http://bugs.freedesktop.org/show_bug.cgi?id=25871
Summary: nearest neighbour samples wrong texel
(precision/rounding problem)
Product: Mesa
Version: git
Platform: Other
OS/Version: All
Status: NEW
Severity: normal
Priority: medium
Component: Drivers/DRI/R600
AssignedTo: [email protected]
ReportedBy: [email protected]
The following fragment program does the wrong thing on r600/r700 hardware:
TEX result.color, 0.498046860099, texture[0], 2D;
(the texture coord is as far as I got before I got bored. I'm not sure the
precision goes much further anyway)
The circumstances is that I have a 4x4 texture with nearest neighbour
interpolation. The above code should be sampling texel 1,1 but is instead
sampling texel 2,2. This causes problems for fragment programs that try to do
things based on texel coords (like bicubic interpolation).
This seems to be a hw bug as I've tried it with fglrx (albeit with a slightly
different card) and it exhibits the same bug. As such, I'm not sure it can be
solved but hopefully there is a workaround.
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