light: implement the -gate option

Precalculate the distance at which lights will fade to zero brightness.
For lights with inverse falloff, use the gate value to determine the
cut-off distance.  Use this value to cull samples and avoid the ray
tracing overhead.

Hopefully not too controversially, I am going to default this to "on" with
a gate value of 0.001. Unless you have > 1000 lights contributing
fractional light values across your map, this is not going to make any
visible difference.

Signed-off-by: Kevin Shanahan <kmshanah@disenchant.net>

changelog.txt

@@ -8,6 +8,7 @@
 * light: removed old bsp30 support
 * light: lit files now automatically generated when coloured lights detected
 * light: implemented 4x4 oversampling with -extra4 command line
+* light: implemented the -gate option to help speed processing (default 0.001)
 
 2013-02-25 TyrUtils v0.5
 

include/common/mathlib.h

@@ -20,12 +20,15 @@
 #ifndef __COMMON_MATHLIB_H__
 #define __COMMON_MATHLIB_H__
 
+#include <float.h>
 #include <math.h>
 
 #ifdef DOUBLEVEC_T
 typedef double vec_t;
+#define VECT_MAX DBL_MAX;
 #else
 typedef float vec_t;
+#define VECT_MAX FLT_MAX;
 #endif
 typedef vec_t vec3_t[3];
 

include/light/entities.h

@@ -62,6 +62,7 @@ typedef struct entity_s {
     float atten;
     light_formula_t formula;
     vec3_t lightcolor;
+    vec_t fadedist;
 
     char target[MAX_ENT_VALUE];
     char targetname[MAX_ENT_VALUE];

include/light/light.h

@@ -45,6 +45,7 @@ void MakeTnodes(void);
 
 extern float scaledist;
 extern float rangescale;
+extern float fadegate;
 extern int worldminlight;
 extern const vec3_t vec3_white;
 extern vec3_t minlight_color;

light.txt

@@ -37,6 +37,13 @@ OPTIONS
 	               The same effect can be achieved on individual lights by
 	               adjusting both the "light" and "wait" attributes.
 
+	-gate n        Set a minimum light level, below which can be considered
+	               zero brightness.  This can dramatically speed up
+	               processing when there are large numbers of lights with
+	               inverse or inverse square falloff. In most cases, values
+	               less than 1.0 will cause no discernable visual
+	               differences.  Default 0.001.
+
 	-colored       (DEPRECATED) Turn on coloured lighting support. By
 	-coloured      default this will output a bsp in "BSP30" format, which
 	               almost no Quake engines support. BSP30 support will be

light/entities.c

@@ -186,6 +186,40 @@ CheckEntityFields(entity_t *entity)
     } else {
 	VectorCopy(vec3_white, entity->lightcolor);
     }
+
+    if (entity->formula == LF_LINEAR) {
+	/* Linear formula always has a falloff point */
+	entity->fadedist = fabs(entity->light / entity->atten / scaledist);
+    } else if (fadegate < EQUAL_EPSILON) {
+	/* If fadegate is tiny, other lights have effectively infinite reach */
+	entity->fadedist = VECT_MAX;
+    } else {
+	/* Calculate the distance at which brightness falls to zero */
+	switch (entity->formula) {
+	case LF_INFINITE:
+	case LF_LOCALMIN:
+	    entity->fadedist = VECT_MAX;
+	    break;
+	case LF_INVERSE:
+	    entity->fadedist = entity->light * entity->atten * scaledist;
+	    entity->fadedist *= LF_SCALE / fadegate;
+	    entity->fadedist = fabs(entity->fadedist);
+	    break;
+	case LF_INVERSE2:
+	    entity->fadedist = entity->light * entity->atten * scaledist;
+	    entity->fadedist *= LF_SCALE / sqrt(fadegate);
+	    entity->fadedist = fabs(entity->fadedist);
+	    break;
+	case LF_INVERSE2A:
+	    entity->fadedist = entity->light * entity->atten * scaledist;
+	    entity->fadedist -= LF_SCALE;
+	    entity->fadedist *= LF_SCALE / sqrt(fadegate);
+	    entity->fadedist = fabs(entity->fadedist);
+	    break;
+	default:
+	    Error("Internal error: formula not handled in %s", __func__);
+	}
+    }
 }
 
 

light/light.c

@@ -23,6 +23,7 @@
 
 float scaledist = 1.0;
 float rangescale = 0.5;
+float fadegate = EQUAL_EPSILON;
 int worldminlight = 0;
 int sunlight = 0;
 const vec3_t vec3_white = { 255, 255, 255 };
@@ -209,6 +210,9 @@ main(int argc, const char **argv)
 	} else if (!strcmp(argv[i], "-range")) {
 	    rangescale = atof(argv[i + 1]);
 	    i++;
+	} else if (!strcmp(argv[i], "-gate")) {
+	    fadegate = atof(argv[i + 1]);
+	    i++;
 	} else if (!strcmp(argv[i], "-light")) {
 	    worldminlight = atof(argv[i + 1]);
 	    i++;
@@ -232,7 +236,7 @@ main(int argc, const char **argv)
 
     if (i != argc - 1)
 	Error("usage: light [-threads num] [-light num] [-extra|-extra4]\n"
-	      "             [-dist n] [-range n] [-lit] [-compress]\n"
+	      "             [-dist n] [-range n] [-gate n] [-lit] [-compress]\n"
 	      "             [-nominlimit] bspfile\n");
 
     start = I_FloatTime();

light/ltface.c

@@ -556,6 +556,12 @@ SingleLightFace(const entity_t *light, lightinfo_t * l,
 
 	VectorSubtract(light->origin, surf, ray);
 	dist = VectorLength(ray);
+
+	/* Quick distance check first */
+	if (dist > light->fadedist)
+	    continue;
+
+	/* Check spotlight cone */
 	VectorScale(ray, 1.0 / dist, ray);
 	angle = DotProduct(ray, l->facenormal);
 	if (light->spotlight) {