[Mesa-dev] [PATCH 1/2] intel/blorp: Swizzle clear colors on the CPU

[Jason Ekstrand]

It's trivial to swizzle clear colors on the CPU, easily deals with the
hardware restrictions for render target swizzles, and makes swizzled
clears work on all hardware as opposed to just HSW+.
---
 src/intel/blorp/blorp_clear.c | 48 +++++++++++++++++++++++++++----------------
 1 file changed, 30 insertions(+), 18 deletions(-)

diff --git a/src/intel/blorp/blorp_clear.c b/src/intel/blorp/blorp_clear.c
index 8ea22ac..4d63bbe 100644
--- a/src/intel/blorp/blorp_clear.c
+++ b/src/intel/blorp/blorp_clear.c
@@ -328,6 +328,26 @@ blorp_fast_clear(struct blorp_batch *batch,
    batch->blorp->exec(batch, &params);
 }
 
+static union isl_color_value
+swizzle_color_value(union isl_color_value src, struct isl_swizzle swizzle)
+{
+   union isl_color_value dst = { .u32 = { 0, } };
+
+   /* We assign colors in ABGR order so that the first one will be taken in
+    * RGBA precedence order.  According to the PRM docs for shader channel
+    * select, this matches Haswell hardware behavior.
+    */
+   if ((unsigned)(swizzle.a - ISL_CHANNEL_SELECT_RED) < 4)
+      dst.u32[swizzle.a - ISL_CHANNEL_SELECT_RED] = src.u32[3];
+   if ((unsigned)(swizzle.b - ISL_CHANNEL_SELECT_RED) < 4)
+      dst.u32[swizzle.b - ISL_CHANNEL_SELECT_RED] = src.u32[2];
+   if ((unsigned)(swizzle.g - ISL_CHANNEL_SELECT_RED) < 4)
+      dst.u32[swizzle.g - ISL_CHANNEL_SELECT_RED] = src.u32[1];
+   if ((unsigned)(swizzle.r - ISL_CHANNEL_SELECT_RED) < 4)
+      dst.u32[swizzle.r - ISL_CHANNEL_SELECT_RED] = src.u32[0];
+
+   return dst;
+}
 
 void
 blorp_clear(struct blorp_batch *batch,
@@ -346,6 +366,14 @@ blorp_clear(struct blorp_batch *batch,
    params.x1 = x1;
    params.y1 = y1;
 
+   /* Manually apply the clear destination swizzle.  This way swizzled clears
+    * will work for swizzles which we can't normally use for rendering and it
+    * also ensures that they work on pre-Haswell hardware which can't swizlle
+    * at all.
+    */
+   clear_color = swizzle_color_value(clear_color, swizzle);
+   swizzle = ISL_SWIZZLE_IDENTITY;
+
    if (format == ISL_FORMAT_R9G9B9E5_SHAREDEXP) {
       clear_color.u32[0] = float3_to_rgb9e5(clear_color.f32);
       format = ISL_FORMAT_R32_UINT;
@@ -353,24 +381,8 @@ blorp_clear(struct blorp_batch *batch,
       /* Broadwell and earlier cannot render to this format so we need to work
        * around it by swapping the colors around and using B4G4R4A4 instead.
        */
-
-      /* First, we apply the swizzle. */
-      union isl_color_value old;
-      assert((unsigned)(swizzle.r - ISL_CHANNEL_SELECT_RED) < 4);
-      assert((unsigned)(swizzle.g - ISL_CHANNEL_SELECT_RED) < 4);
-      assert((unsigned)(swizzle.b - ISL_CHANNEL_SELECT_RED) < 4);
-      assert((unsigned)(swizzle.a - ISL_CHANNEL_SELECT_RED) < 4);
-      old.u32[swizzle.r - ISL_CHANNEL_SELECT_RED] = clear_color.u32[0];
-      old.u32[swizzle.g - ISL_CHANNEL_SELECT_RED] = clear_color.u32[1];
-      old.u32[swizzle.b - ISL_CHANNEL_SELECT_RED] = clear_color.u32[2];
-      old.u32[swizzle.a - ISL_CHANNEL_SELECT_RED] = clear_color.u32[3];
-      swizzle = ISL_SWIZZLE_IDENTITY;
-
-      /* Now we re-order for the new format */
-      clear_color.u32[0] = old.u32[1];
-      clear_color.u32[1] = old.u32[2];
-      clear_color.u32[2] = old.u32[3];
-      clear_color.u32[3] = old.u32[0];
+      const struct isl_swizzle ARGB = ISL_SWIZZLE(ALPHA, RED, GREEN, BLUE);
+      clear_color = swizzle_color_value(clear_color, ARGB);
       format = ISL_FORMAT_B4G4R4A4_UNORM;
    }
 
-- 
2.5.0.400.gff86faf