glBlendEquation

Name

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, GL_FUNC_REVERSE_SUBTRACT, GL_MIN, GL_MAX.

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.

Calling this function is equivalent to calling glBlendEquationSeparate with modeRGB and modeAlpha both set to the value of mode.

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`	$Rr = R_{d} d_{R} - R_{s} s_{R}$ $Gr = G_{d} d_{G} - G_{s} s_{G}$ $Br = B_{d} d_{B} - B_{s} s_{B}$	$Ar = A_{d} d_{A} - A_{s} s_{A}$
`GL_MIN`	$Rr = \min (R_{s}, R_{d})$ $Gr = \min (G_{s}, G_{d})$ $Br = \min (B_{s}, B_{d})$	$Ar = \min (A_{s}, A_{d})$
`GL_MAX`	$Rr = \max (R_{s}, R_{d})$ $Gr = \max (G_{s}, G_{d})$ $Br = \max (B_{s}, B_{d})$	$Ar = \max (A_{s}, A_{d})$

The results of these equations are clamped to the range $[0, 1]$ .

The GL_MIN and GL_MAX equations are useful for applications that analyze image data (image thresholding against a constant color, for example). 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.

Notes

The GL_MIN, and GL_MAX equations do not use the source or destination factors, only the source and destination colors.

Errors

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

Associated Gets

glGet with an argument of GL_BLEND_EQUATION_RGB

glGet with an argument of GL_BLEND_EQUATION_ALPHA

API Version Support

	OpenGL ES API Version
Function Name	2.0	3.0	3.1
glBlendEquation	✔	✔	✔

Copyright

Copyright © 1991-2006 Silicon Graphics, Inc. Copyright © 2010-2014 Khronos Group. This document is licensed under the SGI Free Software B License. For details, see https://web.archive.org/web/20171022161616/http://oss.sgi.com/projects/FreeB/.

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