Sprite directional lighting, add SpriteBacklight option to level header

- Sprites have directional lighting, like walls
- For normal sprites: contrast is much stronger than walls
- Papersprites look the same as walls

- SpriteBacklight option in level header weakens the contrast for sprites only
  - SpriteBacklight subtracts from LightContrast
  - E.g. SpriteBacklight = 0 would let it match LightContrast
  - E.g. SpriteBacklight = 60 would make the contrast much weaker
  - Negative values make the contrast stronger

src/deh_soc.c

@@ -1278,6 +1278,10 @@ void readlevelheader(MYFILE *f, char * name)
 			{
 				mapheaderinfo[num]->light_contrast = (UINT8)i;
 			}
+			else if (fastcmp(word, "SPRITEBACKLIGHT"))
+			{
+				mapheaderinfo[num]->sprite_backlight = (SINT8)i;
+			}
 			else if (fastcmp(word, "LIGHTANGLE"))
 			{
 				if (fastcmp(word2, "EVEN"))

src/doomstat.h

@@ -503,6 +503,7 @@ struct mapheader_t
 	UINT16 palette;						///< PAL lump to use on this map
 	UINT16 encorepal;					///< PAL for encore mode
 	UINT8 light_contrast;				///< Range of wall lighting. 0 is no lighting.
+	SINT8 sprite_backlight;				///< Subtract from wall lighting for sprites only.
 	boolean use_light_angle;			///< When false, wall lighting is evenly distributed. When true, wall lighting is directional.
 	angle_t light_angle;				///< Angle of directional wall lighting.
 
@@ -762,6 +763,7 @@ extern fixed_t mapobjectscale;
 extern struct maplighting
 {
 	UINT8 contrast;
+	SINT8 backlight;
 	boolean directional;
 	angle_t angle;
 } maplighting;

src/p_setup.c

@@ -438,6 +438,7 @@ static void P_ClearSingleMapHeaderInfo(INT16 num)
 	mapheaderinfo[num]->mobj_scale = FRACUNIT;
 	mapheaderinfo[num]->default_waypoint_radius = 0;
 	mapheaderinfo[num]->light_contrast = 16;
+	mapheaderinfo[num]->sprite_backlight = 0;
 	mapheaderinfo[num]->use_light_angle = false;
 	mapheaderinfo[num]->light_angle = 0;
 #if 1 // equivalent to "Followers = DEFAULT"

src/p_spec.c

@@ -6732,6 +6732,7 @@ void P_InitSpecials(void)
 
 	// Set map lighting settings.
 	maplighting.contrast = mapheaderinfo[gamemap-1]->light_contrast;
+	maplighting.backlight = mapheaderinfo[gamemap-1]->sprite_backlight;
 	maplighting.directional = mapheaderinfo[gamemap-1]->use_light_angle;
 	maplighting.angle = mapheaderinfo[gamemap-1]->light_angle;
 

src/r_things.c

@@ -1630,6 +1630,26 @@ static void R_ProjectBoundingBox(mobj_t *thing, vissprite_t *vis)
 	box->x2test = 0;
 }
 
+static fixed_t R_GetSpriteDirectionalLighting(angle_t angle)
+{
+	// Copied from P_UpdateSegLightOffset
+	const UINT8 contrast = min(max(0, maplighting.contrast - maplighting.backlight), UINT8_MAX);
+	const fixed_t contrastFixed = ((fixed_t)contrast) * FRACUNIT;
+
+	fixed_t light = FRACUNIT;
+	fixed_t extralight = 0;
+
+	light = FixedMul(FINECOSINE(angle >> ANGLETOFINESHIFT), FINECOSINE(maplighting.angle >> ANGLETOFINESHIFT))
+		+ FixedMul(FINESINE(angle >> ANGLETOFINESHIFT), FINESINE(maplighting.angle >> ANGLETOFINESHIFT));
+	light = (light + FRACUNIT) / 2;
+
+	light = FixedMul(light, FRACUNIT - FSIN(abs(AngleDeltaSigned(angle, maplighting.angle)) / 2));
+
+	extralight = -contrastFixed + FixedMul(light, contrastFixed * 2);
+
+	return extralight;
+}
+
 //
 // R_ProjectSprite
 // Generates a vissprite for a thing
@@ -2275,6 +2295,38 @@ static void R_ProjectSprite(mobj_t *thing)
 
 		lightnum = (lightnum + R_ThingLightLevel(oldthing)) >> LIGHTSEGSHIFT;
 
+		if (maplighting.directional == true)
+		{
+			fixed_t extralight = R_GetSpriteDirectionalLighting(papersprite
+					? interp.angle + (ang >= ANGLE_180 ? -ANGLE_90 : ANGLE_90)
+					: R_PointToAngle(interp.x, interp.y));
+
+			// Less change in contrast in dark sectors
+			extralight = FixedMul(extralight, min(max(0, lightnum), LIGHTLEVELS - 1) * FRACUNIT / (LIGHTLEVELS - 1));
+
+			if (papersprite)
+			{
+				// Papersprite contrast should match walls
+				lightnum += FixedFloor((extralight / 8) + (FRACUNIT / 2)) / FRACUNIT;
+			}
+			else
+			{
+				fixed_t n = FixedDiv(FixedMul(xscale, LIGHTRESOLUTIONFIX), ((MAXLIGHTSCALE-1) << LIGHTSCALESHIFT));
+
+				// Less change in contrast at further distances, to counteract DOOM diminished light
+				extralight = FixedMul(extralight, min(n, FRACUNIT));
+
+				// Contrast is stronger for normal sprites, stronger than wall lighting is at the same distance
+				lightnum += FixedFloor((extralight / 4) + (FRACUNIT / 2)) / FRACUNIT;
+			}
+
+			// Semibright objects will be made slightly brighter to compensate contrast
+			if (R_ThingIsSemiBright(oldthing))
+			{
+				lightnum += 2;
+			}
+		}
+
 		if (lightnum < 0)
 			lights_array = scalelight[0];
 		else if (lightnum >= LIGHTLEVELS)