OES_blend_func_separate

GL_OES_blend_func_separate

Benj Lipchak, Apple (lipchak 'at' apple.com)

Copyright (c) 2009-2013 The Khronos Group Inc. Copyright terms at
    http://www.khronos.org/registry/speccopyright.html

Khronos-approved extension specifications are updated in response to
issues and bugs prioritized by the Khronos OpenGL ES Working Group. For
extensions which have been promoted to a core Specification, fixes will
first appear in the latest version of that core Specification, and will
eventually be backported to the extension document. This policy is
described in more detail at
    https://www.khronos.org/registry/OpenGL/docs/update_policy.php

Ratified by the Khronos BOP, July 31, 2009.

Date: 05/19/2009  Version 1.0

OpenGL ES Extension #2

Written based on the wording of the OpenGL ES 1.1 specification.

Blending capability is extended by defining a function that allows
independent setting of the RGB and alpha blend factors for blend
operations that require source and destination blend factors.  It
is not always desired that the blending used for RGB is also applied
to alpha.

void BlendFuncSeparateOES(enum sfactorRGB,
                          enum dfactorRGB,
                          enum sfactorAlpha,
                          enum dfactorAlpha);

Accepted by the <pname> parameter of GetBooleanv, GetIntegerv, and
GetFloatv:

    BLEND_DST_RGB_OES                  0x80C8
    BLEND_SRC_RGB_OES                  0x80C9
    BLEND_DST_ALPHA_OES                0x80CA
    BLEND_SRC_ALPHA_OES                0x80CB

None

None

Replace the "Blend Equation" discussion in section 4.1.7 (Blending) with 
the following:

"The weighting factors used by the blend equation are determined by the
blend functions.  Blend functions are specified with the commands

    void BlendFuncSeparateOES(enum srcRGB, enum dstRGB, enum srcAlpha, enum dstAlpha);
    void BlendFunc(enum src, enum dst);
    
    BlendFuncSeparate arguments <srcRGB and dstRGB determine the source
and destination RGB blend functions, respectively, while <srcAlpha> and
<dstAlpha> determine the source and destination alpha blend functions.
BlendFunc argument <src> determines both the RGB and alpha source
functions, while <dst> determines both RGB and alpha destination functions.

    The possible source and destination blend functions and their
corresponding computed blend factors are summarized in table 4.blendfunc.

 Function                  RGB Blend Factors             Alpha Blend Factor
                           (Sr, Sg, Sb) or (Dr, Dg, Db)  Sa or Da
 ------------------        ----------------------------  ------------------
 ZERO                      (0, 0, 0)                     0
 ONE                       (1, 1, 1)                     1
 SRC_COLOR                 (Rs, Gs, Bs)                  As
 ONE_MINUS_SRC_COLOR       (1, 1, 1) - (Rs, Gs, Bs)      1 - As
 DST_COLOR                 (Rd, Gd, Bd)                  Ad
 ONE_MINUS_DST_COLOR       (1, 1, 1) - (Rd, Gd, Bd)      1 - Ad
 SRC_ALPHA                 (As, As, As)                  As
 ONE_MINUS_SRC_ALPHA       (1, 1, 1) - (As, As, As)      1 - As
 DST_ALPHA                 (Ad, Ad, Ad)                  Ad
 ONE_MINUS_DST_ALPHA       (1, 1, 1) - (Ad, Ad, Ad)      1 - Ad
 SRC_ALPHA_SATURATE (*1)   (f, f, f) (*2)                1

 Table 4.blendfunc: RGB and ALPHA source and destination blending functions
 and the corresponding blend factors.  Addition and subtraction of triplets
 is performed component-wise.
 
 *1 SRC_ALPHA_SATURATE is valid only for source RGB and alpha blending 
 functions.
 
 *2 f = min(As, 1 - Ad)."

In the "Blending State" paragraph, insert the following in place of
existing blend function state:

"The state required for blending is... four integers indicating the source 
and destination blend functions for RGB and alpha....  The initial state
for both source functions is ONE.  The initial state for both
destination functions is ZERO."

None

None

GL_INVALID_ENUM is generated if either sfactorRGB, dfactorRGB,
sfactorAlpha, or dfactorAlpha is not an accepted value.

The get values BLEND_SRC and BLEND_DST return the RGB source and
destination factor, respectively.

                                          Initial
Get Value             Get Command   Type  Value
---------             -----------   ----  -------
BLEND_SRC_RGB_OES     GetIntegerv   Z11   ONE
BLEND_DST_RGB_OES     GetIntegerv   Z10   ZERO
BLEND_SRC_ALPHA_OES   GetIntegerv   Z11   ONE
BLEND_DST_ALPHA_OES   GetIntegerv   Z10   ZERO

None

2009/05/19    Benj Lipchak    First draft of true extension specification