Eevee: Add Light Threshold value

This is an important change. Starting from now, all lights have a finite
influence radius (similar to the old sphere option for BI).

In order to avoid costly setup time, this distance is first computed
automatically based on a light threshold. The distance is computed
at the light origin and using the inverse square falloff. The setting
can be found inside the render settings panel > shadow tab.

This light threshold does not take the light shape into account an may not
suit every case. That's why we provide a per lamp override where you can
just set the cutt off distance (Light Properties Panel > Light >
Custom Distance).

The influence distance is also used as shadow far clip distance.

This influence distance does not concerns sun lights that still have a
far clip distance.

---

This change is important because it makes it possible to cull lights
an improve performance drastically in the future.

11 files changed, 136 insertions, 46 deletions

diff --git a/source/blender/blenkernel/intern/lamp.c b/source/blender/blenkernel/intern/lamp.c
index a2571c8cee5..8768810ccff 100644
--- a/source/blender/blenkernel/intern/lamp.c
+++ b/source/blender/blenkernel/intern/lamp.c
@@ -89,6 +89,7 @@ void BKE_lamp_init(Lamp *la)
 	la->contact_spread = 0.2f;
 	la->contact_thickness = 0.2f;
 	la->spec_fac = 1.0f;
+	la->att_dist = 40.0f;
 
 	curvemapping_initialize(la->curfalloff);
 }
diff --git a/source/blender/blenkernel/intern/scene.c b/source/blender/blenkernel/intern/scene.c
index af27103b07e..ee30179e632 100644
--- a/source/blender/blenkernel/intern/scene.c
+++ b/source/blender/blenkernel/intern/scene.c
@@ -915,6 +915,7 @@ void BKE_scene_init(Scene *sce)
 	sce->eevee.shadow_cascade_size = 1024;
 
 	sce->eevee.light_cache = NULL;
+	sce->eevee.light_threshold = 0.01f;
 
 	sce->eevee.overscan = 3.0f;
 
diff --git a/source/blender/blenloader/intern/versioning_280.c b/source/blender/blenloader/intern/versioning_280.c
index 9521c05f7f0..1871aea86a4 100644
--- a/source/blender/blenloader/intern/versioning_280.c
+++ b/source/blender/blenloader/intern/versioning_280.c
@@ -2265,6 +2265,18 @@ void blo_do_versions_280(FileData *fd, Library *UNUSED(lib), Main *bmain)
 			}
 		}
 
+		if (!DNA_struct_elem_find(fd->filesdna, "SceneEEVEE", "float", "light_threshold")) {
+			for (Scene *scene = bmain->scene.first; scene; scene = scene->id.next) {
+				scene->eevee.light_threshold = 0.01f;
+			}
+		}
+
+		if (!DNA_struct_elem_find(fd->filesdna, "Lamp", "float", "att_dist")) {
+			for (Lamp *la = bmain->lamp.first; la; la = la->id.next) {
+				la->att_dist = la->clipend;
+			}
+		}
+
 		if (!DNA_struct_elem_find(fd->filesdna, "Brush", "char", "weightpaint_tool")) {
 			/* Magic defines from old files (2.7x) */
 
diff --git a/source/blender/draw/engines/eevee/eevee_lights.c b/source/blender/draw/engines/eevee/eevee_lights.c
index 5336e197d02..b946a49ea14 100644
--- a/source/blender/draw/engines/eevee/eevee_lights.c
+++ b/source/blender/draw/engines/eevee/eevee_lights.c
@@ -57,8 +57,9 @@ extern char datatoc_shadow_store_frag_glsl[];
 extern char datatoc_shadow_copy_frag_glsl[];
 extern char datatoc_concentric_samples_lib_glsl[];
 
-/* Prototype */
+/* Prototypes */
 static void eevee_light_setup(Object *ob, EEVEE_Light *evli);
+static float light_attenuation_radius_get(Lamp *la, float light_threshold);
 
 /* *********** LIGHT BITS *********** */
 static void lightbits_set_single(EEVEE_LightBits *bitf, uint idx, bool val)
@@ -337,6 +338,9 @@ void EEVEE_lights_cache_add(EEVEE_ViewLayerData *sldata, Object *ob)
 {
 	EEVEE_LampsInfo *linfo = sldata->lamps;
 
+	const DRWContextState *draw_ctx = DRW_context_state_get();
+	const float threshold = draw_ctx->scene->eevee.light_threshold;
+
 	/* Step 1 find all lamps in the scene and setup them */
 	if (linfo->num_light >= MAX_LIGHT) {
 		printf("Too many lights in the scene !!!\n");
@@ -399,7 +403,7 @@ void EEVEE_lights_cache_add(EEVEE_ViewLayerData *sldata, Object *ob)
 					/* Saving lamp bounds for later. */
 					BLI_assert(linfo->cpu_cube_len >= 0 && linfo->cpu_cube_len < MAX_LIGHT);
 					copy_v3_v3(linfo->shadow_bounds[linfo->cpu_cube_len].center, ob->obmat[3]);
-					linfo->shadow_bounds[linfo->cpu_cube_len].radius = la->clipend;
+					linfo->shadow_bounds[linfo->cpu_cube_len].radius = light_attenuation_radius_get(la, threshold);
 
 					EEVEE_ShadowCubeData *data = &led->data.scd;
 					/* Store indices. */
@@ -590,37 +594,25 @@ void EEVEE_lights_cache_finish(EEVEE_ViewLayerData *sldata, EEVEE_Data *vedata)
 	EEVEE_lights_update(sldata, vedata);
 }
 
-/* Update buffer with lamp data */
-static void eevee_light_setup(Object *ob, EEVEE_Light *evli)
+float light_attenuation_radius_get(Lamp *la, float light_threshold)
 {
-	Lamp *la = (Lamp *)ob->data;
-	float mat[4][4], scale[3], power;
-
-	/* Position */
-	copy_v3_v3(evli->position, ob->obmat[3]);
-
-	/* Color */
-	copy_v3_v3(evli->color, &la->r);
-
-	evli->spec = la->spec_fac;
-
-	/* Influence Radius */
-	evli->dist = la->dist;
-
-	/* Vectors */
-	normalize_m4_m4_ex(mat, ob->obmat, scale);
-	copy_v3_v3(evli->forwardvec, mat[2]);
-	normalize_v3(evli->forwardvec);
-	negate_v3(evli->forwardvec);
-
-	copy_v3_v3(evli->rightvec, mat[0]);
-	normalize_v3(evli->rightvec);
-
-	copy_v3_v3(evli->upvec, mat[1]);
-	normalize_v3(evli->upvec);
+	if (la->mode & LA_CUSTOM_ATTENUATION)
+		return la->att_dist;
+
+	/* Compute max light power. */
+	float power = max_fff(la->r, la->g, la->b);
+	power *= fabsf(la->energy);
+	power *= max_ff(1.0f, la->spec_fac);
+	/* Compute the distance (using the inverse square law)
+	 * at which the light power reaches the light_threshold. */
+	float distance = sqrtf(max_ff(1e-16, power / max_ff(1e-16, light_threshold)));
+	return distance;
+}
 
-	/* Spot size & blend */
+static void light_shape_parameters_set(EEVEE_Light *evli, const Lamp *la, float scale[3])
+{
 	if (la->type == LA_SPOT) {
+		/* Spot size & blend */
 		evli->sizex = scale[0] / scale[2];
 		evli->sizey = scale[1] / scale[2];
 		evli->spotsize = cosf(la->spotsize * 0.5f);
@@ -639,16 +631,16 @@ static void eevee_light_setup(Object *ob, EEVEE_Light *evli)
 	else {
 		evli->radius = max_ff(0.001f, la->area_size);
 	}
+}
 
-	/* Lamp Type */
-	evli->lamptype = (float)la->type;
-
+static float light_shape_power_get(const Lamp *la, const EEVEE_Light *evli)
+{
+	float power;
 	/* Make illumination power constant */
 	if (la->type == LA_AREA) {
 		power = 1.0f / (evli->sizex * evli->sizey * 4.0f * M_PI) * /* 1/(w*h*Pi) */
 		        80.0f; /* XXX : Empirical, Fit cycles power */
 		if (ELEM(la->area_shape, LA_AREA_DISK, LA_AREA_ELLIPSE)) {
-			evli->lamptype = LAMPTYPE_AREA_ELLIPSE;
 			/* Scale power to account for the lower area of the ellipse compared to the surrounding rectangle. */
 			power *= 4.0f / M_PI;
 		}
@@ -664,8 +656,54 @@ static void eevee_light_setup(Object *ob, EEVEE_Light *evli)
 		power = 1.0f / (evli->radius * evli->radius * M_PI); /* 1/(r²*Pi) */
 		/* Make illumation power closer to cycles for bigger radii. Cycles uses a cos^3 term that we cannot reproduce
 		 * so we account for that by scaling the light power. This function is the result of a rough manual fitting. */
-		power *= 1.0f + evli->radius * evli->radius * 0.5f;
+		power += 1.0f / (2.0f * M_PI); /* power *= 1 + r²/2 */
+	}
+	return power;
+}
+
+/* Update buffer with lamp data */
+static void eevee_light_setup(Object *ob, EEVEE_Light *evli)
+{
+	Lamp *la = (Lamp *)ob->data;
+	float mat[4][4], scale[3], power, att_radius;
+
+	const DRWContextState *draw_ctx = DRW_context_state_get();
+	const float light_threshold = draw_ctx->scene->eevee.light_threshold;
+
+	/* Position */
+	copy_v3_v3(evli->position, ob->obmat[3]);
+
+	/* Color */
+	copy_v3_v3(evli->color, &la->r);
+
+	evli->spec = la->spec_fac;
+
+	/* Influence Radius */
+	att_radius = light_attenuation_radius_get(la, light_threshold);
+	/* Take the inverse square of this distance. */
+	evli->invsqrdist = 1.0 / max_ff(1e-4f, att_radius * att_radius);
+
+	/* Vectors */
+	normalize_m4_m4_ex(mat, ob->obmat, scale);
+	copy_v3_v3(evli->forwardvec, mat[2]);
+	normalize_v3(evli->forwardvec);
+	negate_v3(evli->forwardvec);
+
+	copy_v3_v3(evli->rightvec, mat[0]);
+	normalize_v3(evli->rightvec);
+
+	copy_v3_v3(evli->upvec, mat[1]);
+	normalize_v3(evli->upvec);
+
+	light_shape_parameters_set(evli, la, scale);
+
+	/* Lamp Type */
+	evli->lamptype = (float)la->type;
+	if ((la->type == LA_AREA) && ELEM(la->area_shape, LA_AREA_DISK, LA_AREA_ELLIPSE)) {
+		evli->lamptype = LAMPTYPE_AREA_ELLIPSE;
 	}
+
+	power = light_shape_power_get(la, evli);
 	mul_v3_fl(evli->color, power * la->energy);
 
 	/* No shadow by default */
@@ -789,7 +827,7 @@ static void eevee_shadow_cube_setup(Object *ob, EEVEE_LampsInfo *linfo, EEVEE_La
 
 	ubo_data->bias = 0.05f * la->bias;
 	ubo_data->near = la->clipsta;
-	ubo_data->far = la->clipend;
+	ubo_data->far = 1.0f / (evli->invsqrdist * evli->invsqrdist);
 	ubo_data->exp = (linfo->shadow_method == SHADOW_VSM) ? la->bleedbias : la->bleedexp;
 
 	evli->shadowid = (float)(sh_data->shadow_id);
@@ -1180,6 +1218,8 @@ void EEVEE_draw_shadows(EEVEE_ViewLayerData *sldata, EEVEE_Data *vedata)
 	EEVEE_StorageList *stl = vedata->stl;
 	EEVEE_EffectsInfo *effects = stl->effects;
 	EEVEE_LampsInfo *linfo = sldata->lamps;
+	const DRWContextState *draw_ctx = DRW_context_state_get();
+	const float light_threshold = draw_ctx->scene->eevee.light_threshold;
 	Object *ob;
 	int i;
 
@@ -1196,7 +1236,7 @@ void EEVEE_draw_shadows(EEVEE_ViewLayerData *sldata, EEVEE_Data *vedata)
 		Lamp *la = (Lamp *)ob->data;
 		BoundSphere bsphere = {
 			.center = {ob->obmat[3][0], ob->obmat[3][1], ob->obmat[3][2]},
-			.radius = la->clipend
+			.radius = light_attenuation_radius_get(la, light_threshold)
 		};
 		cube_visible[i] = DRW_culling_sphere_test(&bsphere);
 	}
@@ -1236,14 +1276,13 @@ void EEVEE_draw_shadows(EEVEE_ViewLayerData *sldata, EEVEE_Data *vedata)
 		EEVEE_ShadowCubeData *evscd = &led->data.scd;
 		EEVEE_ShadowCube *cube_data = linfo->shadow_cube_data + evscd->cube_id;
 
-		perspective_m4(winmat, -la->clipsta, la->clipsta, -la->clipsta, la->clipsta, la->clipsta, la->clipend);
-
 		srd->clip_near = la->clipsta;
-		srd->clip_far = la->clipend;
-		copy_v3_v3(srd->position, cube_data->position);
-
+		srd->clip_far = light_attenuation_radius_get(la, light_threshold);
 		srd->stored_texel_size = 1.0 / (float)linfo->shadow_cube_store_size;
 		srd->exponent = la->bleedexp;
+		copy_v3_v3(srd->position, cube_data->position);
+
+		perspective_m4(winmat, -srd->clip_near, srd->clip_near, -srd->clip_near, srd->clip_near, srd->clip_near, srd->clip_far);
 
 		DRW_uniformbuffer_update(sldata->shadow_render_ubo, srd);
 
diff --git a/source/blender/draw/engines/eevee/eevee_private.h b/source/blender/draw/engines/eevee/eevee_private.h
index a07f6f05f45..7c431e6685c 100644
--- a/source/blender/draw/engines/eevee/eevee_private.h
+++ b/source/blender/draw/engines/eevee/eevee_private.h
@@ -349,7 +349,7 @@ typedef struct EEVEE_StorageList {
 
 /* ************ LIGHT UBO ************* */
 typedef struct EEVEE_Light {
-	float position[3], dist;
+	float position[3], invsqrdist;
 	float color[3], spec;
 	float spotsize, spotblend, radius, shadowid;
 	float rightvec[3], sizex;
diff --git a/source/blender/draw/engines/eevee/shaders/bsdf_common_lib.glsl b/source/blender/draw/engines/eevee/shaders/bsdf_common_lib.glsl
index eb03df67f6b..a54cefc5b85 100644
--- a/source/blender/draw/engines/eevee/shaders/bsdf_common_lib.glsl
+++ b/source/blender/draw/engines/eevee/shaders/bsdf_common_lib.glsl
@@ -24,7 +24,7 @@ uniform sampler2DArray planarDepth;
 
 /* ------ Lights ----- */
 struct LightData {
-	vec4 position_influence;      /* w : InfluenceRadius */
+	vec4 position_influence;      /* w : InfluenceRadius (inversed and squared) */
 	vec4 color_spec;              /* w : Spec Intensity */
 	vec4 spotdata_radius_shadow;  /* x : spot size, y : spot blend, z : radius, w: shadow id */
 	vec4 rightvec_sizex;          /* xyz: Normalized up vector, w: area size X or spot scale X */
diff --git a/source/blender/draw/engines/eevee/shaders/lamps_lib.glsl b/source/blender/draw/engines/eevee/shaders/lamps_lib.glsl
index ecc1a817dae..b260c6254be 100644
--- a/source/blender/draw/engines/eevee/shaders/lamps_lib.glsl
+++ b/source/blender/draw/engines/eevee/shaders/lamps_lib.glsl
@@ -157,6 +157,15 @@ float shadow_cascade(ShadowData sd, int scd_id, float texid, vec3 W)
 /* --------------------- Light Functions --------------------- */
 /* ----------------------------------------------------------- */
 #define MAX_MULTI_SHADOW 4
+/* From Frostbite PBR Course
+ * Distance based attenuation
+ * http://www.frostbite.com/wp-content/uploads/2014/11/course_notes_moving_frostbite_to_pbr.pdf */
+float distance_attenuation(float dist_sqr, float inv_sqr_influence)
+{
+	float factor = dist_sqr * inv_sqr_influence;
+	float fac = saturate(1.0 - factor * factor);
+	return fac * fac;
+}
 
 float light_visibility(LightData ld, vec3 W,
 #ifndef VOLUMETRICS
@@ -183,6 +192,9 @@ float light_visibility(LightData ld, vec3 W,
 	else if (ld.l_type == AREA_RECT || ld.l_type == AREA_ELLIPSE) {
 		vis *= step(0.0, -dot(l_vector.xyz, ld.l_forward));
 	}
+	if (ld.l_type != SUN) {
+		vis *= distance_attenuation(l_vector.w * l_vector.w, ld.l_influence);
+	}
 
 #if !defined(VOLUMETRICS) || defined(VOLUME_SHADOW)
 	/* shadowing */
@@ -343,6 +355,10 @@ vec3 light_translucent(LightData ld, vec3 W, vec3 N, vec4 l_vector, float scale)
 #else
 	vec3 vis = vec3(1.0);
 
+	if (ld.l_type != SUN) {
+		vis *= distance_attenuation(l_vector.w * l_vector.w, ld.l_influence);
+	}
+
 	/* Only shadowed light can produce translucency */
 	if (ld.l_shadowid >= 0.0) {
 		ShadowData data = shadows_data[int(ld.l_shadowid)];
diff --git a/source/blender/makesdna/DNA_lamp_types.h b/source/blender/makesdna/DNA_lamp_types.h
index f9958abb603..d035e0c5440 100644
--- a/source/blender/makesdna/DNA_lamp_types.h
+++ b/source/blender/makesdna/DNA_lamp_types.h
@@ -86,7 +86,7 @@ typedef struct Lamp {
 
 	float contact_dist, contact_bias, contact_spread, contact_thickness;
 
-	float spec_fac, pad;
+	float spec_fac, att_dist;
 
 	/* preview */
 	struct PreviewImage *preview;
@@ -134,6 +134,7 @@ typedef struct Lamp {
 #define LA_SHOW_CONE    (1 << 17)
 /* #define LA_SHOW_SHADOW_BOX (1 << 18) */
 #define LA_SHAD_CONTACT (1 << 19)
+#define LA_CUSTOM_ATTENUATION (1 << 20)
 
 /* falloff_type */
 #define LA_FALLOFF_CONSTANT			0
diff --git a/source/blender/makesdna/DNA_scene_types.h b/source/blender/makesdna/DNA_scene_types.h
index 1352e28e6c2..c78f622e8bc 100644
--- a/source/blender/makesdna/DNA_scene_types.h
+++ b/source/blender/makesdna/DNA_scene_types.h
@@ -1508,7 +1508,7 @@ typedef struct SceneEEVEE {
 	char light_cache_info[64];
 
 	float overscan;
-	float pad;
+	float light_threshold;
 } SceneEEVEE;
 
 /* *************************************************************** */
diff --git a/source/blender/makesrna/intern/rna_lamp.c b/source/blender/makesrna/intern/rna_lamp.c
index 7828d4a7b7d..11a2c1a5529 100644
--- a/source/blender/makesrna/intern/rna_lamp.c
+++ b/source/blender/makesrna/intern/rna_lamp.c
@@ -164,6 +164,19 @@ static void rna_def_light(BlenderRNA *brna)
 	RNA_def_property_ui_text(prop, "Specular Factor", "Specular reflection multiplier");
 	RNA_def_property_update(prop, 0, "rna_Light_update");
 
+	prop = RNA_def_property(srna, "use_custom_distance", PROP_BOOLEAN, PROP_NONE);
+	RNA_def_property_boolean_sdna(prop, NULL, "mode", LA_CUSTOM_ATTENUATION);
+	RNA_def_property_ui_text(prop, "Custom Attenuation", "Use custom attenuation distance instead of global light threshold");
+	RNA_def_property_update(prop, 0, "rna_Light_update");
+
+	prop = RNA_def_property(srna, "cutoff_distance", PROP_FLOAT, PROP_DISTANCE);
+	RNA_def_property_float_sdna(prop, NULL, "att_dist");
+	RNA_def_property_float_default(prop, 1.0f);
+	RNA_def_property_range(prop, 0.0f, FLT_MAX);
+	RNA_def_property_ui_range(prop, 0.01f, 100.0f, 1.0, 2);
+	RNA_def_property_ui_text(prop, "Cutoff Distance", "Distance at which the light influence will be set to 0");
+	RNA_def_property_update(prop, 0, "rna_Light_update");
+
 	/* nodes */
 	prop = RNA_def_property(srna, "node_tree", PROP_POINTER, PROP_NONE);
 	RNA_def_property_pointer_sdna(prop, NULL, "nodetree");
diff --git a/source/blender/makesrna/intern/rna_scene.c b/source/blender/makesrna/intern/rna_scene.c
index 17513a55e23..123ed562343 100644
--- a/source/blender/makesrna/intern/rna_scene.c
+++ b/source/blender/makesrna/intern/rna_scene.c
@@ -6035,6 +6035,13 @@ static void rna_def_scene_eevee(BlenderRNA *brna)
 	RNA_def_property_ui_text(prop, "Soft Shadows", "Randomize shadowmaps origin to create soft shadows");
 	RNA_def_property_override_flag(prop, PROPOVERRIDE_OVERRIDABLE_STATIC);
 
+	prop = RNA_def_property(srna, "light_threshold", PROP_FLOAT, PROP_UNSIGNED);
+	RNA_def_property_float_default(prop, 0.01f);
+	RNA_def_property_ui_text(prop, "Light Threshold", "Minimum light intensity for a light to contribute to the lighting");
+	RNA_def_property_range(prop, 0.0f, FLT_MAX);
+	RNA_def_property_ui_range(prop, 0.0f, 1.0f, 0.1, 3);
+	RNA_def_property_override_flag(prop, PROPOVERRIDE_OVERRIDABLE_STATIC);
+
 	/* Overscan */
 	prop = RNA_def_property(srna, "use_overscan", PROP_BOOLEAN, PROP_NONE);
 	RNA_def_property_boolean_sdna(prop, NULL, "flag", SCE_EEVEE_OVERSCAN);