[Mesa-dev] [Bug 96518] [llvmpipe] piglit linestipple regression

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=96518

Jose Fonseca <jfonseca at vmware.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |brianp at vmware.com

--- Comment #2 from Jose Fonseca <jfonseca at vmware.com> ---
Althought generally FMA is more precise, it's possible that it give less
precise results.  Especially when dealing with things like whole integers, it's
quite possible that the lower precision of a non-fused MAD ends up "snapping"
things to the right values.  Whereas FMA preserves any intermediate rounding
error in the final result.


>From my POV, the issue is either:

- llvmpipe/draw stipple implementation needs better rounding (eg.g,
RoundToNearest as opposed to Truncate)

- the linestipple piglit test needs to be updated to not rely on precise
rounding of the stipple.


Either way I doubt the solution is to avoid FMA.

-- 
You are receiving this mail because:
You are the assignee for the bug.
You are the QA Contact for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.freedesktop.org/archives/mesa-dev/attachments/20160623/f1e0edf0/attachment.html>