https://bugs.freedesktop.org/show_bug.cgi?id=65416
Priority: medium
Bug ID: 65416
Assignee: dri-devel at lists.freedesktop.org
Summary: r300g does not eliminate unread varyings
Severity: normal
Classification: Unclassified
OS: All
Reporter: stefandoesinger at gmx.at
Hardware: Other
Status: NEW
Version: git
Component: Drivers/Gallium/r300
Product: Mesa
Created attachment 80344
--> https://bugs.freedesktop.org/attachment.cgi?id=80344&action=edit
Example shaders
r300g tries to interpolate varyings written by the vertex shader even if the
fragment shader does not read them. The attached program code illustrates this
with two sample shaders.
The shaders in question were generated by Wine's fixed function pipeline
replacement, generated from a fixed function setup set up by 3DMark 2000.
The visible issues caused by this are broken fog because the driver runs out of
varyings and reduced performance due to the extra shader instructions.
An argument could be made that this is Wine's bug, and it should not generate
such inefficient shaders. Doing this would be a major inconvenience though
because the vertex and fragment shader are generated independently. As far as I
can see the proprietary drivers optimize this inefficiency away.
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