[PATCH v4 1/7] d3dx{9,10}: Add a tweak to stb_dxt to more closely match native output.

[Connor McAdams]

From: Connor McAdams

This tweak helps us to more closely match the output of native
d3dx's DXT compression, which helps with d3dx10 tests.

Signed-off-by: Connor McAdams 
---
 dlls/d3dx9_36/stb_dxt.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/dlls/d3dx9_36/stb_dxt.h b/dlls/d3dx9_36/stb_dxt.h
index c25f6b015da..5f60a2a73b0 100644
--- a/dlls/d3dx9_36/stb_dxt.h
+++ b/dlls/d3dx9_36/stb_dxt.h
@@ -565,6 +565,16 @@ static void stb__CompressAlphaBlock(unsigned char *dest,unsigned char *src, int
    dest[1] = (unsigned char)mn;
    dest += 2;

+   /*
+    * Wine specific tweak to more closely match native behavior: If
+    * max is equal to minimum, just set all bits to 0 (which means the value
+    * is the value of max in this case).
+    */
+   if (mx == mn) {
+      memset(dest, 0, 6);
+      return;
+   }
+
    // determine bias and emit color indices
    // given the choice of mx/mn, these indices are optimal:
    // http://fgiesen.wordpress.com/2009/12/15/dxt5-alpha-block-index-determination...