[Mesa-dev] [Bug 46631] It's really hard to hit the fast path for the fallback glReadPixels code

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=46631

--- Comment #1 from Neil Roberts <neil at linux.intel.com> 2012-02-25 17:44:51 PST ---
Created attachment 57646
  --> https://bugs.freedesktop.org/attachment.cgi?id=57646
readpix: Don't disable fast path for normalized types

Mesa has a fast path for the generic fallback when using glReadPixels
for RGBA data which uses memcpy. However it was really difficult to
hit this case because it would not be used if any transferOps are
enabled. Any type apart from floating point or non-normalized integer
types (so any of the common types) would force enabling clamping so
the fast path could not be used. This patch makes it ignore clamping
when determining whether to use the fast path if the data type of the
buffer is an unsigned normalized type because in that case clamping
will not have any effect anyway.

This patch additionally makes it explicitly ignore luminance types
because in that case the conversion to and from RGB does not end up
with exactly the same values.

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