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Manual Reference Pages  - GLBLENDEQUATION (3G)

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glBlendEquation - set the blend equation

CONTENTS

C Specification
Parameters
Description
Notes
Errors
Associated Gets
See Also

void glBlendEquation( GLenum mode )

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.

The blend equation determines how a new pixel (the ‘‘source’’ color) is combined with a pixel already in the framebuffer (the ‘‘destination’’ color).

GL_MIN	sets the blend equation so that each component of the result color is the minimum of the corresponding components of the source and destination colors.
GL_MAX	sets the blend equation so that each component of the result color is the maximum of the corresponding components of the source and destination colors.

The remaining blend equations use the source and destination blend factors specified by  glBlendFunc. See  glBlendFunc 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].

GL_FUNC_ADD
	sets the blend equation so that the source and destination data are added. Each component of the source color is multiplied by the corresponding source factor, then each component of the destination color is multiplied by the corresponding destination factor. The result is the componentwise sum of the two products, clamped to the range [0, 1]. Rr = min(1, Rs sR + Rd dR) Gr = min(1, Gs sG + Gd dG) Br = min(1, Bs sB + Bd dB) Ar = min(1, As sA + Ad dA)
GL_FUNC_SUBTRACT
	Is like  GL_FUNC_ADD except the product of the destination factor and the destination color is componentwise subtracted from the product of the source factor and the source color. The result is clamped to the range [0, 1]. Rr = max(0, Rs sR - Rd dR) Gr = max(0, Gs sG - Gd dG) Br = max(0, Bs sB - Bd dB) Ar = max(0, As sA - Ad dA)
GL_FUNC_REVERSE_SUBTRACT
	Is like  GL_FUNC_ADD except the product of the source factor and the source color is componentwise subtracted from the product of the destination factor and the destination color. The result is clamped to the range [0, 1]. Rr = max(0, Rd dR - Rs sR) Gr = max(0, Gd dG - Gs sG) Br = max(0, Bd dB - Bs sB) Ar = max(0, Ad dA - As sA)

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, the blend equation is set to  GL_FUNC_ADD.

 glBlendEquation is part of the  GL_ARB_imaging subset.  glBlendEquation is present only if  GL_ARB_imaging is returned when  glGetString is called with  GL_EXTENSIONS as its argument.

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

 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.

glGet with an argument of  GL_BLEND_EQUATION

 glGetString(3G),  glBlendColor(3G),  glBlendFunc(3G)

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