Merge fix for issue 134 into trunk.

src/nvtt/CompressorDX9.cpp

@@ -132,7 +132,7 @@ void NormalCompressorDXT1a::compressBlock(ColorBlock & rgba, nvtt::AlphaMode alp
     uint alphaMask = 0;
 	for (uint i = 0; i < 16; i++)
 	{
-		if (rgba.color(i).a < 128) alphaMask |= (3 << (i * 2)); // Set two bits for each color.
+		if (rgba.color(i).a == 0) alphaMask |= (3 << (i * 2)); // Set two bits for each color.
 	}
 
 	const bool isSingleColor = rgba.isSingleColor();

src/nvtt/QuickCompressDXT.cpp

@@ -533,7 +533,7 @@ void QuickCompress::compressDXT1a(const ColorBlock & rgba, BlockDXT1 * dxtBlock)
 	
 	for (uint i = 0; i < 16; i++)
 	{
-		if (rgba.color(i).a < 128) {
+		if (rgba.color(i).a == 0) {
 			hasAlpha = true;
 			break;
 		}

src/nvtt/tools/compress.cpp

@@ -482,8 +482,11 @@ int main(int argc, char *argv[])
         // Dither alpha when using BC2.
         compressionOptions.setQuantization(false, true, false);
     }
-
-    if (format == nvtt::Format_RGBA)
+    else if (format == nvtt::Format_BC1a) {
+        // Binary alpha when using BC1a.
+        compressionOptions.setQuantization(false, true, true, 127);
+    }
+    else if (format == nvtt::Format_RGBA)
     {
         if (luminance)
         {