[Mesa-dev] [PATCH] mesa/formats: Fix swizzle flipping for big-endian targets

[Jason Ekstrand]

The swizzle defines where in the format you should look for any given
channel.  When we flip the format around for BE targets, we need to change
the destinations of the swizzles, not the sources.  For example, say the
format is an RGBX format with a swizzle of xyz1 on LE.  Then it should be
wzy1 on BE;  however, the code as it was before, would have made it 1zyx on
BE which is clearly wrong.

Cc: Iago Toral <itoral at igalia.com>
Cc: Oded Gabbay <oded.gabbay at gmail.com>
---
 src/mesa/main/formats.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/src/mesa/main/formats.c b/src/mesa/main/formats.c
index d927073..27590ed 100644
--- a/src/mesa/main/formats.c
+++ b/src/mesa/main/formats.c
@@ -354,14 +354,22 @@ _mesa_array_format_flip_channels(mesa_array_format format)
       return format;
 
    if (num_channels == 2) {
-      _mesa_array_format_set_swizzle(&format, swizzle[1], swizzle[0],
-                                     swizzle[2], swizzle[3]);
+      /* Assert that the swizzle makes sense for 2 channels */
+      for (unsigned i = 0; i < 4; i++)
+         assert(swizzle[i] != 2 && swizzle[i] != 3);
+
+      static const uint8_t flip_xy[6] = { 1, 0, 2, 3, 4, 5 };
+      _mesa_array_format_set_swizzle(&format,
+                                     flip_xy[swizzle[0]], flip_xy[swizzle[1]],
+                                     flip_xy[swizzle[2]], flip_xy[swizzle[3]]);
       return format;
    }
 
    if (num_channels == 4) {
-      _mesa_array_format_set_swizzle(&format, swizzle[3], swizzle[2],
-                                     swizzle[1], swizzle[0]);
+      static const uint8_t flip[6] = { 3, 2, 1, 0, 4, 5 };
+      _mesa_array_format_set_swizzle(&format,
+                                     flip[swizzle[0]], flip[swizzle[1]],
+                                     flip[swizzle[2]], flip[swizzle[3]]);
       return format;
    }
 
-- 
2.4.3