i915: FBO performance

Thomas Zimmermann tdz at users.sourceforge.net
Fri Oct 2 12:42:18 PDT 2009

Hi there,

lately I've been playing around with OpenGL framebuffer objects while
trying out shadow mapping with GL. The FBO is thereby used to render
depth values to a texture, which is later needed for shadowing.

When I attach renderbuffer objects or texture objects that have ~1000
pixel per dimension to the framebuffer object, the framerate is ~160
fps. However, in the range between 1009 to 1024 pixels per dimension,
the performance drops to ~35 fps. For higher numbers of pixels (>=1025)
the performance again goes up to ~160 fps.

I've searched bugzilla and the ML archive for this, but haven't found
anything. Also, the changelogs of the intel driver releases 2.8 and 2.9
do not seem to contain any related entries.

I'm on a system with a Core2 Duo x64-64, and an Intel 945 graphics chip.
My distribution is an up-to-date Fedora 11, with Intel's xorg graphics
driver 2.7.

Best regards, Thomas

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