[PD] Blending modes v/s OpenGL

[Alexandre Quessy]

Hi all,
Anyone has a nice link to suggest me to understand well how we can
imitate the blending mode that we find in popular graphics programs
(such as Photoshop) like "burn", "add", "overlay" and such, using
different arguments to the OpenGL function glBlenFunc() ? It's pretty
well explained in the red book :
http://www.glprogramming.com/red/chapter06.html but I would like
something more straightforward. For instance, how can we imitate the
pretty complex "overlay" mode ?

Thanks,

-- 
Alexandre Quessy
http://alexandre.quessy.net
http://www.puredata.info/Members/aalex