[Mesa-dev] Removing ARB_imaging subset extensions

Eric Anholt eric at anholt.net
Mon Sep 20 10:12:43 PDT 2010

On Mon, 20 Sep 2010 07:14:09 -0700, Ian Romanick <idr at freedesktop.org> wrote:
> Hash: SHA1
> Eric Anholt wrote:
> > On our way to OpenGL 3.0, it would be nice to clean out some of the
> > optional deprecated features that Mesa supports.  The ARB_imaging subset
> > is the highest on my list -- it significantly clutters up the pixel
> > path, and has always been optional even though the specification text
> > got rolled into OpenGL 1.2.  ATI's proprietary driver never supported
> > the imaging subset, and what I've read of NVIDIA's implementation
> > online, its presence is a user trap.  Keeping an implementation of it is
> > not helping our users from a performance or portability perspective.
> > 
> > I've pushed a branch to my repo removing most of SGI_color_matrix,
> > SGI_color_table, EXT_histogram, and EXT_convolution.  Here's the
> > diffstat:
> [snip]
> > That's 2.7% of mesa/main/, and driver size dropped correspondingly.
> > Note that we don't get to completely drop histogram.c and convolve.c, as
> > we're supposed to have the entrypoints and just emit INVALID_OPERATION
> > for the missing extensions even if the ARB_imaging subset isn't present.
> > 
> > If we don't have any strong justification for keeping this code, I'd
> > like to merge this to master.
> I will probably push a similar branch this week that removes other
> extensions discussed at XDS.  See "kill it with fire" at the bottom of
> http://www.x.org/wiki/Events/XDS2010/Program.  It looks like the biggest
> savings will come from removing GL_EXT_paletted_texture and
> GL_EXT_shared_texture_palette.

I was concerned about the texture palette ones since several apps show
an interest in them, but now that I go back and look at the docs we
couldn't support these in our hardware, since 915 and 965 have a single
shared texture palette (or for g45+, two), and
GL_EXT_shared_texture_palette is an extension to the general extension
to use a shared texture palette optionally, rather than an alternative
that matches our hardware support.  I can't even find palette support in
r5xx or r6xx.  Presumably people would just do this with dependent
texture lookups at this point.
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