[Bug 30007] [r300g] kwin thumbnails broken

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=30007

Marek Olšák <maraeo at gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED

--- Comment #38 from Marek Olšák <maraeo at gmail.com> 2011-01-04 13:31:44 PST ---
First some findings. The current implemention of thumbnails in kwin is strictly
targeted for GL3 hardware and should not work on GL2 hardware. This simple fact
can be seen from how the GLSL shader looks like and what features it uses (you
might also notice that the shader cannot be even ported to DirectX 9 without a
complete rewrite). However, the GLSL compiler in Mesa does something fglrx
didn't do: it lowers indirect addressing to conditional moves, but the cost is
such shaders end up being too long and therefore very slow. This is something
KDE people should fix if they want to ever compete with the performance of
other compositors. So far my impression from reading Kwin shaders isn't very
good and their shaders really need a broader review before getting accepted
unless Kwin is a toy project not suitable for every day use.

Commit 8543902bfbdfc15c39525bd99bee22e2f2126e74 fixes the Kwin thumbnails for
R5xx GPUs, but we can't really do anything with the speed.

One way to address this and other well-known performance issues with Kwin is to
refraing from using loops in GLSL shaders.

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