[Mesa-dev] [PATCH 1/2] anv: allow blue in alpha component in swizzle for render

[Juan A. Suarez Romero]

In pre-Broadwell devices, as B4G4R4A4 is not supported natively, we
workaround it by using a format with a more complex swizzle, that uses
blue in alpha component.

Signed-off-by: Juan A. Suarez Romero <jasuarez at igalia.com>
---
 src/intel/vulkan/anv_private.h | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/src/intel/vulkan/anv_private.h b/src/intel/vulkan/anv_private.h
index 51e85c7..e9bf13c 100644
--- a/src/intel/vulkan/anv_private.h
+++ b/src/intel/vulkan/anv_private.h
@@ -1559,13 +1559,19 @@ static inline struct isl_swizzle
 anv_swizzle_for_render(struct isl_swizzle swizzle)
 {
    /* Sometimes the swizzle will have alpha map to one.  We do this to fake
-    * RGB as RGBA for texturing
+    * RGB as RGBA for texturing.
+    *
+    * It can have also alpha to blue. This happens to workaround support for
+    * B4G4R4A4 in gen < 8 devices, as this not supported natively.
     */
    assert(swizzle.a == ISL_CHANNEL_SELECT_ONE ||
-          swizzle.a == ISL_CHANNEL_SELECT_ALPHA);
+          swizzle.a == ISL_CHANNEL_SELECT_ALPHA ||
+          swizzle.a == ISL_CHANNEL_SELECT_BLUE);
 
-   /* But it doesn't matter what we render to that channel */
-   swizzle.a = ISL_CHANNEL_SELECT_ALPHA;
+   /* But it doesn't matter what we render to that channel, except for the
+    * B4G4R4A4 workaround */
+   if (swizzle.a == ISL_CHANNEL_SELECT_ONE)
+      swizzle.a = ISL_CHANNEL_SELECT_ALPHA;
 
    return swizzle;
 }
-- 
2.9.3