## GL_ONE_MINUS_SRC_ALPHA

##### >Psychtoolbox>PsychAlphaBlending

constantString=GL_ONE_MINUS_SRC_ALPHA

Return the string ‘GL_ONE_MINUS_SRC_ALPHA’, which specifies an alpha

blending factor to Screen(‘BlendFunction’, …).

“Alpha” is a factor which weights RGB values when combining pixels by

drawing or copying. Alpha values weight the pixels drawn, the “source

surface”. Separate alpha values weight the pixels drawn onto, the

“destination surface”. A given pixel’s alpha factor is not necessarily

the alpha component of that pixel’s [rgba] color vector, but may instead

be the other combined surface’s alpha component, a function of either or

both both alpha compoenents, a constant, or it may derive from RGB values

of the other combined surface. The Psychtoolbox command

Screen(‘BlendFunction’) selects which. It implements the OpenGL function

“glBlendFunc”.

In MATLAB, Screen(‘BlendFunction’) accepts strings named for C constants

passed to the OpenGL function glBlendFunc().Enter “Help

PsychAlphaBlending” in the MATLAB command window for a list of blending

constants (and other functions related to alpha blending).

GL_ONE_MINUS_SRC_ALPHA may be used as either a source or a destination

factor.

see also: PsychAlphaBlending, AlphaDemo, AlphaBlendingTest.

`Psychtoolbox/PsychAlphaBlending/GL_ONE_MINUS_SRC_ALPHA.m`