Fix some SpotLight3D issues (clustering artifacts, light leak)

drivers/gles3/shaders/scene.glsl

@@ -690,7 +690,8 @@ void light_compute(vec3 N, vec3 L, vec3 V, float A, vec3 light_color, float atte
 #endif
 
 #if defined(LIGHT_RIM_USED)
-		float rim_light = pow(max(0.0, 1.0 - cNdotV), max(0.0, (1.0 - roughness) * 16.0));
+		// Epsilon min to prevent pow(0, 0) singularity which results in undefined behavior.
+		float rim_light = pow(max(1e-4, 1.0 - cNdotV), max(0.0, (1.0 - roughness) * 16.0));
 		diffuse_light += rim_light * rim * mix(vec3(1.0), albedo, rim_tint) * light_color;
 #endif
 	}

scene/3d/light_3d.cpp

@@ -157,9 +157,16 @@ AABB Light3D::get_aabb() const {
 		return AABB(Vector3(-1, -1, -1) * param[PARAM_RANGE], Vector3(2, 2, 2) * param[PARAM_RANGE]);
 
 	} else if (type == RenderingServer::LIGHT_SPOT) {
-		real_t len = param[PARAM_RANGE];
+		real_t cone_slant_height = param[PARAM_RANGE];
-		real_t size = Math::tan(Math::deg_to_rad(param[PARAM_SPOT_ANGLE])) * len;
+		real_t cone_angle_rad = Math::deg_to_rad(param[PARAM_SPOT_ANGLE]);
-		return AABB(Vector3(-size, -size, -len), Vector3(size * 2, size * 2, len));
+
+		if (cone_angle_rad > Math_PI / 2.0) {
+			// Just return the AABB of an omni light if the spot angle is above 90 degrees.
+			return AABB(Vector3(-1, -1, -1) * cone_slant_height, Vector3(2, 2, 2) * cone_slant_height);
+		}
+
+		real_t size = Math::sin(cone_angle_rad) * cone_slant_height;
+		return AABB(Vector3(-size, -size, -cone_slant_height), Vector3(2 * size, 2 * size, cone_slant_height));
 	}
 
 	return AABB();

servers/rendering/renderer_rd/cluster_builder_rd.cpp

@@ -74,7 +74,7 @@ ClusterBuilderSharedDataRD::ClusterBuilderSharedDataRD() {
 		cluster_debug.shader_pipeline = RD::get_singleton()->compute_pipeline_create(cluster_debug.shader);
 	}
 
-	{ // SPHERE
+	{ // Sphere mesh data.
 		static const uint32_t icosphere_vertex_count = 42;
 		static const float icosphere_vertices[icosphere_vertex_count * 3] = {
 			0, 0, -1, 0.7236073, -0.5257253, -0.4472195, -0.276388, -0.8506492, -0.4472199, -0.8944262, 0, -0.4472156, -0.276388, 0.8506492, -0.4472199, 0.7236073, 0.5257253, -0.4472195, 0.276388, -0.8506492, 0.4472199, -0.7236073, -0.5257253, 0.4472195, -0.7236073, 0.5257253, 0.4472195, 0.276388, 0.8506492, 0.4472199, 0.8944262, 0, 0.4472156, 0, 0, 1, -0.1624555, -0.4999952, -0.8506544, 0.4253227, -0.3090114, -0.8506542, 0.2628688, -0.8090116, -0.5257377, 0.8506479, 0, -0.5257359, 0.4253227, 0.3090114, -0.8506542, -0.5257298, 0, -0.8506517, -0.6881894, -0.4999969, -0.5257362, -0.1624555, 0.4999952, -0.8506544, -0.6881894, 0.4999969, -0.5257362, 0.2628688, 0.8090116, -0.5257377, 0.9510579, -0.3090126, 0, 0.9510579, 0.3090126, 0, 0, -1, 0, 0.5877856, -0.8090167, 0, -0.9510579, -0.3090126, 0, -0.5877856, -0.8090167, 0, -0.5877856, 0.8090167, 0, -0.9510579, 0.3090126, 0, 0.5877856, 0.8090167, 0, 0, 1, 0, 0.6881894, -0.4999969, 0.5257362, -0.2628688, -0.8090116, 0.5257377, -0.8506479, 0, 0.5257359, -0.2628688, 0.8090116, 0.5257377, 0.6881894, 0.4999969, 0.5257362, 0.1624555, -0.4999952, 0.8506544, 0.5257298, 0, 0.8506517, -0.4253227, -0.3090114, 0.8506542, -0.4253227, 0.3090114, 0.8506542, 0.1624555, 0.4999952, 0.8506544
@@ -118,7 +118,7 @@ ClusterBuilderSharedDataRD::ClusterBuilderSharedDataRD() {
 		sphere_overfit = 1.0 / min_d;
 	}
 
-	{ // CONE
+	{ // Cone mesh data.
 		static const uint32_t cone_vertex_count = 99;
 		static const float cone_vertices[cone_vertex_count * 3] = {
 			0, 1, -1, 0.1950903, 0.9807853, -1, 0.3826835, 0.9238795, -1, 0.5555703, 0.8314696, -1, 0.7071068, 0.7071068, -1, 0.8314697, 0.5555702, -1, 0.9238795, 0.3826834, -1, 0.9807853, 0.1950903, -1, 1, 0, -1, 0.9807853, -0.1950902, -1, 0.9238796, -0.3826833, -1, 0.8314697, -0.5555702, -1, 0.7071068, -0.7071068, -1, 0.5555702, -0.8314697, -1, 0.3826833, -0.9238796, -1, 0.1950901, -0.9807853, -1, -3.25841e-7, -1, -1, -0.1950907, -0.9807852, -1, -0.3826839, -0.9238793, -1, -0.5555707, -0.8314693, -1, -0.7071073, -0.7071063, -1, -0.83147, -0.5555697, -1, -0.9238799, -0.3826827, -1, 0, 0, 0, -0.9807854, -0.1950894, -1, -1, 9.65599e-7, -1, -0.9807851, 0.1950913, -1, -0.9238791, 0.3826845, -1, -0.8314689, 0.5555713, -1, -0.7071059, 0.7071077, -1, -0.5555691, 0.8314704, -1, -0.3826821, 0.9238801, -1, -0.1950888, 0.9807856, -1
@@ -172,7 +172,7 @@ ClusterBuilderSharedDataRD::ClusterBuilderSharedDataRD() {
 		cone_overfit = 1.0 / min_d;
 	}
 
-	{ // BOX
+	{ // Box mesh data.
 		static const uint32_t box_vertex_count = 8;
 		static const float box_vertices[box_vertex_count * 3] = {
 			-1, -1, -1, -1, -1, 1, -1, 1, -1, -1, 1, 1, 1, -1, -1, 1, -1, 1, 1, 1, -1, 1, 1, 1
@@ -219,8 +219,9 @@ ClusterBuilderSharedDataRD::~ClusterBuilderSharedDataRD() {
 
 void ClusterBuilderRD::_clear() {
 	if (cluster_buffer.is_null()) {
-		return; //nothing to clear
+		return;
 	}
+
 	RD::get_singleton()->free(cluster_buffer);
 	RD::get_singleton()->free(cluster_render_buffer);
 	RD::get_singleton()->free(element_buffer);
@@ -254,7 +255,7 @@ void ClusterBuilderRD::setup(Size2i p_screen_size, uint32_t p_max_elements, RID
 	cluster_screen_size.height = (p_screen_size.height - 1) / cluster_size + 1;
 
 	max_elements_by_type = p_max_elements;
-	if (max_elements_by_type % 32) { //need to be 32 aligned
+	if (max_elements_by_type % 32) { // Needs to be aligned to 32.
 		max_elements_by_type += 32 - (max_elements_by_type % 32);
 	}
 
@@ -264,7 +265,8 @@ void ClusterBuilderRD::setup(Size2i p_screen_size, uint32_t p_max_elements, RID
 
 	uint32_t element_tag_bits_size = render_element_max / 32;
 	uint32_t element_tag_depth_bits_size = render_element_max;
-	cluster_render_buffer_size = cluster_screen_size.x * cluster_screen_size.y * (element_tag_bits_size + element_tag_depth_bits_size) * 4; // tag bits (element was used) and tag depth (depth range in which it was used)
+
+	cluster_render_buffer_size = cluster_screen_size.x * cluster_screen_size.y * (element_tag_bits_size + element_tag_depth_bits_size) * 4; // Tag bits (element was used) and tag depth (depth range in which it was used).
 
 	cluster_render_buffer = RD::get_singleton()->storage_buffer_create(cluster_render_buffer_size);
 	cluster_buffer = RD::get_singleton()->storage_buffer_create(cluster_buffer_size);
@@ -379,9 +381,9 @@ void ClusterBuilderRD::begin(const Transform3D &p_view_transform, const Projecti
 	projection = p_cam_projection;
 	z_near = projection.get_z_near();
 	z_far = projection.get_z_far();
-	orthogonal = p_cam_projection.is_orthogonal();
+	camera_orthogonal = p_cam_projection.is_orthogonal();
 	adjusted_projection = projection;
-	if (!orthogonal) {
+	if (!camera_orthogonal) {
 		adjusted_projection.adjust_perspective_znear(0.0001);
 	}
 
@@ -390,7 +392,7 @@ void ClusterBuilderRD::begin(const Transform3D &p_view_transform, const Projecti
 	projection = correction * projection;
 	adjusted_projection = correction * adjusted_projection;
 
-	//reset counts
+	// Reset counts.
 	render_element_count = 0;
 	for (uint32_t i = 0; i < ELEMENT_TYPE_MAX; i++) {
 		cluster_count_by_type[i] = 0;
@@ -402,14 +404,14 @@ void ClusterBuilderRD::bake_cluster() {
 
 	RD::get_singleton()->draw_command_begin_label("Bake Light Cluster");
 
-	//clear cluster buffer
+	// Clear cluster buffer.
 	RD::get_singleton()->buffer_clear(cluster_buffer, 0, cluster_buffer_size, RD::BARRIER_MASK_RASTER | RD::BARRIER_MASK_COMPUTE);
 
 	if (render_element_count > 0) {
-		//clear render buffer
+		// Clear render buffer.
 		RD::get_singleton()->buffer_clear(cluster_render_buffer, 0, cluster_render_buffer_size, RD::BARRIER_MASK_RASTER);
 
-		{ //fill state uniform
+		{ // Fill state uniform.
 
 			StateUniform state;
 
@@ -425,13 +427,13 @@ void ClusterBuilderRD::bake_cluster() {
 			RD::get_singleton()->buffer_update(state_uniform, 0, sizeof(StateUniform), &state, RD::BARRIER_MASK_RASTER | RD::BARRIER_MASK_COMPUTE);
 		}
 
-		//update instances
+		// Update instances.
 
 		RD::get_singleton()->buffer_update(element_buffer, 0, sizeof(RenderElementData) * render_element_count, render_elements, RD::BARRIER_MASK_RASTER | RD::BARRIER_MASK_COMPUTE);
 
 		RENDER_TIMESTAMP("Render 3D Cluster Elements");
 
-		//render elements
+		// Render elements.
 		{
 			RD::DrawListID draw_list = RD::get_singleton()->draw_list_begin(framebuffer, RD::INITIAL_ACTION_DROP, RD::FINAL_ACTION_DISCARD, RD::INITIAL_ACTION_DROP, RD::FINAL_ACTION_DISCARD);
 			ClusterBuilderSharedDataRD::ClusterRender::PushConstant push_constant = {};
@@ -447,8 +449,16 @@ void ClusterBuilderRD::bake_cluster() {
 						RD::get_singleton()->draw_list_bind_index_array(draw_list, shared->sphere_index_array);
 					} break;
 					case ELEMENT_TYPE_SPOT_LIGHT: {
+						// If the spot angle is above a certain threshold, use a sphere instead of a cone for building the clusters
+						// since the cone gets too flat/large (spot angle close to 90 degrees) or
+						// can't even cover the affected area of the light (spot angle above 90 degrees).
+						if (render_elements[i].has_wide_spot_angle) {
+							RD::get_singleton()->draw_list_bind_vertex_array(draw_list, shared->sphere_vertex_array);
+							RD::get_singleton()->draw_list_bind_index_array(draw_list, shared->sphere_index_array);
+						} else {
 							RD::get_singleton()->draw_list_bind_vertex_array(draw_list, shared->cone_vertex_array);
 							RD::get_singleton()->draw_list_bind_index_array(draw_list, shared->cone_index_array);
+						}
 					} break;
 					case ELEMENT_TYPE_DECAL:
 					case ELEMENT_TYPE_REFLECTION_PROBE: {
@@ -465,7 +475,7 @@ void ClusterBuilderRD::bake_cluster() {
 			}
 			RD::get_singleton()->draw_list_end(RD::BARRIER_MASK_COMPUTE);
 		}
-		//store elements
+		// Store elements.
 		RENDER_TIMESTAMP("Pack 3D Cluster Elements");
 
 		{
@@ -509,7 +519,7 @@ void ClusterBuilderRD::debug(ElementType p_element) {
 	push_constant.cluster_screen_size[1] = cluster_screen_size.y;
 	push_constant.cluster_shift = get_shift_from_power_of_2(cluster_size);
 	push_constant.cluster_type = p_element;
-	push_constant.orthogonal = orthogonal;
+	push_constant.orthogonal = camera_orthogonal;
 	push_constant.z_far = z_far;
 	push_constant.z_near = z_near;
 	push_constant.max_cluster_element_count_div_32 = max_elements_by_type / 32;

servers/rendering/renderer_rd/cluster_builder_rd.h

@@ -43,13 +43,13 @@ class ClusterBuilderSharedDataRD {
 	RID sphere_vertex_array;
 	RID sphere_index_buffer;
 	RID sphere_index_array;
-	float sphere_overfit = 0.0; //because an icosphere is not a perfect sphere, we need to enlarge it to cover the sphere area
+	float sphere_overfit = 0.0; // Because an icosphere is not a perfect sphere, we need to enlarge it to cover the sphere area.
 
 	RID cone_vertex_buffer;
 	RID cone_vertex_array;
 	RID cone_index_buffer;
 	RID cone_index_array;
-	float cone_overfit = 0.0; //because an cone mesh is not a perfect sphere, we need to enlarge it to cover the actual cone area
+	float cone_overfit = 0.0; // Because an cone mesh is not a perfect cone, we need to enlarge it to cover the actual cone area.
 
 	RID box_vertex_buffer;
 	RID box_vertex_array;
@@ -73,6 +73,7 @@ class ClusterBuilderSharedDataRD {
 		ClusterRenderShaderRD cluster_render_shader;
 		RID shader_version;
 		RID shader;
+
 		enum PipelineVersion {
 			PIPELINE_NORMAL,
 			PIPELINE_MSAA,
@@ -85,10 +86,11 @@ class ClusterBuilderSharedDataRD {
 	struct ClusterStore {
 		struct PushConstant {
 			uint32_t cluster_render_data_size; // how much data for a single cluster takes
-			uint32_t max_render_element_count_div_32; //divided by 32
+			uint32_t max_render_element_count_div_32; // divided by 32
 			uint32_t cluster_screen_size[2];
-			uint32_t render_element_count_div_32; //divided by 32
+			uint32_t render_element_count_div_32; // divided by 32
-			uint32_t max_cluster_element_count_div_32; //divided by 32
+			uint32_t max_cluster_element_count_div_32; // divided by 32
+
 			uint32_t pad1;
 			uint32_t pad2;
 		};
@@ -111,6 +113,7 @@ class ClusterBuilderSharedDataRD {
 
 			uint32_t orthogonal;
 			uint32_t max_cluster_element_count_div_32;
+
 			uint32_t pad1;
 			uint32_t pad2;
 		};
@@ -128,6 +131,8 @@ public:
 
 class ClusterBuilderRD {
 public:
+	static constexpr float WIDE_SPOT_ANGLE_THRESHOLD_DEG = 60.0f;
+
 	enum LightType {
 		LIGHT_TYPE_OMNI,
 		LIGHT_TYPE_SPOT
@@ -144,21 +149,20 @@ public:
 		ELEMENT_TYPE_DECAL,
 		ELEMENT_TYPE_REFLECTION_PROBE,
 		ELEMENT_TYPE_MAX,
-
 	};
 
 private:
 	ClusterBuilderSharedDataRD *shared = nullptr;
 
 	struct RenderElementData {
-		uint32_t type; //0-4
+		uint32_t type; // 0-4
 		uint32_t touches_near;
 		uint32_t touches_far;
 		uint32_t original_index;
-		float transform_inv[12]; //transposed transform for less space
+		float transform_inv[12]; // Transposed transform for less space.
 		float scale[3];
-		uint32_t pad;
+		uint32_t has_wide_spot_angle;
-	};
+	}; // Keep aligned to 32 bytes.
 
 	uint32_t cluster_count_by_type[ELEMENT_TYPE_MAX] = {};
 	uint32_t max_elements_by_type = 0;
@@ -172,7 +176,7 @@ private:
 	Projection projection;
 	float z_far = 0;
 	float z_near = 0;
-	bool orthogonal = false;
+	bool camera_orthogonal = false;
 
 	enum Divisor {
 		DIVISOR_1,
@@ -188,26 +192,27 @@ private:
 	Size2i cluster_screen_size;
 
 	RID framebuffer;
-	RID cluster_render_buffer; //used for creating
+	RID cluster_render_buffer; // Used for creating.
-	RID cluster_buffer; //used for rendering
+	RID cluster_buffer; // Used for rendering.
-	RID element_buffer; //used for storing, to hint element touches far plane or near plane
+	RID element_buffer; // Used for storing, to hint element touches far plane or near plane.
 	uint32_t cluster_render_buffer_size = 0;
 	uint32_t cluster_buffer_size = 0;
 
 	RID cluster_render_uniform_set;
 	RID cluster_store_uniform_set;
 
-	//persistent data
+	// Persistent data.
 
 	void _clear();
 
 	struct StateUniform {
 		float projection[16];
 		float inv_z_far;
-		uint32_t screen_to_clusters_shift; // shift to obtain coordinates in block indices
+		uint32_t screen_to_clusters_shift; // Shift to obtain coordinates in block indices.
-		uint32_t cluster_screen_width; //
+		uint32_t cluster_screen_width;
-		uint32_t cluster_data_size; // how much data for a single cluster takes
+		uint32_t cluster_data_size; // How much data is needed for a single cluster.
 		uint32_t cluster_depth_offset;
+
 		uint32_t pad0;
 		uint32_t pad1;
 		uint32_t pad2;
@@ -224,10 +229,10 @@ public:
 
 	_FORCE_INLINE_ void add_light(LightType p_type, const Transform3D &p_transform, float p_radius, float p_spot_aperture) {
 		if (p_type == LIGHT_TYPE_OMNI && cluster_count_by_type[ELEMENT_TYPE_OMNI_LIGHT] == max_elements_by_type) {
-			return; //max number elements reached
+			return; // Max number elements reached.
 		}
 		if (p_type == LIGHT_TYPE_SPOT && cluster_count_by_type[ELEMENT_TYPE_SPOT_LIGHT] == max_elements_by_type) {
-			return; //max number elements reached
+			return; // Max number elements reached.
 		}
 
 		RenderElementData &e = render_elements[render_element_count];
@@ -242,15 +247,14 @@ public:
 		radius *= p_radius;
 
 		if (p_type == LIGHT_TYPE_OMNI) {
-			radius *= shared->sphere_overfit; // overfit icosphere
+			radius *= shared->sphere_overfit; // Overfit icosphere.
 
-			//omni
 			float depth = -xform.origin.z;
-			if (orthogonal) {
+			if (camera_orthogonal) {
 				e.touches_near = (depth - radius) < z_near;
 			} else {
-				//contains camera inside light
+				// Contains camera inside light.
-				float radius2 = radius * shared->sphere_overfit; // overfit again for outer size (camera may be outside actual sphere but behind an icosphere vertex)
+				float radius2 = radius * shared->sphere_overfit; // Overfit again for outer size (camera may be outside actual sphere but behind an icosphere vertex)
 				e.touches_near = xform.origin.length_squared() < radius2 * radius2;
 			}
 
@@ -265,12 +269,11 @@ public:
 
 			cluster_count_by_type[ELEMENT_TYPE_OMNI_LIGHT]++;
 
-		} else {
+		} else /*LIGHT_TYPE_SPOT */ {
-			//spot
+			radius *= shared->cone_overfit; // Overfit icosphere
-			radius *= shared->cone_overfit; // overfit icosphere
 
 			real_t len = Math::tan(Math::deg_to_rad(p_spot_aperture)) * radius;
-			//approximate, probably better to use a cone support function
+			// Approximate, probably better to use a cone support function.
 			float max_d = -1e20;
 			float min_d = 1e20;
 #define CONE_MINMAX(m_x, m_y)                                             \
@@ -285,14 +288,13 @@ public:
 			CONE_MINMAX(-1, -1);
 			CONE_MINMAX(1, -1);
 
-			if (orthogonal) {
+			if (camera_orthogonal) {
 				e.touches_near = min_d < z_near;
 			} else {
-				//contains camera inside light
 				Plane base_plane(-xform.basis.get_column(Vector3::AXIS_Z), xform.origin);
 				float dist = base_plane.distance_to(Vector3());
 				if (dist >= 0 && dist < radius) {
-					//inside, check angle
+					// Contains camera inside light, check angle.
 					float angle = Math::rad_to_deg(Math::acos((-xform.origin.normalized()).dot(-xform.basis.get_column(Vector3::AXIS_Z))));
 					e.touches_near = angle < p_spot_aperture * 1.05; //overfit aperture a little due to cone overfit
 				} else {
@@ -302,12 +304,23 @@ public:
 
 			e.touches_far = max_d > z_far;
 
+			// If the spot angle is above the threshold, use a sphere instead of a cone for building the clusters
+			// since the cone gets too flat/large (spot angle close to 90 degrees) or
+			// can't even cover the affected area of the light (spot angle above 90 degrees).
+			if (p_spot_aperture > WIDE_SPOT_ANGLE_THRESHOLD_DEG) {
+				e.scale[0] = radius;
+				e.scale[1] = radius;
+				e.scale[2] = radius;
+				e.has_wide_spot_angle = true;
+			} else {
 				e.scale[0] = len * shared->cone_overfit;
 				e.scale[1] = len * shared->cone_overfit;
 				e.scale[2] = radius;
+				e.has_wide_spot_angle = false;
+			}
 
 			e.type = ELEMENT_TYPE_SPOT_LIGHT;
-			e.original_index = cluster_count_by_type[ELEMENT_TYPE_SPOT_LIGHT]; //use omni since they share index
+			e.original_index = cluster_count_by_type[ELEMENT_TYPE_SPOT_LIGHT]; // Use omni light since they share index.
 
 			RendererRD::MaterialStorage::store_transform_transposed_3x4(xform, e.transform_inv);
 
@@ -319,16 +332,16 @@ public:
 
 	_FORCE_INLINE_ void add_box(BoxType p_box_type, const Transform3D &p_transform, const Vector3 &p_half_extents) {
 		if (p_box_type == BOX_TYPE_DECAL && cluster_count_by_type[ELEMENT_TYPE_DECAL] == max_elements_by_type) {
-			return; //max number elements reached
+			return; // Max number elements reached.
 		}
 		if (p_box_type == BOX_TYPE_REFLECTION_PROBE && cluster_count_by_type[ELEMENT_TYPE_REFLECTION_PROBE] == max_elements_by_type) {
-			return; //max number elements reached
+			return; // Max number elements reached.
 		}
 
 		RenderElementData &e = render_elements[render_element_count];
 		Transform3D xform = view_xform * p_transform;
 
-		//extract scale and scale the matrix by it, makes things simpler
+		// Extract scale and scale the matrix by it, makes things simpler.
 		Vector3 scale = p_half_extents;
 		for (uint32_t i = 0; i < 3; i++) {
 			float s = xform.basis.rows[i].length();
@@ -339,10 +352,10 @@ public:
 		float box_depth = Math::abs(xform.basis.xform_inv(Vector3(0, 0, -1)).dot(scale));
 		float depth = -xform.origin.z;
 
-		if (orthogonal) {
+		if (camera_orthogonal) {
 			e.touches_near = depth - box_depth < z_near;
 		} else {
-			//contains camera inside box
+			// Contains camera inside box.
 			Vector3 inside = xform.xform_inv(Vector3(0, 0, 0)).abs();
 			e.touches_near = inside.x < scale.x && inside.y < scale.y && inside.z < scale.z;
 		}

servers/rendering/renderer_rd/shaders/scene_forward_lights_inc.glsl

@@ -794,8 +794,13 @@ void light_process_spot(uint idx, vec3 vertex, vec3 eye_vec, vec3 normal, vec3 v
 	float light_length = length(light_rel_vec);
 	float spot_attenuation = get_omni_attenuation(light_length, spot_lights.data[idx].inv_radius, spot_lights.data[idx].attenuation);
 	vec3 spot_dir = spot_lights.data[idx].direction;
-	float scos = max(dot(-normalize(light_rel_vec), spot_dir), spot_lights.data[idx].cone_angle);
+
-	float spot_rim = max(0.0001, (1.0 - scos) / (1.0 - spot_lights.data[idx].cone_angle));
+	// This conversion to a highp float is crucial to prevent light leaking
+	// due to precision errors in the following calculations (cone angle is mediump).
+	highp float cone_angle = spot_lights.data[idx].cone_angle;
+	float scos = max(dot(-normalize(light_rel_vec), spot_dir), cone_angle);
+	float spot_rim = max(0.0001, (1.0 - scos) / (1.0 - cone_angle));
+
 	spot_attenuation *= 1.0 - pow(spot_rim, spot_lights.data[idx].cone_attenuation);
 	float light_attenuation = spot_attenuation;
 	vec3 color = spot_lights.data[idx].color;