intel: Fix emit_linear_blit to use DWORD aligned width blits

The width of the 2D blits used to copy the data is defined as a 16-bit
signed integer, but the pitch must be DWORD aligned. Limit to an integral
number of DWORDs, (1 << 15 - 4) rather than (1 << 15 -1).

Fixes corruption to data uploaded with glBufferSubData.

Signed-off-by: Peter Clifton <pcjc2@cam.ac.uk>

diff --git a/src/mesa/drivers/dri/intel/intel_blit.c b/src/mesa/drivers/dri/intel/intel_blit.c
index a74e217..7118898 100644 (file)
--- a/src/mesa/drivers/dri/intel/intel_blit.c
+++ b/src/mesa/drivers/dri/intel/intel_blit.c
@@ -483,8 +483,11 @@ intel_emit_linear_blit(struct intel_context *intel,
    /* Blits are in a different ringbuffer so we don't use them. */
    assert(intel->gen < 6);
 
-   /* The pitch is a signed value. */
-   pitch = MIN2(size, (1 << 15) - 1);
+   /* The pitch hits the GPU as a is a signed value, IN DWORDs.
+    * But we want width to match pitch. Max width is (1 << 15 - 1),
+    * rounding that down to the nearest DWORD is 1 << 15 - 4
+    */
+   pitch = MIN2(size, (1 << 15) - 4);
    height = size / pitch;
    ok = intelEmitCopyBlit(intel, 1,
                          pitch, src_bo, src_offset, I915_TILING_NONE,