Add alpha command line option.

src/nvtt/tools/compress.cpp

@@ -134,6 +134,7 @@ int main(int argc, char *argv[])
 	MyAssertHandler assertHandler;
 	MyMessageHandler messageHandler;
 
+	bool alpha = false;
 	bool normal = false;
 	bool color2normal = false;
 	bool wrapRepeat = false;
@@ -162,6 +163,10 @@ int main(int argc, char *argv[])
 		if (strcmp("-color", argv[i]) == 0)
 		{
 		}
+		else if (strcmp("-alpha", argv[i]) == 0)
+		{
+			alpha = true;
+		}
 		else if (strcmp("-normal", argv[i]) == 0)
 		{
 			normal = true;
@@ -295,13 +300,14 @@ int main(int argc, char *argv[])
 		printf("usage: nvcompress [options] infile [outfile]\n\n");
 		
 		printf("Input options:\n");
-		printf("  -color   \tThe input image is a color map (default).\n");
-		printf("  -normal  \tThe input image is a normal map.\n");
-		printf("  -tonormal\tConvert input to normal map.\n");
-		printf("  -clamp   \tClamp wrapping mode (default).\n");
-		printf("  -repeat  \tRepeat wrapping mode.\n");
-		printf("  -nomips  \tDisable mipmap generation.\n");
-		printf("  -premula \tPremultiply alpha into color channel.\n");
+		printf("  -color     \tThe input image is a color map (default).\n");
+		printf("  -alpha     \tThe input image has an alpha channel used for transparency.\n");
+		printf("  -normal    \tThe input image is a normal map.\n");
+		printf("  -tonormal  \tConvert input to normal map.\n");
+		printf("  -clamp     \tClamp wrapping mode (default).\n");
+		printf("  -repeat    \tRepeat wrapping mode.\n");
+		printf("  -nomips    \tDisable mipmap generation.\n");
+		printf("  -premula   \tPremultiply alpha into color channel.\n");
 		printf("  -mipfilter \tMipmap filter. One of the following: box, triangle, kaiser.\n\n");
 
 		printf("Compression options:\n");
@@ -426,6 +432,15 @@ int main(int argc, char *argv[])
 		inputOptions.setWrapMode(nvtt::WrapMode_Clamp);
 	}
 
+	if (alpha)
+	{
+		inputOptions.setAlphaMode(nvtt::AlphaMode_Transparency);
+	}
+	else
+	{
+		inputOptions.setAlphaMode(nvtt::AlphaMode_None);
+	}
+
 	if (normal)
 	{
 		setNormalMap(inputOptions);