Fix DXT1a single color compressor. Compare alpha against 0 instead of 128. Fixes issue 134.

ChangeLog

@@ -4,6 +4,7 @@ NVIDIA Texture Tools version 2.0.9
  * Fix the C wrapper and provide methods involving callbacks.
  * Improve C# / .NET Wrapper
  * Add an XNA Game Studio 3.1 Content Processor to make it easy to utilize NVIDIA Texture Tools in XNA applications.
+ * Fix single color DXT1a compressor. Fixes issue 134.
  
 NVIDIA Texture Tools version 2.0.8
  * Fix float to fixed image conversion. Patch provided by Alex Pfaffe. Fixes issue 121.

src/nvtt/CompressDXT.cpp

@@ -255,7 +255,7 @@ void nv::SlowCompressor::compressDXT1a(const CompressionOptions::Private & compr
 			
 			for (uint i = 0; i < 16; i++)
 			{
-				if (rgba.color(i).a < 128) anyAlpha = true;
+				if (rgba.color(i).a == 0) anyAlpha = true;
 				else allAlpha = false;
 			}
 			

src/nvtt/OptimalCompressDXT.cpp

@@ -205,7 +205,7 @@ void OptimalCompress::compressDXT1(Color32 c, BlockDXT1 * dxtBlock)
 
 void OptimalCompress::compressDXT1a(Color32 rgba, BlockDXT1 * dxtBlock)
 {
-	if (rgba.a < 128)
+	if (rgba.a == 0)
 	{
 		dxtBlock->col0.u = 0;
 		dxtBlock->col1.u = 0;

src/nvtt/QuickCompressDXT.cpp

@@ -483,7 +483,7 @@ 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

@@ -419,6 +419,11 @@ int main(int argc, char *argv[])
 			//	compressionOptions.setPixelFormat(16, 0, 0, 0);
 		}
 	}
+
+    if (format == nvtt::Format_BC1a) {
+        compressionOptions.setQuantization(false, true, true, 127);
+    }
+
 	if (fast)
 	{
 		compressionOptions.setQuality(nvtt::Quality_Fastest);