The blend equation determines how a new pixel (the "source" color) is combined with a pixel already in the framebuffer (the "destination" color).
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 (Rs,Gs,Bs,As) and (Rd,Gd,Bd,Ad) respectively. The result color is referred to as (Rr,Gr,Br,Ar). The source and destination blend factors are denoted (sR,sG,sB,sA) and (dR,dG,dB,dA), respectively. For these equations all color components are understood to have values in the range [0,1].
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,RssR+RddR) |
Gr=min(1,GssG+GddG) |
Br=min(1,BssB+BddB) |
Ar=min(1,AssA+AddA) |
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=min(0,RssR−RddR) |
Gr=min(0,GssG−GddG) |
Br=min(0,BssB−BddB) |
Ar=min(0,AssA−AddA) |
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=min(0,RddR−RssR) |
Gr=min(0,GddG−GssG) |
Br=min(0,BddB−BssB) |
Ar=min(0,AddA−AssA) |
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.