tr_image: rework the alpha detection

Author: illwieckz

src/engine/renderer/tr_image.cpp

@@ -1053,32 +1053,42 @@ void R_UploadImage( const char *name, const byte **dataArray, int numLayers, int
 		internalFormat = GL_RGBA8;
 	}
 	else
+	{
+		// lightmap does not have alpha channel
+		if ( image->bits & IF_LIGHTMAP )
+		{
+			internalFormat = GL_RGB8;
+		}
+		else
+		{
+			internalFormat = GL_RGBA8;
+		}
+	}
+		
+	if ( internalFormat == GL_RGBA8 )
 	{
 		// scan the texture for each channel's max values
 		// and verify if the alpha channel is being used or not
 
 		c = image->width * image->height;
 		scan = dataArray[0];
 
-		// lightmap does not have alpha channel
-
 		// normalmap may have the heightmap in the alpha channel
 		// opaque alpha channel means no displacement, so we can enable
 		// alpha channel everytime it is used, even for normalmap
 
-		internalFormat = GL_RGB8;
+		bool hasAlpha = false;
 
-		if ( !( image->bits & IF_LIGHTMAP ) )
+		for ( i = 0; i < c * 4; i += 4 )
 		{
-			for ( i = 0; i < c; i++ )
+			if ( scan[ i + 3 ] != 255 )
 			{
-				if ( scan[ i * 4 + 3 ] != 255 )
-				{
-					internalFormat = GL_RGBA8;
-					break;
-				}
+				hasAlpha = true;
+				break;
 			}
 		}
+
+		internalFormat = hasAlpha ? GL_RGBA8 : GL_RGB8;
 	}
 
 	Log::Debug( "Uploading image %s (%d×%d, %d layers, %0#x type, %0#x format)", name, scaledWidth, scaledHeight, numLayers, image->type, internalFormat );