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elezaza
02-25-2007, 11:11 AM
Hi,

I think it would be a great idee to add the way to use photoshop blending mode ... they are more and more popular ... or perhaps a blending programmable pipeline... It seems to be a very usefull things....
any comments ?

regards

zeoverlord
02-25-2007, 12:29 PM
Photoshop blending mode, no, it would be to complicated to implement.
Besides you can already implement most of it save for a few of them using glBlendFunc and glBlendEquation

programmable blending pipeline stage, yes please.

elezaza
02-25-2007, 12:41 PM
with glBlendFunc and glBlendEquation you can only implement a small number of photoshop mode... at the moment it seems that the only way to implement it is to use FBO to read the framebuffer and a pixel shader to blend the incoming fragment with the framebuffer.. trolltech use this way for example to add more blending mode ... (you can see that at http://zrusin.blogspot.com/2007/01/blend-modes-and-dash-offsets.html)...
but it's quite a lot of overhead just for a simple things !!! just add the needed glblendfunc to support all the common mode !!

Mikkel Gjoel
02-25-2007, 01:46 PM
elezaza - this is a hardware-feature so don't expect it to be added to OpenGL until hardware supports it.

The FBO-way does add overhead, but for a lot of applications utilizing strange blendmodes you would want to do it this way anyway.