        CONSTANT_COLOR_EXT              (Rc, Gc, Bc, Ac)                                        NEW  
        ONE_MINUS_CONSTANT_COLOR_EXT    (1, 1, 1, 1) - (Rc, Gc, Bc, Ac)                         NEW  
        CONSTANT_ALPHA_EXT              (Ac, Ac, Ac, Ac)                                        NEW  
        ONE_MINUS_CONSTANT_ALPHA_EXT    (1, 1, 1, 1) - (Ac, Ac, Ac, Ac)                         NEW  
  
        Table 4.2: Values controlling the destination blending function and  
        the destination blending values they compute.  Ka = 2**m - 1, where  
        m is the number of bits in the A color component.  Kr, Kg, and Kb  
        are similarly determined by the number of bits in the R, G, and B  
        color components.  
  
    Rc, Gc, Bc, and Ac are the four components of the constant blending  
    color.  These blend factors are not scaled by Kr, Kg, Kb, and Ka,  
    because they are already in the range [0,1].  
  
homeprevnext Additions to Chapter 5 of the GL Specification (Special Functions)
  
    None  
  
homeprevnext Additions to Chapter 6 of the GL Specification (State and State Requests)
  
    None  
  
homeprevnext Additions to the GLX Specification
  
    None  
  
homeprevnext GLX Protocol
  
    A new GL rendering command is added. The following command is sent to the   
    server as part of a glXRender request:  
  
        BlendColorEXT  
            2           20              rendering command length  
            2           4096            rendering command opcode  
            4           FLOAT32         red  
            4           FLOAT32         green  
            4           FLOAT32         blue  
            4           FLOAT32         alpha  
  
homeprevnext Errors
  
    INVALID_OPERATION is generated if BlendColorEXT is called between  
    execution of Begin and the corresponding call to End.  
  
homeprevnext New State
  
                                                Initial  
    Get Value           Get Command     Type    Value           Attrib  
    ---------           -----------     ----    -------         ------  
    BLEND_COLOR_EXT     GetFloatv       C       (0,0,0,0)       color-buffer  
  
homeprevnext New Implementation Dependent State
  
    None  
    None  
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