The ES and desktop GL specs diverge here.  Yay!

In desktop OpenGL, the driver can perform online compression of
uncompressed texture data.  GL_NUM_COMPRESSED_TEXTURE_FORMATS and
GL_COMPRESSED_TEXTURE_FORMATS give the application a list of formats
that it could ask the driver to compress with some expectation of
quality.  The GL_ARB_texture_compression spec calls this "suitable for
general-purpose usage."  As noted above, this means
GL_COMPRESSED_RGBA_S3TC_DXT1_EXT is not included in the list.

In OpenGL ES, the driver never performs compression.
GL_NUM_COMPRESSED_TEXTURE_FORMATS and GL_COMPRESSED_TEXTURE_FORMATS give
the application a list of formats that the driver can receive from the
application.  It is the *complete* list of formats.  The
GL_EXT_texture_compression_s3tc spec says:

    "New State for OpenGL ES 2.0.25 and 3.0.2 Specifications

        The queries for NUM_COMPRESSED_TEXTURE_FORMATS and
        COMPRESSED_TEXTURE_FORMATS include COMPRESSED_RGB_S3TC_DXT1_EXT,
        COMPRESSED_RGBA_S3TC_DXT1_EXT, COMPRESSED_RGBA_S3TC_DXT3_EXT,
        and COMPRESSED_RGBA_S3TC_DXT5_EXT."

Note that the addition is only to the OpenGL ES specification!

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
See-also: http://lists.freedesktop.org/archives/mesa-dev/2013-October/047439.html


Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
Cc: "10.0" <mesa-stable@lists.freedesktop.org>