http://bugs.freedesktop.org/show_bug.cgi?id=13395





------- Comment #5 from [EMAIL PROTECTED]  2007-11-28 05:45 PST -------
(In reply to comment #4)
> Brian, Ian, 
> Thanks for the comments. Please note, that I am referring to glTexSubImage2D()
> and not to glCompressedTexSubImage(), you cited in the reply.
The same restrictions can be found later in the error section for
TexSubImage2D.

> The extension specification says, as far as the former function is concerned,
> that the width, height *don't* have to ba a multiple of four, *if* xoffset =
> yoffset = 0:
>    * <width> is not a multiple of four or equal to TEXTURE_WIDTH, 
>       unless <xoffset> and <yoffset> are both zero.
> 
> I think the teximage.c:subtexture_error_check2(), called in glTexSubImage2D(),
> discriminates the above case. What is your opinion?
I think the EXT_texture_compression_s3tc specification contradicts the core
OpenGL specification. Such is life.
Core OpenGL mandates that there is no error, but texels outside the region
modified are undefined. The spec also mentions the restrictions may be lifted
by some compression formats. This is what EXT_texture_compression_s3tc does, so
texels outside the region are now defined, but only if your subtexture is
aligned properly. It does however introduce a new restriction (it needs to be
aligned or an error will happen), which seems to be against the core spec
(which would just leave the texels undefined but no error).
In any case, I guess going by the wording of the more specific extension is the
right thing to do, and anyway core spec wouldn't make it work as the texels
outside the modified region would be completely undefined which is likely just
as useless as an error.


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