GLBLENDEQUATION(3G)

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.

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 | <div> Rr = R s ⁢ s R + R d ⁢ d R </div> <div> Gr = G s ⁢ s G + G d ⁢ d G </div> <div> Br = B s ⁢ s B + B d ⁢ d B </div> | <div> Ar = A s ⁢ s A + A d ⁢ d A </div>
GL_FUNC_SUBTRACT | <div> Rr = R s ⁢ s R - R d ⁢ d R </div> <div> Gr = G s ⁢ s G - G d ⁢ d G </div> <div> Br = B s ⁢ s B - B d ⁢ d B </div> | <div> Ar = A s ⁢ s A - A d ⁢ d A </div>
GL_FUNC_REVERSE_SUBTRACT | <div> Rr = R d ⁢ d R - R s ⁢ s R </div> <div> Gr = G d ⁢ d G - G s ⁢ s G </div> <div> Br = B d ⁢ d B - B s ⁢ s B </div> | <div> Ar = A d ⁢ d A - A s ⁢ s A </div>
GL_MIN | <div> Rr = min ⁡ R s R d </div> <div> Gr = min ⁡ G s G d </div> <div> Br = min ⁡ B s B d </div> | <div> Ar = min ⁡ A s A d </div>
GL_MAX | <div> Rr = max ⁡ R s R d </div> <div> Gr = max ⁡ G s G d </div> <div> Br = max ⁡ B s B d </div> | <div> Ar = max ⁡ A s A d </div>

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.

GL_INVALID_OPERATION is generated if glBlendEquation is executed between the execution of glBegin() and the corresponding execution of glEnd().

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 © 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/.