renderer: introduce and use IF_NOALPHA

Author: illwieckz

src/engine/renderer/tr_bsp.cpp

@@ -483,8 +483,8 @@ static void R_LoadLightmaps( lump_t *l, const char *bspName )
 		return;
 	}
 
-	int lightMapBits = IF_LIGHTMAP | IF_NOPICMIP;
-	int deluxeMapBits = IF_NORMALMAP | IF_NOPICMIP;
+	int lightMapBits = IF_LIGHTMAP | IF_NOALPHA | IF_NOPICMIP;
+	int deluxeMapBits = IF_NORMALMAP | IF_NOALPHA | IF_NOPICMIP;
 
 	if ( tr.worldLinearizeLightMap )
 	{

src/engine/renderer/tr_image.cpp

@@ -849,10 +849,13 @@ void R_UploadImage( const char *name, const byte **dataArray, int numLayers, int
 	int        mipWidth, mipHeight, mipLayers, mipSize, blockSize = 0;
 	int        i, c;
 	const byte *scan;
+
+	bool isSRGB = image->bits & IF_SRGB;
+	bool isAlpha = !( image->bits & IF_NOALPHA );
+
 	GLenum     target;
 	GLenum     format = GL_RGBA;
-	GLenum     internalFormat = GL_RGB;
-	bool isSRGB = image->bits & IF_SRGB;
+	GLenum internalFormat = isAlpha ? GL_RGBA : GL_RGB;
 
 	static const vec4_t oneClampBorder = { 1, 1, 1, 1 };
 	static const vec4_t zeroClampBorder = { 0, 0, 0, 1 };
@@ -1054,15 +1057,12 @@ void R_UploadImage( const char *name, const byte **dataArray, int numLayers, int
 	}
 	else
 	{
-		// lightmap does not have alpha channel
-		if ( image->bits & IF_LIGHTMAP )
-		{
-			internalFormat = GL_RGB8;
-		}
-		else
-		{
-			internalFormat = GL_RGBA8;
-		}
+		internalFormat = GL_RGBA8;
+	}
+
+	if ( internalFormat == GL_RGBA8 && !isAlpha )
+	{
+		internalFormat = GL_RGB8;
 	}
 
 	// Detect formats.

src/engine/renderer/tr_local.h

@@ -484,7 +484,8 @@ enum class ssaoMode {
 	  IF_BC4 = BIT( 22 ),
 	  IF_BC5 = BIT( 23 ),
 	  IF_RGBA32UI = BIT( 24 ),
-	  IF_HOMEPATH = BIT( 25 )
+	  IF_HOMEPATH = BIT( 25 ),
+	  IF_NOALPHA = BIT( 26 )
 	};
 
 	enum class filterType_t