[Mesa-dev] [PATCH 05/12] i965/blorp: Skip redundant re-fast clear for non-compressed

[Topi Pohjolainen]

Originally re-clears where skipped but when lossless compression
was introduced the re-clears where errorneously enabled also for
non-compressed fast clears.

Signed-off-by: Topi Pohjolainen <topi.pohjolainen at intel.com>
CC: Ben Widawsky <benjamin.widawsky at intel.com>
CC: Kenneth Graunke <kenneth at whitecape.org>
CC: Harri Syrja <harri.syrja at intel.com>
Cc: Chad Versace <chad at kiwitree.net>
---
 src/mesa/drivers/dri/i965/brw_blorp.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_blorp.c b/src/mesa/drivers/dri/i965/brw_blorp.c
index 8a3caac..bc8513d 100644
--- a/src/mesa/drivers/dri/i965/brw_blorp.c
+++ b/src/mesa/drivers/dri/i965/brw_blorp.c
@@ -698,10 +698,23 @@ do_single_blorp_clear(struct brw_context *brw, struct gl_framebuffer *fb,
       const bool color_updated = brw_meta_set_fast_clear_color(
                                     brw, irb->mt, &ctx->Color.ClearColor);
 
-      /* If the buffer is already in INTEL_FAST_CLEAR_STATE_CLEAR, the clear
-       * is redundant and can be skipped.
+      /* If the buffer is already in INTEL_FAST_CLEAR_STATE_CLEAR, and the
+       * buffer isn't compressed, the clear is redundant and can be skipped.
+       *
+       * Without compression fast clear only operates on the mcs buffer
+       * recording if color values are cleared. The hardware, however,
+       * doesn't write the actual color value into the mcs or color
+       * buffer. Only by the time of render (inclucing color resolve) does the
+       * hardware read the _current_ color value in the surface state and
+       * write the actual pixel values in the color buffer accordingly.
+       *
+       * This seems to be the reason why sampler engine cannot handle
+       * non-compressed fast clear - it doesn't know how to read the color
+       * value from the surface state. With compression the color value is
+       * recorded in the color buffer (only not for every pixel) and therefore
+       * it is available without consulting the surface state.
        */
-      if (!color_updated &&
+      if ((!color_updated || !is_lossless_compressed) &&
           irb->mt->fast_clear_state == INTEL_FAST_CLEAR_STATE_CLEAR)
          return true;
 
-- 
2.5.5