renderer: implement and detect RG images

Author: illwieckz

src/engine/renderer/tr_backend.cpp

@@ -742,8 +742,12 @@ static GLint GL_ToSRGB( GLint internalFormat, bool isSRGB )
 			/* EXT_texture_sRGB_R8 extension.
 			See: https://github.com/KhronosGroup/OpenGL-Registry/blob/main/extensions/EXT/EXT_texture_sRGB_R8.txt */
 			case GL_RED:
+			case GL_R8:
 				ASSERT( glConfig.textureSrgbR8Available );
 				return GL_SR8_EXT;
+			case GL_RG:
+				ASSERT( glConfig.textureSrgbRG8Available );
+				return GL_SRG8_EXT;
 			case GL_RGB:
 				return GL_SRGB;
 			case GL_RGBA:

src/engine/renderer/tr_image.cpp

@@ -177,10 +177,12 @@ class ListImagesCmd : public Cmd::StaticCmd
 			{ GL_RGBA32UI, { "RGBA32UI", 16 } },
 			{ GL_ALPHA16F_ARB, { "A16F", 2 } },
 			{ GL_ALPHA32F_ARB, { "A32F", 4 } },
+			{ GL_R8, { "R8", 1 } },
 			{ GL_R16F, { "R16F", 2 } },
 			{ GL_R32F, { "R32F", 4 } },
 			{ GL_LUMINANCE_ALPHA16F_ARB, { "LA16F", 4 } },
 			{ GL_LUMINANCE_ALPHA32F_ARB, { "LA32F", 8 } },
+			{ GL_RG8, { "RG8", 2 } },
 			{ GL_RG16F, { "RG16F", 4 } },
 			{ GL_RG32F, { "RG32F", 8 } },
 
@@ -946,6 +948,18 @@ void R_UploadImage( const char *name, const byte **dataArray, int numLayers, int
 			internalFormat = GL_RED;
 		}
 	}
+	else if ( image->bits & IF_RG )
+	{
+		if ( isSRGB && !glConfig.textureSrgbRG8Available )
+		{
+			Log::Warn("red-green image '%s' cannot be loaded as sRGB", image->name );
+			internalFormat = GL_RGB8;
+		}
+		else
+		{
+			internalFormat = GL_RG8;
+		}
+	}
 	else if ( image->bits & ( IF_RGBA16F | IF_RGBA32F | IF_TWOCOMP16F | IF_TWOCOMP32F | IF_ONECOMP16F | IF_ONECOMP32F ) )
 	{
 		if( !glConfig.textureFloatAvailable ) {
@@ -1091,31 +1105,59 @@ void R_UploadImage( const char *name, const byte **dataArray, int numLayers, int
 
 		if ( internalFormat == GL_RGB8 )
 		{
-			if ( isSRGB && !glConfig.textureSrgbR8Available )
-			{
-				break;
-			}
-
 			/* Scan the texture for green and blue channels' max values
 			and verify if the green and blue channels are being used or not. */
 
 			c = image->width * image->height;
 			scan = dataArray[0];
 
-			internalFormat = GL_RED;
+			internalFormat = glConfig.textureRGAvailable ? GL_R8 : GL_RED;
+
+			bool hasGreen = false;
+			bool hasBlue = false;
 
 			for ( i = 0; i < c * 4; i += 4 )
 			{
-				if ( scan[ i + 1 ] != 0 )
+				if ( scan[ i + 2 ] != 0 )
 				{
-					internalFormat = GL_RGB8;
+					hasBlue = true;
 					break;
 				}
 
-				if ( scan[ i + 2 ] != 0 )
+				if ( scan[ i + 1 ] != 0 )
+				{
+					hasGreen = true;
+
+					if ( !glConfig.textureRGAvailable )
+					{
+						break;
+					}
+				}
+			}
+
+			if ( hasBlue )
+			{
+				if ( isSRGB && !glConfig.textureSrgbR8Available )
+				{
+					internalFormat = GL_R8;
+				}
+				else
 				{
 					internalFormat = GL_RGB8;
-					break;
+				}
+			}
+			else if ( hasGreen )
+			{
+				if ( glConfig.textureRGAvailable )
+				{
+					if ( isSRGB && !glConfig.textureSrgbRG8Available )
+					{
+						internalFormat = GL_RGB8;
+					}
+					else
+					{
+						internalFormat = GL_RG8;
+					}
 				}
 			}
 		}
@@ -2812,8 +2854,15 @@ void R_CreateBuiltinImages()
 
 	imageParams.bits = IF_NOPICMIP;
 
+	if ( glConfig.textureRGAvailable )
+	{
+		imageParams.bits |= IF_RG;
+	}
+
 	tr.greenImage = R_CreateImage( "_green", ( const byte ** ) &dataPtr, DIMENSION, DIMENSION, 1, imageParams );
 
+	imageParams.bits = IF_NOPICMIP;
+
 	// blue
 	for ( x = DIMENSION * DIMENSION, out = data; x; --x, out += 4 )
 	{

src/engine/renderer/tr_local.h

@@ -485,7 +485,8 @@ enum class ssaoMode {
 	  IF_BC5 = BIT( 23 ),
 	  IF_RGBA32UI = BIT( 24 ),
 	  IF_HOMEPATH = BIT( 25 ),
-	  IF_NOALPHA = BIT( 26 )
+	  IF_NOALPHA = BIT( 26 ),
+	  IF_RG = BIT(27)
 	};
 
 	enum class filterType_t

src/engine/renderer/tr_public.h

@@ -139,6 +139,7 @@ struct GLConfig
 	bool gpuShader5Available;
 	bool textureGatherAvailable;
 	bool textureSrgbR8Available;
+	bool textureSrgbRG8Available;
 	int      maxDrawBuffers;
 
 	float    maxTextureAnisotropy;

src/engine/sys/sdl_glimp.cpp

@@ -106,6 +106,8 @@ static Cvar::Cvar<bool> r_arb_texture_barrier( "r_arb_texture_barrier",
 	"Use GL_ARB_texture_barrier if available", Cvar::NONE, true );
 static Cvar::Cvar<bool> r_arb_texture_gather( "r_arb_texture_gather",
 	"Use GL_ARB_texture_gather if available", Cvar::NONE, true );
+static Cvar::Cvar<bool> r_arb_texture_rg( "r_arb_texture_rg",
+	"Use GL_ARB_texture_rg if available", Cvar::NONE, true );
 static Cvar::Cvar<bool> r_arb_uniform_buffer_object( "r_arb_uniform_buffer_object",
 	"Use GL_ARB_uniform_buffer_object if available", Cvar::NONE, true );
 static Cvar::Cvar<bool> r_arb_vertex_attrib_binding( "r_arb_vertex_attrib_binding",
@@ -124,6 +126,8 @@ static Cvar::Cvar<bool> r_ext_texture_rg( "r_ext_texture_rg",
 	"Use GL_EXT_texture_rg if available", Cvar::NONE, true );
 static Cvar::Cvar<bool> r_ext_texture_srgb_r8( "r_ext_texture_srgb_r8",
 	"Use GL_EXT_texture_sRGB_R8 if available", Cvar::NONE, true );
+static Cvar::Cvar<bool> r_ext_texture_srgb_rg8( "r_ext_texture_srgb_rg8",
+	"Use GL_EXT_texture_sRGB_RG8 if available", Cvar::NONE, true );
 static Cvar::Cvar<bool> r_khr_debug( "r_khr_debug",
 	"Use GL_KHR_debug if available", Cvar::NONE, true );
 static Cvar::Cvar<bool> r_khr_shader_subgroup( "r_khr_shader_subgroup",
@@ -2118,6 +2122,9 @@ static void GLimp_InitExtensions()
 	// made required in OpenGL 3.0
 	glConfig.textureFloatAvailable = LOAD_EXTENSION_WITH_TEST( ExtFlag_CORE, ARB_texture_float, r_ext_texture_float.Get() );
 
+	// made required in OpenGL 3.0
+	glConfig.textureRGAvailable = LOAD_EXTENSION_WITH_TEST( ExtFlag_CORE, ARB_texture_rg, r_ext_texture_rg.Get() );
+
 	bool gpuShader4Enabled = r_ext_gpu_shader4.Get();
 
 	if ( gpuShader4Enabled
@@ -2215,6 +2222,9 @@ static void GLimp_InitExtensions()
 
 	glConfig.textureSrgbR8Available = LOAD_EXTENSION_WITH_TEST( ExtFlag_NONE, EXT_texture_sRGB_R8, r_ext_texture_srgb_r8.Get() );
 
+	// Texture - others
+	glConfig.textureSrgbRG8Available = LOAD_EXTENSION_WITH_TEST( ExtFlag_NONE, EXT_texture_sRGB_RG8, r_ext_texture_srgb_rg8.Get() );
+
 	// Texture - others
 	glConfig.textureAnisotropyAvailable = false;
 	glConfig.textureAnisotropy = 0.0f;