[Mesa-dev] [PATCH 1/2] gallivm: implement seamless cube filtering

[Brian Paul]

On 10/18/2013 01:47 PM, sroland at vmware.com wrote:
> From: Roland Scheidegger <sroland at vmware.com>
>
> For seamless cube filtering it is necessary to determine new faces and new
> coords per sample. The logic for this is _seriously_ complex (what needs
> to happen is very "asymmetric" wrt face, x/y under/overflow), further
> complicated by the fact that if the 4 samples are in a corner (meaning we
> only have actually 3 samples, and all 3 are on different faces) then
> falling off the edge is happening _both_ on x and y axis simultaneously.
> There was a noticeable performance hit in mesa's cubemap demo when seamless
> filtering was forced on (just below 10 percent or so in a debug build, when
> disabling all filtering hacks, otherwise it would probably be a bit more) and
> when always doing the logic, hence use a branch which it only does it if any
> of the pixels in a quad (or in two quads) actually hit this. With that there
> was no measurable performance hit in the cubemap demo (neither in a debug nor
> release buidl), but this will vary (cubemap demo very rarely hits edges).
> Might also be different on other cpus, as this forces SoA sampling path which
> potentially can be quite a bit slower.
> Note that as for corners, this code gets all the 3 samples which actually
> exist right, and the 4th texel will simply be the same as one of the others,
> meaning that filter weights will be a bit wrong. This however should be
> enough for full OpenGL (but not d3d10) compliance.
> ---

That's some pretty dense code.  I doubt I could spot an error in it but 
it looks OK otherwise.

For both:
Reviewed-by: Brian Paul <brianp at vmware.com>