[Mesa-dev] [PATCH] mesa: Don't clamp GetTexImage results post RGB->L if !ClampReadColor.

[Eric Anholt]

On Sat, 18 Jun 2011 17:43:16 -0700, Eric Anholt <eric at anholt.net> wrote:
> Fixes oglconform failure about our ARB_texture_float GetTexImage.
> Note that clamping does not appear in the "Conversion to L" stage of
> the GL 3.2 spec, and the next stage of "Final conversion" does
> clamping according to CLAMP_READ_COLOR.
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=36892

So, on further thought (after trying to build testcases), I'm not sure
what the correct answer is here.  Here's a bit I had in the test I was
writing:

+/** @file spec/arb_color_buffer_float/getteximage.c
+ *
+ * Tests that read color clamping affects glGetTexImage as
+ * specified by ARB_color_buffer_float.
+ *
+ * From page 373 of the GL 3.2 compatibility spec ("Texture Queries"):
+ *
+ *     "No pixel transfer operations are performed on this image, but
+ *      pixel storage modes that are applicable to ReadPixels are
+ *      applied."
+ *
+ * From page 313 of the GL 3.2 compatibility spec ("Final Conversion"):
+ *
+ *     "Read color clamping is controlled by calling ClampColor (see
+ *      section 3.7.5) with target set to CLAMP_READ_COLOR. If clamp
+ *      is TRUE, read color clamping is enabled; if clamp is FALSE,
+ *      read color clamping is disabled. If clamp is FIXED_ONLY, read
+ *      color clamping is enabled if the selected read color buffer
+ *      has fixed-point components."
+ *
+ * This step of ReadPixels is part of the "pixel storage modes" block
+ * in the diagram on page 309.  However, it doesn't make a lot of
+ * sense for reading of texture components to be clamped according to
+ * whether the color buffer has fixed-point components.  Let's
+ * interpret this as meaning clamping according to whether the texture
+ * storage has fixed-point components.  Also, the interpretation of
+ * read clamping applying to GetTexImage results means that before
+ * ARB_color_buffer_float, there was no way to GetTexImage the
+ * negative components of a snorm texture, which seems odd.
+ */

Anyone have any guidance here?
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