swr/rast: enforce use of tile offsets

Reviewed-by: Bruce Cherniak <bruce.cherniak@intel.com>

src/gallium/drivers/swr/rasterizer/core/backend_impl.h

@@ -1056,6 +1056,7 @@ void BackendPixelRate(DRAW_CONTEXT*        pDC,
         {
             const bool useAlternateOffset = ((xx & SIMD_TILE_X_DIM) != 0);
 
+            psContext.alternateOffset = useAlternateOffset ? 1 : 0;
 
             simdscalar activeLanes;
             if (!(work.anyCoveredSamples & MASK))

src/gallium/drivers/swr/rasterizer/core/backend_sample.cpp

@@ -83,6 +83,7 @@ void BackendSampleRate(DRAW_CONTEXT*        pDC,
         {
             const bool useAlternateOffset = ((xx & SIMD_TILE_X_DIM) != 0);
 
+            psContext.alternateOffset = useAlternateOffset ? 1 : 0;
 
             if (T::InputCoverage != SWR_INPUT_COVERAGE_NONE)
             {

src/gallium/drivers/swr/rasterizer/core/backend_singlesample.cpp

@@ -84,6 +84,7 @@ void BackendSingleSample(DRAW_CONTEXT*        pDC,
         {
             const bool useAlternateOffset = ((xx & SIMD_TILE_X_DIM) != 0);
 
+            psContext.alternateOffset = useAlternateOffset ? 1 : 0;
 
             simdmask coverageMask = work.coverageMask[0] & MASK;
 

src/gallium/drivers/swr/rasterizer/core/state.h

@@ -380,6 +380,8 @@ struct SWR_PS_CONTEXT
 
     uint8_t* pColorBuffer[SWR_NUM_RENDERTARGETS]; // IN: Pointers to render target hottiles
 
+    uint32_t alternateOffset; // IN: for 8x2 tile backend, which 4x2 do we need to read from
+
     SWR_SHADER_STATS stats; // OUT: shader statistics used for archrast.
 };