The glBlendFunc function specifies pixel arithmetic for OpenGL rendering. Used to define how blend works.
glBlendFunc — specify pixel arithmetic
C Specification
void glBlendFunc( GLenum sfactor, GLenum dfactor); void glBlendFunci( GLuint buf, GLenum sfactor, GLenum dfactor); Parameters
buf For glBlendFunci, specifies the index of the draw buffer for which to set the blend function.
sfactor Specifies how the red, green, blue, and alpha source blending factors are computed. The initial value is GL_ONE.
dfactor Specifies how the red, green, blue, and alpha destination blending factors are computed. The following symbolic constants are accepted: GL_ZERO, GL_ONE, GL_SRC_COLOR, GL_ONE_MINUS_SRC_COLOR, GL_DST_COLOR, GL_ONE_MINUS_DST_COLOR, GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA, GL_DST_ALPHA, GL_ONE_MINUS_DST_ALPHA. GL_CONSTANT_COLOR, GL_ONE_MINUS_CONSTANT_COLOR, GL_CONSTANT_ALPHA, and GL_ONE_MINUS_CONSTANT_ALPHA. The initial value is GL_ZERO.
Description
Pixels can be drawn using a function that blends the incoming (source) RGBA values with the RGBA values that are already in the frame buffer (the destination values). Blending is initially disabled. Use glEnable and glDisable with argument GL_BLEND to enable and disable blending.
glBlendFunc defines the operation of blending for all draw buffers when it is enabled. glBlendFunci defines the operation of blending for a single draw buffer specified by buf when enabled for that draw buffer. sfactor specifies which method is used to scale the source color components. dfactor specifies which method is used to scale the destination color components. Both parameters must be one of the following symbolic constants: GL_ZERO, GL_ONE, GL_SRC_COLOR, GL_ONE_MINUS_SRC_COLOR, GL_DST_COLOR, GL_ONE_MINUS_DST_COLOR, GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA, GL_DST_ALPHA, GL_ONE_MINUS_DST_ALPHA, GL_CONSTANT_COLOR, GL_ONE_MINUS_CONSTANT_COLOR, GL_CONSTANT_ALPHA, GL_ONE_MINUS_CONSTANT_ALPHA, GL_SRC_ALPHA_SATURATE, GL_SRC1_COLOR, GL_ONE_MINUS_SRC1_COLOR, GL_SRC1_ALPHA, and GL_ONE_MINUS_SRC1_ALPHA. The possible methods are described in the following table. Each method defines four scale factors, one each for red, green, blue, and alpha. In the table and in subsequent equations, first source, second source and destination color components are referred to as Rs0Gs0Bs0As0, Rs1Gs1Bs1As1 and RdGdBdAd, respectively.
