OES_blend_equation_separate

GL_OES_blend_equation_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: 06/17/2009  Version 1.1

OpenGL ES Extension #1

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

OES_blend_subtract is required for blend equation support.

OpenGL ES 1.1 provides a single blend equation that applies to both RGB
and alpha portions of blending.  This extension provides a separate blend 
equation for RGB and alpha to match the generality available for blend 
factors.

void BlendEquationSeparateOES(enum modeRGB, enum modeAlpha);

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

    BLEND_EQUATION_RGB_OES             0x8009 (same as BLEND_EQUATION_OES)
    BLEND_EQUATION_ALPHA_OES           0x883D

None

None

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

"Blending is controlled by the blend equations, defined by the commands

  void BlendEquationOES(enum mode);
  void BlendEquationSeparateOES(enum modeRGB, enum modeAlpha);

BlendEquationSeparateOES argument <modeRGB> determines the RGB blend
equation while <modeAlpha> determines the alpha blend equation.
BlendEquationOES argument <mode> determines both the RGB and alpha blend
equations.  <modeRGB> and <modeAlpha> must each be one of FUNC_ADD_OES,
FUNC_SUBTRACT_OES, or FUNC_REVERSE_SUBTRACT_OES.

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

Table 4.blendeq provides the corresponding per-component blend
equations for each mode, whether acting on RGB components for <modeRGB>
or the alpha component for <modeAlpha>.

In the table, the "s" subscript on a color component abbreviation
(R, G, B, or A) refers to the source color component for an incoming
fragment and the "d" subscript on a color component abbreviation refers
to the destination color component at the corresponding framebuffer
location.  A color component abbreviation without a subscript refers to
the new color component resulting from blending.  Additionally, Sr, Sg, 
Sb, and Sa are the red, green, blue, and alpha components of the source 
weighting factors determined by the source blend function, and Dr, Dg, Db,
and Da are the red, green, blue, and alpha components of the destination
weighting factors determined by the destination blend function.  Blend 
functions are described below.

Mode                   RGB components          Alpha component
---------------------  ----------------------  ----------------------
FUNC_ADD               Rc = Rs * Sr + Rd * Dr  Ac = As * Sa + Ad * Da
                       Gc = Gs * Sg + Gd * Dg
                       Bc = Bs * Sb + Bd * Db
---------------------  ----------------------  ----------------------
FUNC_SUBTRACT          Rc = Rs * Sr - Rd * Dr  Ac = As * Sa - Ad * Da
                       Gc = Gs * Sg - Gd * Dg
                       Bc = Bs * Sb - Bd * Db
---------------------  ----------------------  ----------------------
FUNC_REVERSE_SUBTRACT  Rc = Rd * Sr - Rs * Dr  Ac = Ad * Sa - As * Da
                       Gc = Gd * Sg - Gs * Dg
                       Bc = Bd * Sb - Bs * Db
---------------------  ----------------------  ----------------------

Table 4.blendeq:  RGB and alpha blend equations."

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

"The state required for blending is... two integers indicating the RGB
and alpha blend equations...  The initial blending equations for RGB and
alpha are FUNC_ADD_OES."

None

None

INVALID_ENUM is generated if either the modeRGB or modeAlpha
parameter of BlendEquationSeparateOES is not one of FUNC_ADD_OES,
FUNC_SUBTRACT_OES, or FUNC_REVERSE_SUBTRACT_OES.

                                             Initial
Get Value                 Get Command  Type  Value
------------------------  -----------  ----  ------------
BLEND_EQUATION_RGB_OES    GetIntegerv  Z     FUNC_ADD_OES
BLEND_EQUATION_ALPHA_OES  GetIntegerv  Z     FUNC_ADD_OES

[remove BLEND_EQUATION_OES from the table, add a note "BLEND_EQUATION_OES"
beside BLEND_EQUATION_RGB_OES to note the aliased name.]

None

2009/06/17    Benj Lipchak    Remove MIN/MAX from Table 4.blendeq
2009/05/19    Benj Lipchak    First draft of true extension specification