Add RSF_FORCE_LIGHTMAP

Replaces RSF_NOLIGHTSCALE.

If this flag is used when registering a shader, all `ST_COLORMAP` stages will be changed to `ST_DIFFUSEMAP`. This is intended for use with particles and trails, to make them use the lightGrid in the GLSL code.

src/engine/renderer/tr_local.h

@@ -1322,6 +1322,8 @@ enum class shaderProfilerRenderSubGroupsMode {
 
 		int		autoSpriteMode;
 
+		bool forceLightMap;
+
 		uint8_t         numDeforms;
 		deformStage_t   deforms[ MAX_SHADER_DEFORMS ];
 

src/engine/renderer/tr_shader.cpp

@@ -5888,6 +5888,17 @@ static shader_t *FinishShader()
 	numStages = MAX_SHADER_STAGES;
 	GroupActiveStages();
 
+	if ( shader.forceLightMap ) {
+		for( size_t stage = 0; stage < numStages; stage++ ) {
+			shaderStage_t* pStage = &stages[numStages];
+
+			// TODO: Add lightmap as the first stage if there's a heatHaze stage here?
+			if ( pStage->type == stageType_t::ST_COLORMAP ) {
+				pStage->type = stageType_t::ST_DIFFUSEMAP;
+			}
+		}
+	}
+
 	// set appropriate stage information
 	for ( size_t stage = 0; stage < numStages; stage++ )
 	{
@@ -6375,6 +6386,11 @@ shader_t       *R_FindShader( const char *name, shaderType_t type, int flags )
 		shader.entitySpriteFaceViewDirection = true;
 	}
 
+	if ( flags & RSF_FORCE_LIGHTMAP )
+	{
+		shader.forceLightMap = true;
+	}
+
 	// attempt to define shader from an explicit parameter file
 	shaderText = FindShaderInShaderText( strippedName );
 

src/engine/renderer/tr_types.h

@@ -90,7 +90,7 @@ enum RegisterShaderFlags_t {
 	RSF_NOMIP = BIT( 2 ),
 	RSF_FITSCREEN = BIT( 3 ),
 	RSF_LIGHT_ATTENUATION = BIT( 4 ),
-	RSF_NOLIGHTSCALE = BIT( 5 ), // TODO(0.56): delete, does nothing
+	RSF_FORCE_LIGHTMAP = BIT( 5 ), // Used to make particles/trails work with the lightGrid in GLSL
 	RSF_SPRITE = BIT( 6 ),
 };