[Intel-gfx] [intel-gfx][patch]fallback for 915/945 cubemap

[Eric Anholt]

On Mon, 2008-12-08 at 23:42 -0800, Keith Packard wrote:
> On Mon, 2008-12-08 at 22:47 -0800, Eric Anholt wrote:
> 
> > Ack for this one -- appears to be correct according to spec, and we
> > should expect everything to use CLAMP_TO_EDGE.
> 
> Ok, so do we have a 'fast mode' where we convert everything to
> CLAMP_TO_EDGE or do we just let apps suffer with fallbacks?

Apps should suffer for being dumb.  The spec tells you to do the two
modes we support:

"Should there be limits on the supported border modes for cube maps?

      RESOLUTION:  NO. The specificiation is written so that cube map
      texturing proceeds just like conventional 2D texture mapping once
      the face determination is made.

      Therefore, all OpenGL texture wrap modes should be supported though
      some modes are clearly inappropriate for cube maps.  The WRAP mode
      is almost certainly incorrect for cube maps.  Likewise, the CLAMP
      mode without a texture border is almost certainly incorrect for cube
      maps.  CLAMP when a texture border is present and CLAMP_TO_EDGE are
      both reasonably suited for cube maps.  Ideally, CLAMP with a texture
      border works best if the cube map edges can be replicated in the
      approriate texture borders of adjacent cube map faces.  In practice,
      CLAMP_TO_EDGE works reasonably well in most circumstances.

      Perhaps another extension could support a special cube map wrap
      mode that automatically wraps individual texel fetches to the
      appropriate adjacent cube map face.  The benefit from such a mode
      is small and the implementation complexity is involved so this wrap
      mode should not be required for a basic cube map texture extension."

We actually support the "special cube map wrap mode", but have no way to
expose it without creating a new extension or a driconf option.

-- 
Eric Anholt
eric at anholt.net                         eric.anholt at intel.com


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