Created attachment 33382 [details]
test program

The swrast module does incorrect clipping of scan lines when they need to be clipped from the left side.

Attached is a small test program which shows one part of the problem, that is the color attribute not being correctly clipped.
But other attributes are not correctly clipped as well.
For example the fixed function texture 0 coordinate which was the original problem in a huger application.

Also attached is a patch originally against Mesa-7.5.2, but still valid for all versions in between up to mesa git of today.
This patch fixes all those problems that I could reproduce in our application as well as the attached example.
The patch just includes a 'monkey see - monkey do' change to correct all arrays in and attributes a SWspan by the leftClip amount of pixels.

Please apply or fix in a different way.

Thanks!

Mathias