[Mesa-dev] classic driver cleanup: ChooseTexFormat

[Brian Paul]

On Fri, Sep 24, 2010 at 6:08 PM, Eric Anholt <eric at anholt.net> wrote:
> One of the uglier bits of the classic drivers, in my opinion, is the
> ChooseTexFormat hook.  Most drivers are trying to get to a similar set
> of formats, and using similar fallbacks for unavailable formats.
> Worse, they need to cleverly choose formats based on the incoming
> type/format to avoid having to munge the data on the way in if
> possible, and everyone needs to work those out.  So, rather than
> having each driver have these smarts, move it to the core.
>
> There are still some rough edges.  There are not enough fallbacks yet
> to cover everything (see i810 for example), so drivers with a more
> restricted set of supported formats may need to add more lines to
> _mesa_choose_tex_format.  Also, the endianness-dependent choice of
> formats in texmem.c and radeon's texturing isn't merged -- I knew I'd
> mess it up somehow if I did it on my own, so I'm leaving radeon for
> someone with big-endian to finish off.
>
> Any complaints, or should I go ahead and merge this?

In general this is a good clean-up.  A couple comments.

I see that you're merging the various format selections that the
drivers do back into core Mesa one driver at a time.  I guess that
would eventually cover all cases but there'll still be quite a few
holes.  For example, if a driver requests a GL_LUMINANCE internal
format but the driver has no native luminance texture formats, any
RGBA format will do as a fallback.  So after trying MESA_FORMAT_L8,
MESA_FORMAT_AL88, _AL88_REV etc., the various MESA_FORMAT_RGBA
permutations should be tried.

If you take a look at the st/mesa state tracker, a helper function
such as default_rgba_format() would help to fill in the holes.  Also
note how the Z/stencil formats are handled there.

Next, I think it's still worthwhile to keep using the user's
format/type info to help choose texture formats to try to hit the fast
paths in texstore.c for texture copying.

Lastly, I'd like to see ctx->texture_format_supported renamed
ctx->TextureFormatSupported to follow existing naming conventions.

Thanks.

-Brian