r300: Don't disable destination read if the src blend factor needs it

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.

Signed-off-by: Marek Olšák <maraeo@gmail.com>
(cherry picked from commit ff5a9868c8d5041a3d944ce300c857934f4e8251)

diff --git a/src/gallium/drivers/r300/r300_state.c b/src/gallium/drivers/r300/r300_state.c
index 624847b..0467e91 100644 (file)
--- a/src/gallium/drivers/r300/r300_state.c
+++ b/src/gallium/drivers/r300/r300_state.c
@@ -287,7 +287,11 @@ 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;
                     }
 
@@ -296,7 +300,11 @@ 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;
                     }
                 }