freedreno/a3xx: fix alpha-blending on RGBX formats

Expert debugging assistance provided by Chris Forbes.

Signed-off-by: Ilia Mirkin <[email protected]>
Reviewed-by: Rob Clark <[email protected]>

1 files changed, 25 insertions, 0 deletions

diff --git a/src/gallium/auxiliary/util/u_blend.h b/src/gallium/auxiliary/util/u_blend.h
new file mode 100644
index 00000000000..2485c34d418
--- /dev/null
+++ b/src/gallium/auxiliary/util/u_blend.h
@@ -0,0 +1,25 @@
+#ifndef U_BLEND_H
+#define U_BLEND_H
+
+#include "pipe/p_state.h"
+
+/**
+ * When faking RGBX render target formats with RGBA ones, the blender is still
+ * supposed to treat the destination's alpha channel as 1 instead of the
+ * garbage that's there. Return a blend factor that will take that into
+ * account.
+ */
+static INLINE int
+util_blend_dst_alpha_to_one(int factor)
+{
+   switch (factor) {
+   case PIPE_BLENDFACTOR_DST_ALPHA:
+      return PIPE_BLENDFACTOR_ONE;
+   case PIPE_BLENDFACTOR_INV_DST_ALPHA:
+      return PIPE_BLENDFACTOR_ZERO;
+   default:
+      return factor;
+   }
+}
+
+#endif /* U_BLEND_H */