renderer: implement dithering

Author: illwieckz

src/engine/renderer/gl_shader.cpp

@@ -799,6 +799,10 @@ static std::string GenEngineConstants() {
 		AddDefine( str, "r_highPrecisionRendering", 1 );
 	}
 
+	if ( r_dithering.Get() ) {
+		AddDefine( str, "r_dithering", 1 );
+	}
+
 	return str;
 }
 
@@ -3066,4 +3070,4 @@ GlobalUBOProxy::GlobalUBOProxy() :
 	u_Tonemap( this ),
 	u_TonemapParms( this ),
 	u_Exposure( this ) {
-}
+}

src/engine/renderer/glsl_source/cameraEffects_fp.glsl

@@ -92,6 +92,22 @@ void main()
 	}
 #endif
 
+#if defined(r_dithering)
+	const float bayer[ 16 ] = {
+		 0.0f,  8.0f,  2.0f, 10.0f,
+		12.0f,  4.0f, 14.0f,  6.0f,
+		 3.0f, 11.0f,  1.0f,  9.0f,
+		15.0f,  7.0f, 13.0f,  5.0f
+	};
+
+	float dither = bayer[
+			int( mod( gl_FragCoord.x, 4.0 ) ) +
+			int( mod( gl_FragCoord.y, 4.0 ) ) * 4
+		] / 16.0;
+
+	color.rgb += vec3( ( dither - 0.50 ) / 255.0 );
+#endif
+
 	color.rgb = clamp( color.rgb, vec3( 0.0f ), vec3( 1.0f ) );
 
 	if ( u_SRGB )

src/engine/renderer/tr_init.cpp

@@ -206,6 +206,9 @@ Cvar::Cvar<int> r_rendererAPI( "r_rendererAPI", "Renderer API: 0: OpenGL, 1: Vul
 		"r_toneMappingDarkAreaPointLDR", "Convert to this brightness at dark area cut-off",
 		Cvar::NONE, 0.268f, 0.0f, 1.0f );
 
+	Cvar::Cvar<bool> r_dithering(
+		"r_dithering", "Use dithering", Cvar::NONE, true );
+
 	cvar_t      *r_lockpvs;
 	cvar_t      *r_noportals;
 
@@ -1267,6 +1270,7 @@ ScreenshotCmd screenshotPNGRegistration("screenshotPNG", ssFormat_t::SSF_PNG, "p
 
 		Cvar::Latch( r_highPrecisionRendering );
 		Cvar::Latch( r_accurateSRGB );
+		Cvar::Latch( r_dithering );
 
 		r_drawBuffer = Cvar_Get( "r_drawBuffer", "GL_BACK", CVAR_CHEAT );
 		r_lockpvs = Cvar_Get( "r_lockpvs", "0", CVAR_CHEAT );

src/engine/renderer/tr_local.h

@@ -2716,6 +2716,7 @@ enum
 
 	extern Cvar::Cvar<bool> r_highPrecisionRendering;
 	extern Cvar::Cvar<bool> r_accurateSRGB;
+	extern Cvar::Cvar<bool> r_dithering;
 
 	extern Cvar::Range<Cvar::Cvar<int>> r_shadows;