Created attachment 92566 [details]
apitrace dump of this issue
The commit f5cfb4a is supposed to ignore the centroid flag, but it doesn't interpolate correctly when centroid is set.
Without the centroid flag, rendering is now fine, thank you :)
Posted a patch on mesa-dev mailing list to fix this issue:
[PATCH] i965: Ignore 'centroid' interpolation qualifier in case of persample shading
Please verify the fix.
This diff fixes my issue and the game now look much nicer. Thank you
fixed by dc2f94bc786768329973403248820a2e5249f102