[Mesa-dev] [PATCH 2/5] mesa: implement EXT_texture_shared_exponent

[Marek Olšák]

[snip]

> > +static INLINE float rgb9e5_MaxOf3(float x, float y, float z)
> > +{
> > +   if (x > y) {
> > +      return MAX2(x, z);
> > +   } else {
> > +      return MAX2(y, z);
> > +   }
> > +}
>
> On 04/26/2011 03:57 AM, Marek Olšák wrote:
> This could probably be a MAX3 macro defined in the same place as the
> existing MAX2 macro.  Also, why did you implement as you did instead of
>
>        MAX2(MAX2(x,y),z)
>
> Just curious...
>

It might be faster without common subexpression elimination. Not sure what
gcc can do. I haven't given it much thought.


> > diff --git a/src/mesa/main/texformat.c b/src/mesa/main/texformat.c
> > index cbebec9..3520f24 100644
> > --- a/src/mesa/main/texformat.c
> > +++ b/src/mesa/main/texformat.c
> > @@ -382,6 +382,16 @@ _mesa_choose_tex_format( struct gl_context *ctx,
> GLint internalFormat,
> >        }
> >     }
> >
> > +   if (ctx->Extensions.EXT_texture_shared_exponent) {
> > +      switch (internalFormat) {
> > +         case GL_RGB9_E5:
> > +            RETURN_IF_SUPPORTED(MESA_FORMAT_RGB9_E5_FLOAT);
>
> I could envision the extension being enabled but the format not being
> supported by the hardware.  This would be like the ARB_half_float_pixel
> code.  In this case, the fallbacks should be:
>
>   MESA_FORMAT_RGB_FLOAT16
>   MESA_FORMAT_RGBA_FLOAT16
>   MESA_FORMAT_RGB_FLOAT32
>   MESA_FORMAT_RGBA_FLOAT32
>
> The real question is if we ever want to enable any of these "extra
> format" extensions without requireing real hardware support.  If we
> don't, then these chases should assert that the format is supported.
>

I don't think it's useful to fake the format with some other one. It's like
RGTC: if hardware can't do it, let's disable it. RGB9_E5 is unsigned, and
faking the "unsignedness" in the texstore path for RGBA32F would be unfun.
Is there actually otherwise-GL3-capable hw which doesn't support it?

Marek
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