[Bug 106601] The internal format RGB32F should be color-renderable for texture, But mesa can not support it

[bugzilla-daemon@freedesktop.org]

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https://bugs.freedesktop.org/show_bug.cgi?id=106601

--- Comment #12 from Yunchao He <yunchao.he@intel.com> ---
(In reply to Ilia Mirkin from comment #9)
> "Color-renderable" means "is it legal to use this format". It does NOT mean
> "the driver allows rendering to this format".

I am not a driver expert. But my understanding is that color-renderable means
that we can render into this format as a color buffer. If color-renderable
means "is it legal to use this format", then I can't explain these two
questions as follows: 
1. why we need to list that format which is illegal to use at all in spec? I
suppose there are many formats for graphics/video. Enumerating formats that are
not useful for texture (or renderbuffer) seems to be weird. 
2. If color-renderable(or renderable) means that "is it legal to use this
format" for a texture. Then that format is not allow to sample from. If so, how
to distinguish these two kinds of formats: 1) some formats can be supported by
a texture to sample only,  they can't be used to render into as a render target
via fbo, 2) some other formats can be supported by a texture to sample, and
render into as well.

The statement that "Color-renderable means is it legal to use this format. It
does NOT mean the driver allows rendering to this format" is correct for a
renderbuffer, but I think it is incorrect for a texture. Because a renderbuffer
is only used to render into, they can't be used to sample from. But this issue
is talking about texture, NOT renderbuffer. Maybe for the underlying
implementation, both texture and renderbuffer are mapped into the same GPU
memory (or even CPU memory), but from the perspective of users, texture and
renderbuffer are quite different.

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