On 03/16/2013 10:09 AM, Eric Anholt wrote:
Kenneth Graunke <kenn...@whitecape.org> writes:
On 03/15/2013 04:54 PM, Eric Anholt wrote:
Kenneth Graunke <kenn...@whitecape.org> writes:
Commit 33599433c7 began setting the texture swizzle mode to XYZ1 for
RED, RG, and RGB textures in order to force alpha to 1.0 in case we
actually stored the texture as RGBA.
This had a unforseen performance implication: the shader precompile
assumes that the texture swizzle mode will be XYZW for non-shadow
sampler types. By setting it to XYZ1, this means every shader used with
a RED, RG, or RGB texture has to be recompiled. This is a very common
case.
Unfortunately, there's no way to improve the precompile, since RGBA
textures still need XYZW, and there's no way to know by looking at
the shader source what texture formats might be used.
However, we only need to smash alpha to 1.0 if the texture's memory
format actually has alpha bits. If not, the sampler already returns 1.0
for us without any special swizzling. XRGB8888, for example, is a very
common case where this occurs.
This partially fixes a performance regression since commit 33599433c7.
More work is required to fully fix it in all cases. This at least helps
Warsow.
Now that we have MESA_FORMAT_XBGR16161616_FLOAT and company, we could
potentially make this conditional just die by using those formats.
Absolutely - I believe the real fix is to use XRGB formats when
sampling, and ARGB formats when rendering. I'm pretty sure we have
formats for all of those now. We should do that.
In the meantime, this patch improves things and is simple and easily
cherry-pickable...
Fair enough. Are there some big performance changes?
No, not large in terms of FPS. Generally, when we get this wrong, we
recompile each shader once and then it's right from then on. It does
reduce stuttering quite a bit, though, since it means we don't have to
recompile on first draw. I suppose it might affect very short demos.
--Ken
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