[PATCH 1/2] Check for empty vline ranges after clamping.

[Dave Witbrodt]

Kudos and thanks to Michel Dänzer for one or both of these:

   36c19067  Fix vline range calculations.
   bb0e1531  Check for empty vline ranges after clamping.

At first, I thought I was imagining things -- everything seemed
faster after building a new xf86-video-ati.  My previous build had been

   13b3aed4  EXA/r6xx+: fix rop setting for overlapping copies

which is the commit just before the latest ones, so my new build only 
involved the two commits mentioned above.  (I also left the other parts 
of the X stack unchanged:  libdrm, xorg-server, and mesa.  My kernel is 
3.2.4 + many cherry-picks from drm-fixes and drm-next, but when I built 
it today there was no immediate effect; the speed-up occurred only after 
the rebuild of the radeon driver.)

The 'torcs' game frame rate always varies over a wide range while 
playing -- normally 20 to 45 fps on my HD 5750 card, with occasional 
spikes into the 50' -- but now mostly stays well above 40 fps, usually 
in the upper 50's.  Since my monitor's refresh rate is only 60 Hz, the 
performance is now close to a level such that further improvements would 
make no visible difference (for me).

The 'prboom-plus' game has no fps indicator, but anyone could perceive 
the difference between the old and new radeon driver builds.  This is 
especially true if I maximize the view (hiding the dashboard) and play 
at fullscreen 1920x1200.  It's like I bought a new video card!  This 
particular program is now as responsive as it was with my NVidia GeForce 
7950 using the proprietary driver.  (That card died in the summer of 
2009, and I have been using only ATI/AMD cards since... and those only 
with the open source radeon driver.)


Thanks again,
Dave W.