Fragment Operations - Praise for OpenGL ES 30 Programming Guide - page 312

where f source and C source are the incoming fragment's scaling factor and color,
respectively. Likewise, f destination and C destination are the pixel's scaling factor and
color, and op is the mathematical operator for combining the scaled values.

The scaling factors are specified by calling either glBlendFunc or
glBlendFuncSeparate .

void glBlendFunc (GLenum sfactor, GLenum dfactor)

sfactor specifies the blending coefficient for the incoming fragment
dfactor specifies the blending coefficient for the destination pixel

void glBlendFuncSeparate (GLenum srcRGB , GLenum dstRGB ,
GLenum srcAlpha , GLenum dstAlpha )

srcRGB specifies the blending coefficient for the incoming fragment's
red, green, and blue components
dstRGB specifies the blending coefficient for the destination pixel's
red, green, and blue components
srcAlpha specifies the blending coefficient for the incoming fragment's
alpha value
dstAlpha specifies the blending coefficient for the destination pixel's
alpha value

The possible values for the blending coefficients are shown in Table 11-3.

Table 11-3 Blending Functions

Alpha Blending

Blending Coefficient Enum RGB Blending Factors Factor

GL_ZERO

(0, 0, 0) 0

GL_ONE

(1, 1, 1) 1

GL_SRC_COLOR

( R s , G s , B s ) A s

GL_ONE_MINUS_SRC_COLOR

(1 - R s , 1 - G s , 1 - B s ) 1 - A s

GL_SRC_ALPHA

( A s , A s , A s ) A s

GL_ONE_MINUS_SRC_ALPHA

(1 - A s , 1 - A s , 1 - A s ) 1 - A s