https://bugs.freedesktop.org/show_bug.cgi?id=25871

--- Comment #11 from Andreas Boll andreas.boll.dev@gmail.com 2012-09-12 13:56:46 UTC --- (In reply to comment #10)

It's so long ago I don't remember the exact details. You can easily figure it out though. The test program creates a 4x4 checker board texture and then uses a single point on it to draw the triangles. The range [0.25,0.5[ should all be the same color. The bug was that as you approached 0.5, it started sampling the next pixel prematurely.

So change the fragment program to use coordinate 0.4 or something like that. That colour should be the same as 0.4999... . Looking at the code, white seems to be the correct colour.

Ok I've got it.

With coordinate 0.4 I get a white color and with 0.4999 I get black.

Additionally I checked the other end of the range: Between the range [0.2480468676,0.498046860099] the color is white. If I change the fragment program to use coordinate 0.2480468675 then the color is black. With 0.4980468601 I get also black.

So the issue persists in git mesa master 9.1-devel (git-e81ee67)