GLAPI/glBlendEquationSeparate

glBlendEquationSeparate

Core in version		4.6
Core since version		2.0

glBlendEquationSeparate: set the RGB blend equation and the alpha blend equation separately

Function Definition

 void glBlendEquationSeparate(GLenum modeRGB, GLenum modeAlpha);
 void glBlendEquationSeparatei(GLuint buf, GLenum modeRGB, GLenum modeAlpha);

buf

for glBlendEquationSeparatei, specifies the index of the draw buffer for which to set the blend equations.

modeRGB

specifies the RGB blend equation, how the red, green, and blue components of the source and destination colors are combined. It must be GL_FUNC_ADD, GL_FUNC_SUBTRACT, GL_FUNC_REVERSE_SUBTRACT, GL_MIN, GL_MAX.

modeAlpha

specifies the alpha blend equation, how the alpha component of the 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 determines how a new pixel (the source color) is combined with a pixel already in the framebuffer (the destination color). These functions specifie one blend equation for the RGB-color components and one blend equation for the alpha component. glBlendEquationSeparatei specifies the blend equations for a single draw buffer whereas glBlendEquationSeparate sets the blend equations for all draw buffers.

The blend 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	$ {\begin{aligned}R_{r}&=s_{R}R_{s}+d_{R}R_{d}\\G_{r}&=s_{G}G_{s}+d_{G}G_{d}\\B_{r}&=s_{B}B_{s}+d_{B}B_{d}\end{aligned}} $	$ A_{r}=s_{A}A_{s}+d_{A}A_{d} $
GL_FUNC_SUBTRACT	$ {\begin{aligned}R_{r}&=s_{R}R_{s}-d_{R}R_{d}\\G_{r}&=s_{G}G_{s}-d_{G}G_{d}\\B_{r}&=s_{B}B_{s}-d_{B}B_{d}\end{aligned}} $	$ A_{r}=s_{A}A_{s}-d_{A}A_{d} $
GL_FUNC_REVERSE_SUBTRACT	$ {\begin{aligned}R_{r}&=d_{R}R_{d}-s_{R}R_{s}\\G_{r}&=d_{G}G_{d}-s_{G}G_{s}\\B_{r}&=d_{B}B_{d}-s_{B}B_{s}\end{aligned}} $	$ A_{r}=d_{A}A_{d}-s_{A}A_{s} $
GL_MIN	$ {\begin{aligned}R_{r}&=min(R_{s},R_{d})\\G_{r}&=min(G_{s},G_{d})\\B_{r}&=min(B_{s},B_{d})\end{aligned}} $	$ A_{r}=min(A_{s},A_{d}) $
GL_MAX	$ {\begin{aligned}R_{r}&=max(R_{s},R_{d})\\G_{r}&=max(G_{s},G_{d})\\B_{r}&=max(B_{s},B_{d})\end{aligned}} $	$ A_{r}=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 either modeRGB or modeAlpha is not one of GL_FUNC_ADD, GL_FUNC_SUBTRACT, GL_FUNC_REVERSE_SUBTRACT, GL_MAX, or GL_MIN.

GL_INVALID_VALUE is generated by glBlendEquationSeparatei if buf is greater than or equal to the value of GL_MAX_DRAW_BUFFERS.

Associated Gets

glGet with an argument of GL_BLEND_EQUATION_RGB

glGet with an argument of GL_BLEND_EQUATION_ALPHA

See Also

glGetString, glBlendColor, glBlendFunc, glBlendFuncSeparate

Copyright

Copyright © 2006 Khronos Group. This material may be distributed subject to the terms and conditions set forth in the Open Publication License, v 1.0, 8 June 1999. http://opencontent.org/openpub/.