Clarify the fact that we only optimize full buffer clears using fast
color clear, and why.
---
src/mesa/drivers/dri/i965/brw_blorp_clear.cpp | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/src/mesa/drivers/dri/i965/brw_blorp_clear.cpp
b/src/mesa/drivers/dri/i965/brw_blorp_clear.cpp
index 1904bde..3af22b6 100644
--- a/src/mesa/drivers/dri/i965/brw_blorp_clear.cpp
+++ b/src/mesa/drivers/dri/i965/brw_blorp_clear.cpp
@@ -238,7 +238,18 @@ brw_blorp_clear_params::brw_blorp_clear_params(struct
brw_context *brw,
}
}
- /* If we can do this as a fast color clear, do so. */
+ /* If we can do this as a fast color clear, do so.
+ *
+ * Note that the condition "!partial_clear" means we only try to do full
+ * buffer clears using fast color clear logic. This is necessary because
+ * the fast color clear alignment requirements mean that we typically have
+ * to clear a larger rectangle than (x0, y0) to (x1, y1). Restricting fast
+ * color clears to the full-buffer condition guarantees that the extra
+ * memory locations that get written to are outside the image boundary (and
+ * hence irrelevant). Note that the rectangle alignment requirements are
+ * never larger than the size of a tile, so there is no danger of
+ * overflowing beyond the memory belonging to the region.
+ */
if (irb->mt->mcs_state != INTEL_MCS_STATE_NONE && !partial_clear &&
wm_prog_key.use_simd16_replicated_data &&
is_color_fast_clear_compatible(brw, format, &ctx->Color.ClearColor)) {
--
1.8.4.2
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