1991-2006 Silicon Graphics, Inc.

glBlendEquation

3G

glBlendEquation

specify the equation used for both the RGB blend equation and the Alpha blend equation

# C Specification

                    void glBlendEquation
                    GLenum mode

## Parameters

`mode`

- specifies how source and destination colors are combined. It must be `GL_FUNC_ADD`, `GL_FUNC_SUBTRACT`, or `GL_FUNC_REVERSE_SUBTRACT`.

## Description

The blend equations determine how a new pixel (the ''source'' color) is combined with a pixel already in the framebuffer (the ''destination'' color). This function sets both the RGB blend equation and the alpha blend equation to a single equation.

These equations use the source and destination blend factors specified by either

glBlendFunc

or

glBlendFuncSeparate

. See

glBlendFunc

or

glBlendFuncSeparate

for a description of the various blend factors.

In the equations that follow, source and destination color components are referred to as R s G s B s A s and R d G d B d A d , respectively. The result color is referred to as R r G r B r A r . The source and destination blend factors are denoted s R s G s B s A and d R d G d B d A , respectively. For these equations all color components are understood to have values in the range 0 1 .

Mode | RGB Components | Alpha Component
`GL_FUNC_ADD` | Rr = R s ⁢ s R + R d ⁢ d R Gr = G s ⁢ s G + G d ⁢ d G Br = B s ⁢ s B + B d ⁢ d B | Ar = A s ⁢ s A + A d ⁢ d A
`GL_FUNC_SUBTRACT` | Rr = R s ⁢ s R - R d ⁢ d R Gr = G s ⁢ s G - G d ⁢ d G Br = B s ⁢ s B - B d ⁢ d B | Ar = A s ⁢ s A - A d ⁢ d A
`GL_FUNC_REVERSE_SUBTRACT` | Rr = R d ⁢ d R - R s ⁢ s R Gr = G d ⁢ d G - G s ⁢ s G Br = B d ⁢ d B - B s ⁢ s B | Ar = A d ⁢ d A - A s ⁢ s A

The results of these equations are clamped to the range 0 1 .

The `GL_FUNC_ADD` equation is useful for antialiasing and transparency, among other things.

Initially, both the RGB blend equation and the alpha blend equation are set to `GL_FUNC_ADD`.

## Errors

`GL_INVALID_ENUM` is generated if `mode` is not one of `GL_FUNC_ADD`, `GL_FUNC_SUBTRACT`, or `GL_FUNC_REVERSE_SUBTRACT`.

## Associated Gets

glGet

with an argument of `GL_BLEND_EQUATION_RGB`

glGet

with an argument of `GL_BLEND_EQUATION_ALPHA`

## See Also

glGetString

,

glBlendColor

,

glBlendEquationSeparate

,

glBlendFunc

glBlendFuncSeparate

## Copyright

Copyright 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.