-multiSun commandline flag: Draw sun/skylights only if they come from the sky whose shader they were defined in.

Every shader that emits sun or skyligghts gets an environment emitter index. All the suns/lights generated from that shader get the same index.
trace_t now has a bitmask of all the environment emitter indices encountered when hitting sky surfaces and checking their shader.
Lighting code checks whether the current sunlight has a defined environment emitter index and if it does, it checks whether it is set in the bitmask. Only then will the light be considered to hit.

docs/Complete_list_of_command_line_parameters.htm

@@ -260,6 +260,7 @@ td.formatted_questions ol { margin-top: 0px; margin-bottom: 0px; }
 		<li><strong><code>-lomem</code>:</strong> Low memory but slower lighting mode</li>
 		<li><strong><code>-lowquality</code>:</strong> Low quality floodlight (appears to currently break floodlight)</li>
 		<li><strong><code>-minsamplesize</code> N:</strong> Sets minimum lightmap resolution in luxels/qu</li>
+		<li><strong><code>-multiSun</code> N:</strong> Restrict sun and skylights to being emitted from surfaces carrying the shader they were defined in (as opposed to globally)</li>
 		<li><strong><code>-nobouncestore</code>:</strong> Do not store BSP, lightmap and shader files between bounces</li>
 		<li><strong><code>-nocollapse</code>:</strong> Do not collapse identical lightmaps</li>
 		<li><strong><code>-nodeluxe</code>, <code>-nodeluxemap</code>:</strong> Disable deluxemapping</li>

docs/shaderManual/q3map-global-directives.html

@@ -401,6 +401,11 @@ textures/eerie/ironcrosslt2_10000
 	<dt>sample_color</dt><dd>Default = 1: sample color of each individual light from skybox images, if they are present. 0: use shader color, set by <a href="q3map-global-directives.html#q3map_lightRGB">q3map_lightRGB</a>/<a href="q3map-global-directives.html#q3map_lightImage">q3map_lightImage</a>/<a href="general-directives.html#skyParms">_up skybox image</a>/<a href="quake-editor-radiant-directives.html#qer_editorImage">qer_editorImage</a>.</dd>
 </dl>
 
+<blockquote>
+	<h4>Design Notes:</h4>
+	<p>Normally, all suns and skylights are emitted from all sky surfaces in a map. If you wish to restrict them to being emitted from surfaces carrying the exact shader that defined them, e.g. to have different sun/sky lighting in different areas of the map, compile your map with the -multiSun keyword in the light stage.</p>
+</blockquote>
+
 <h2 id="q3map_splotchFix">q3map_splotchFix</h2>
 <p>This is used on lightmapped model shaders if splotched lighting artifacts appear. Any shadows at the ambient/dark level will be flooded from neighbouring luxels. This gets rid of shadow acne, but a surface must be more or less uniformly lit or this looks ugly. Try using <a href="q3map-global-directives.html#q3map_lightmapSampleOffset">q3map_lightmapSampleOffset</a> first before using this as a last resort.</p>
 
@@ -428,6 +433,8 @@ textures/eerie/ironcrosslt2_10000
 	<p>Sky shaders should probably still have a <a href="q3map-global-directives.html#q3map_surfaceLight">q3map_surfaceLight</a> or preferred <a href="q3map-global-directives.html#q3map_skylight">q3map_skylight</a> value. The "sun" gives a strong directional light, but doesn't necessarily give the fill light needed to soften and illuminate shadows. Skies with clouds should probably have a weaker <a href="q3map-global-directives.html#q3map_sun">q3map_sun</a> value and a higher <a href="q3map-global-directives.html#q3map_surfaceLight">q3map_surfaceLight</a> or <a href="q3map-global-directives.html#q3map_skylight">q3map_skylight</a> value. Heavy clouds diffuse light and weaken shadows. The opposite is true of a cloudless or nearly cloudless sky. In such cases, the "sun" or "moon" will cast stronger shadows that have a greater degree of contrast. This is also why q3map_sunExt is preferred. It gives the designer greater control over shadow contrast with a penumbra effect.</p>
 	<h4>Design Notes:</h4>
 	<p>Not certain what color formula you want to use for the sun's light? Try this. Create a light entity. Use the Radiant editor's color selection tools to pick a color. The light's _color key's value will be the normalized RGB formula. Copy it from the value line in the editor (CTRL+c) and paste it into your shader.</p>
+	<h4>Design Notes:</h4>
+	<p>Normally, all suns and skylights are emitted from all sky surfaces in a map. If you wish to restrict them to being emitted from surfaces carrying the exact shader that defined them, e.g. to have different sun/sky lighting in different areas of the map, compile your map with the -multiSun keyword in the light stage.</p>
 </blockquote>
 
 <h2 id="q3map_surfaceLight">q3map_surfaceLight value</h2>

tools/quake3/q3map2/help.cpp

@@ -226,6 +226,7 @@ static void HelpLight()
 		{ "-lomem", "Low memory but slower lighting mode" },
 		{ "-lowquality", "Low quality floodlight (appears to currently break floodlight)" },
 		{ "-minsamplesize <N>", "Sets minimum lightmap resolution in luxels/qu" },
+		{ "-multisun", "Restrict sun and skylights to being emitted from surfaces carrying the shader they were defined in (as opposed to globally)" },
 		{ "-nobouncestore", "Do not store BSP, lightmap and shader files between bounces" },
 		{ "-nocollapse", "Do not collapse identical lightmaps" },
 		{ "-nodeluxe, -nodeluxemap", "Disable deluxemapping" },

tools/quake3/q3map2/light.cpp

@@ -100,6 +100,7 @@ static void CreateSunLight( sun_t& sun ){
 		light.falloffTolerance = falloffTolerance;
 		light.filterRadius = sun.filterRadius / sun.numSamples;
 		light.style = noStyles ? LS_NORMAL : sun.style;
+		light.environmentLightIndex = sun.environmentLightIndex;
 
 		/* set the light's position out to infinity */
 		light.origin = direction * ( MAX_WORLD_COORD * 8.0f );    /* MAX_WORLD_COORD * 2.0f */
@@ -234,6 +235,7 @@ static void CreateSkyLights( const skylight_t& skylight, const Vector3& color, f
 	sun.deviance = 0.0f;
 	sun.filterRadius = filterRadius;
 	sun.numSamples = 1;
+	sun.environmentLightIndex = skylight.environmentLightIndex;
 	sun.style = noStyles ? LS_NORMAL : style;
 
 	/* setup */
@@ -599,6 +601,16 @@ static void CreateSurfaceLights(){
 		if ( !si->suns.empty() && !nss ) {
 			auto* si_ = const_cast<shaderInfo_t*>( si );   /* FIXME: hack! */
 			Sys_FPrintf( SYS_VRB, "Sun: %s\n", si->shader.c_str() );
+			if(multiSun){
+				if(si->environmentEmitterIndex == -1){
+					// this shader is actually emitting sun/skylight now, so give it an environment emitter index
+					si_->environmentEmitterIndex = nextEnvironmentLightIndex++;
+				}
+				// let the suns know
+				for( auto sunIt = si_->suns.begin(); sunIt != si_->suns.end(); sunIt++ ){
+					sunIt->environmentLightIndex = si_->environmentEmitterIndex;
+				}
+			}
 			std::ranges::for_each( si_->suns, CreateSunLight );
 			si_->suns.clear();   /* FIXME: hack! */
 		}
@@ -606,6 +618,17 @@ static void CreateSurfaceLights(){
 		/* sky light? */
 		if ( !si->skylights.empty() ) {
 			Sys_FPrintf( SYS_VRB, "Sky: %s\n", si->shader.c_str() );
+			if(multiSun){
+				shaderInfo_t* si_ = const_cast<shaderInfo_t*>( si );   /* FIXME: hack! */
+				if(si->environmentEmitterIndex == -1){
+					// this shader is actually emitting sun/skylight now, so give it an environment emitter index
+					si_->environmentEmitterIndex = nextEnvironmentLightIndex++;
+				}
+				// let the skies know
+				for( auto skyIt = si_->skylights.begin(); skyIt != si_->skylights.end(); skyIt++ ){
+					skyIt->environmentLightIndex = si_->environmentEmitterIndex;
+				}
+			}
 			for( const skylight_t& skylight : si->skylights )
 				CreateSkyLights( skylight, si->color, si->lightFilterRadius, si->lightStyle, si->skyParmsImageBase );
 			const_cast<shaderInfo_t*>( si )->skylights.clear();   /* FIXME: hack! */
@@ -1098,7 +1121,7 @@ int LightContributionToSample( trace_t *trace ){
 			/* trace */
 			TraceLine( trace );
 			trace->forceSubsampling *= add;
-			if ( !( trace->compileFlags & C_SKY ) || trace->opaque ) {
+			if ( !( trace->compileFlags & C_SKY ) || trace->opaque || multiSun && light->environmentLightIndex != -1 && light->environmentLightIndex < MULTISUN_MAX && !bit_is_enabled(trace->skyEnvironmentLightIndices,light->environmentLightIndex) ) {
 				trace->color.set( 0 );
 				trace->directionContribution.set( 0 );
 
@@ -1394,7 +1417,7 @@ static bool LightContributionToPoint( trace_t *trace ){
 		if ( trace->testOcclusion && !trace->forceSunlight ) {
 			/* trace */
 			TraceLine( trace );
-			if ( !( trace->compileFlags & C_SKY ) || trace->opaque ) {
+			if ( !( trace->compileFlags & C_SKY ) || trace->opaque || multiSun && light->environmentLightIndex != -1 && light->environmentLightIndex < MULTISUN_MAX && !bit_is_enabled(trace->skyEnvironmentLightIndices,light->environmentLightIndex) ) {
 				trace->color.set( 0 );
 				return false;
 			}
@@ -2496,6 +2519,10 @@ int LightMain( Args& args ){
 				Sys_Printf( "Approximating lightmaps within a byte tolerance of %d\n", approximateTolerance );
 			}
 		}
+		while ( args.takeArg( "-multisun" ) ) {
+			multiSun = true;
+			Sys_Printf( "Multi-sun support activated\n" );
+		}
 		while ( args.takeArg( "-deluxe", "-deluxemap" ) ) {
 			deluxemap = true;
 			Sys_Printf( "Generating deluxemaps for average light direction\n" );

tools/quake3/q3map2/light_trace.cpp

@@ -1351,6 +1351,9 @@ static bool TraceTriangle( traceInfo_t *ti, traceTriangle_t *tt, trace_t *trace
 
 	/* don't trace against sky */
 	if ( si->compileFlags & C_SKY ) {
+		if(multiSun && trace->light && trace->light->environmentLightIndex != -1 && si->environmentEmitterIndex != -1 && si->environmentEmitterIndex < MULTISUN_MAX){
+			bit_enable(trace->skyEnvironmentLightIndices,si->environmentEmitterIndex);
+		}
 		return false;
 	}
 
@@ -1597,6 +1600,9 @@ void TraceLine( trace_t *trace ){
 	trace->passSolid = false;
 	trace->opaque = false;
 	trace->compileFlags = 0;
+	if(multiSun){
+		memset(trace->skyEnvironmentLightIndices,0,sizeof(trace->skyEnvironmentLightIndices));
+	}
 	trace->numTestNodes = 0;
 
 	/* early outs */

tools/quake3/q3map2/q3map2.h

@@ -155,6 +155,9 @@ enum class EBrushType
 
 
 /* light */
+#define MULTISUN_MAX			2048 // TA: multi sun. this is how many separate suns can be drawn separately and only where they should
+#define MULTISUN_MAX_BYTES		(MULTISUN_MAX/8) // it's a bitmask. 256 bytes in the end.
+
 #define MAX_TRACE_TEST_NODES    256
 #define DEFAULT_INHIBIT_RADIUS  1.5f
 
@@ -414,6 +417,7 @@ struct sun_t
 	Vector3 direction, color;
 	float photons, deviance, filterRadius;
 	int numSamples, style;
+	int environmentLightIndex = -1;
 };
 
 struct skylight_t
@@ -423,6 +427,7 @@ struct skylight_t
 	int horizon_min = 0;
 	int horizon_max = 90;
 	bool sample_color = true;
+	int environmentLightIndex = -1;
 };
 
 
@@ -579,6 +584,7 @@ struct shaderInfo_t_data
 
 	std::vector<skylight_t>  skylights;                 /* ydnar */
 	std::vector<sun_t>  suns;                           /* ydnar */
+	int	environmentEmitterIndex = -1;           		/* TA: multisun: shaders that end up being used and actually emit sunlight get a unique emitter index */
 
 	Vector3 color{ 0 };                                 /* normalized color */
 	Color4f averageColor = { 0, 0, 0, 0 };
@@ -1083,6 +1089,8 @@ struct light_t
 
 	float falloffTolerance;             /* ydnar: minimum attenuation threshold */
 	float filterRadius;                 /* ydnar: lightmap filter radius in world units, 0 == default */
+
+	int environmentLightIndex = -1;		/* TA: For sun/skylights. Check if particular sky triangle emits a given light  */
 };
 
 
@@ -1106,9 +1114,12 @@ struct trace_t
 	float inhibitRadius;                /* sphere in which occluding geometry is ignored */
 
 	/* per-light input */
-	const light_t             *light;
+	const light_t             *light = nullptr;
 	Vector3 end;
 
+	/* TA: multisun support */
+	byte	skyEnvironmentLightIndices[MULTISUN_MAX_BYTES];
+
 	/* calculated input */
 	Vector3 displacement, direction;
 	float distance;
@@ -2026,6 +2037,10 @@ inline const bool exactPointToPolygon = true;
 inline const float formFactorValueScale = 3.0f;
 inline const float linearScale = 1.0f / 8000.0f;
 
+/* TA: multisun stuff (ability to have mutliple skyboxes with separate suns/skylights). May not handle _skybox properly */
+inline bool multiSun = false;
+inline int nextEnvironmentLightIndex = 0; // each shader environment light (sun/sky) gets a unique index. thus we can check whether a sky surface should be considered as a successful trace
+
 inline std::list<light_t> lights;
 inline int numPointLights;
 inline int numSpotLights;