Manpages OpenGL - glBlendEquation

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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`	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.

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