[Mesa-dev] [PATCH] swr: perform perspective division on clip distances

[Rowley, Timothy O]

> On Nov 24, 2016, at 2:29 PM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
> 
> Clip distances need to be perspective-divided. This fixes all the
> interpolation-*-{distance,vertex} piglits.
> 
> Also take this opportunity to fix clip distances for points rasterized
> as triangles - the clip distance is not subject to sprite coord
> replacement, so there's no interpolation of it. We just take its value
> and put it in the "z" component of the barycentric-ready plane equation.
> (We could also just cull it at an earlier point in time, but that would
> require larger changes.)
> 

Would prefer this second change moved to a separate commit.  I’ve spent the most time looking at that, and still not convinced it’s correct.

> Signed-off-by: Ilia Mirkin <imirkin at alum.mit.edu>
> ---
> src/gallium/drivers/swr/rasterizer/core/binner.cpp | 22 +++++++++++++++-------
> 1 file changed, 15 insertions(+), 7 deletions(-)
> 
> diff --git a/src/gallium/drivers/swr/rasterizer/core/binner.cpp b/src/gallium/drivers/swr/rasterizer/core/binner.cpp
> index 6f9259f..d5f2e97 100644
> --- a/src/gallium/drivers/swr/rasterizer/core/binner.cpp
> +++ b/src/gallium/drivers/swr/rasterizer/core/binner.cpp
> @@ -383,7 +383,7 @@ PFN_PROCESS_ATTRIBUTES GetProcessAttributesFunc(uint32_t NumVerts, bool IsSwizzl
> /// @param clipDistMask - mask of enabled clip distances
> /// @param pUserClipBuffer - buffer to store results
> template<uint32_t NumVerts>
> -void ProcessUserClipDist(PA_STATE& pa, uint32_t primIndex, uint8_t clipDistMask, float* pUserClipBuffer)
> +void ProcessUserClipDist(PA_STATE& pa, uint32_t primIndex, uint8_t clipDistMask, float *pRecipW, float* pUserClipBuffer)
> {
>     DWORD clipDist;
>     while (_BitScanForward(&clipDist, clipDistMask))
> @@ -407,11 +407,12 @@ void ProcessUserClipDist(PA_STATE& pa, uint32_t primIndex, uint8_t clipDistMask,
> 
>         // setup plane equations for barycentric interpolation in the backend
>         float baryCoeff[NumVerts];
> +        float last = vertClipDist[NumVerts - 1] * pRecipW[NumVerts - 1];
>         for (uint32_t e = 0; e < NumVerts - 1; ++e)
>         {
> -            baryCoeff[e] = vertClipDist[e] - vertClipDist[NumVerts - 1];
> +            baryCoeff[e] = vertClipDist[e] * pRecipW[e] - last;
>         }
> -        baryCoeff[NumVerts - 1] = vertClipDist[NumVerts - 1];
> +        baryCoeff[NumVerts - 1] = last;
> 
>         for (uint32_t e = 0; e < NumVerts; ++e)
>         {
> @@ -834,7 +835,7 @@ endBinTriangles:
>         {
>             uint32_t numClipDist = _mm_popcnt_u32(rastState.clipDistanceMask);
>             desc.pUserClipBuffer = (float*)pArena->Alloc(numClipDist * 3 * sizeof(float));
> -            ProcessUserClipDist<3>(pa, triIndex, rastState.clipDistanceMask, desc.pUserClipBuffer);
> +            ProcessUserClipDist<3>(pa, triIndex, rastState.clipDistanceMask, &desc.pTriBuffer[12], desc.pUserClipBuffer);
>         }
> 
>         for (uint32_t y = aMTTop[triIndex]; y <= aMTBottom[triIndex]; ++y)
> @@ -1184,8 +1185,15 @@ void BinPoints(
>             if (rastState.clipDistanceMask)
>             {
>                 uint32_t numClipDist = _mm_popcnt_u32(rastState.clipDistanceMask);
> -                desc.pUserClipBuffer = (float*)pArena->Alloc(numClipDist * 2 * sizeof(float));
> -                ProcessUserClipDist<2>(pa, primIndex, rastState.clipDistanceMask, desc.pUserClipBuffer);
> +                desc.pUserClipBuffer = (float*)pArena->Alloc(numClipDist * 3 * sizeof(float));
> +                float dists[8];
> +                float one = 1.0f;
> +                ProcessUserClipDist<1>(pa, primIndex, rastState.clipDistanceMask, &one, dists);
> +                for (uint32_t i = 0; i < numClipDist; i++) {
> +                    desc.pUserClipBuffer[3*i + 0] = 0.0f;
> +                    desc.pUserClipBuffer[3*i + 1] = 0.0f;
> +                    desc.pUserClipBuffer[3*i + 2] = dists[i];
> +                }
>             }
> 
>             MacroTileMgr *pTileMgr = pDC->pTileMgr;
> @@ -1396,7 +1404,7 @@ void BinPostSetupLines(
>         {
>             uint32_t numClipDist = _mm_popcnt_u32(rastState.clipDistanceMask);
>             desc.pUserClipBuffer = (float*)pArena->Alloc(numClipDist * 2 * sizeof(float));
> -            ProcessUserClipDist<2>(pa, primIndex, rastState.clipDistanceMask, desc.pUserClipBuffer);
> +            ProcessUserClipDist<2>(pa, primIndex, rastState.clipDistanceMask, &desc.pTriBuffer[12], desc.pUserClipBuffer);
>         }
> 
>         MacroTileMgr *pTileMgr = pDC->pTileMgr;
> -- 
> 2.7.3
>