Screen(‘BlendFunction’) applying different versions to different textures on the same screen

Programming Help
1

Hi, It seems like I need to use
Screen(‘BlendFunction’, win, ‘GL_SRC_ALPHA’, ‘GL_ONE_MINUS_SRC_ALPHA’) to create my grating properly in my code. I also want to use CreateProceduralGasussBlob function superimposed to my grating. However it seems like CreateProceduralGasussBlob requires me to use
Screen(‘BlendFunction’, win, GL_ONE, GL_ONE). Otherwise it doesn’t look like a Gaussian blob. Is there a way that I can use different parameters of Screen(‘BlendFunction’) for different textures at the same time on the same screen?
Thank you for the help!

2

It should work fine (I think) to call Screen(‘BlendFunction’,…) right before each place where you need to change it, give that a try.

Cheers,
Dee

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3

Yep, we do it all the time for displays that incorporate anti-aliased dots & procedural gabors.

There is some overhead in applying the Screen(‘BlendFunction’…) switch, so you’d just want to be sure to group all of your procedural drawing together, switch to GL_ONE, draw all your blobs, switch back to ‘alpha-one-minus-alpha’ — as opposed to toggling back & forth in a loop “1 grating, 1 dot, 1 grating, 1 dot, …”

e.g.

% must change blend function for procedural gabor rendering
% ...only one BlendFunction to set, not separate for each stereobuffer.
[prevSrcRect, prevDestRect] = Screen('BlendFunction', p.trial.display.ptr, 'GL_ONE', 'GL_ONE');
drawTheGabors(p, sn);
% reset previous blend functions
Screen('BlendFunction', p.trial.display.ptr, prevSrcRect, prevDestRect);

-Thad.

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4

Thank you for your response. Thad. This is really helpful!