[Mesa-dev] i965 fast depth clears

[Eric Anholt]

I finally got around to fixing my fast depth clear hack, and it turns
out it's a good payoff.  Here's the summary:

    Improves citybench high-res performance 3.0% +- 0.4%, n=10.
    Improves Lightsmark 1024x768 performance 0.74% +/- 0.20% (n=78).
    No significant difference on openarena (n=5, didn't fast clear) or
    nexuiz (n=3).

Check out the comment in brw_clear.c at the end for an interesting
explanation of how fast clears are implemented in hardware.  It sure
would have saved me time if they had explained that in the spec
instead of the restrictions that that leads to.