Vasek Potocek napsal(a):
Dennis Kasprzyk napsal:
Am Samstag, 28. April 2007 15:35 schrieb Vasek Potocek:
Hello,
is there any way of utilizing OpenGL's depth test instead of the paint
order? If I understand it well, the aim here is to get it looking _like_
with depth test. I understand that shifting windows by an
"infinitesimal"
offset in the z direction would lead to various problems, but isn't is
possible to persuade OpenGL somehow to use different coordinate for the
depth test than for the perspective projection? (It would require a
little
bit more math than I outlined here, but should be possible.)
V.
For transparency effects you can't use a depth test, you have to paint
the whole screen from back to front.
Dennis
I'm sorry, I really forgot about the problem with transparency x depth
test. However, I still think this is soluble: what about using the
cubeCheckFTB function for deciding which glBlendFunc to use? Normally
we'd need to multiply the color drawn both by SRC_ALPHA and
ONE_MINUS_DST_ALPHA, which is not possible well enough, but thanks to
compiz' alpha-premultiply demand (fix me if it's not so), we could just
choose glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA); (as it is done now)
when drawing in front of all and glBlendFunc(GL_ONE_MINUS_DST_ALPHA,
GL_ONE); if drawing behind all. No other situation should arise in cube
+ 3D with BTF (and no other situation would be soluble at all even the
original way, however).
Sorry, this was inexact, forget it, please. Of course, the current code draws windows in a 1-2-3-6-5-4 order or so. What
is insoluble in both are more complex 3D effects which could cause windows for example intersect.
I hacked together a little demo showing this, see the attachment and
comments in it.
One problem I can see is this needs the support for alpha bitplanes,
which is not so automatic, could we rely on it in Linux implementations?
V.
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