[Mesa-dev] [PATCH] r300: Don't disable destination read if the src blend factor needs it

[Stefan Dösinger]

The read can remain disabled if the src alpha factor needs it because
the result would still be zero.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=57984

NOTE: This is a candidate for stable release branches.
---
 src/gallium/drivers/r300/r300_state.c |   12 ++++++++++--
 1 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/gallium/drivers/r300/r300_state.c b/src/gallium/drivers/r300/r300_state.c
index fba2d35..050c8f4 100644
--- a/src/gallium/drivers/r300/r300_state.c
+++ b/src/gallium/drivers/r300/r300_state.c
@@ -288,7 +288,11 @@ static void* r300_create_blend_state(struct pipe_context* pipe,
                          dstRGB == PIPE_BLENDFACTOR_ZERO) &&
                         (dstA == PIPE_BLENDFACTOR_SRC_COLOR ||
                          dstA == PIPE_BLENDFACTOR_SRC_ALPHA ||
-                         dstA == PIPE_BLENDFACTOR_ZERO)) {
+                         dstA == PIPE_BLENDFACTOR_ZERO) &&
+                        (srcRGB != PIPE_BLENDFACTOR_DST_COLOR &&
+                         srcRGB != PIPE_BLENDFACTOR_DST_ALPHA &&
+                         srcRGB != PIPE_BLENDFACTOR_INV_DST_COLOR &&
+                         srcRGB != PIPE_BLENDFACTOR_INV_DST_ALPHA)) {
                          blend_control |= R500_SRC_ALPHA_0_NO_READ;
                     }
 
@@ -297,7 +301,11 @@ static void* r300_create_blend_state(struct pipe_context* pipe,
                          dstRGB == PIPE_BLENDFACTOR_ZERO) &&
                         (dstA == PIPE_BLENDFACTOR_INV_SRC_COLOR ||
                          dstA == PIPE_BLENDFACTOR_INV_SRC_ALPHA ||
-                         dstA == PIPE_BLENDFACTOR_ZERO)) {
+                         dstA == PIPE_BLENDFACTOR_ZERO) &&
+                        (srcRGB != PIPE_BLENDFACTOR_DST_COLOR &&
+                         srcRGB != PIPE_BLENDFACTOR_DST_ALPHA &&
+                         srcRGB != PIPE_BLENDFACTOR_INV_DST_COLOR &&
+                         srcRGB != PIPE_BLENDFACTOR_INV_DST_ALPHA)) {
                          blend_control |= R500_SRC_ALPHA_1_NO_READ;
                     }
                 }
-- 
1.7.8.6