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function constantString=GL_ONE
% constantString=GL_ONE
%
% Return the string 'GL_ONE', 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 may be used as either a source or a destination factor.
%
%
% see also: PsychAlphaBlending, AlphaDemo, AlphaBlendingTest.
constantString='GL_ONE';
return;
% HISTORY
%
% 2/9/05 awi Wrote it
% NOTES
%
% 2/9/05 awi These alpha blending factor functions are an excuse
% for documentation, but I don't see anytyhing wrong with that.
% By defining them as functions we get them to appear upon "Help
% PsychAlphBlendning", which is exaclty the right place to look.
% In MATLAB, There is a way to get help on a function. There is no way
% to get help on a string.
% All 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_SRC_ALPHA_SATURATE"
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