[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

Neil Roberts <neil at linux.intel.com> changed:

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--- Comment #4 from Neil Roberts <neil at linux.intel.com> 2012-02-26 09:11:06 PST ---
Created attachment 57666
  --> https://bugs.freedesktop.org/attachment.cgi?id=57666
readpix: Don't use the fast path for luminance types

When deciding whether to use the fast memcpy path for the fallback
implementation of glReadPixels, it now explicitly ignores luminance
types because in that case the conversion to and from RGB does not end
up with exactly the same values. Although it seems counter-intuitive,
the spec implies that even when the source and dest formats are a
luminance type, it will temporarily convert to RGB by storing the
luminance value in every component and then convert back to luminance
by adding all of the components together. This effectively means the
luminance values must be multiplied by three to conform to the spec.

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