4 files changed, 13 insertions, 10 deletions
diff --git a/modules/lightmapper_rd/lightmapper_rd.cpp b/modules/lightmapper_rd/lightmapper_rd.cpp
index f31eb3f066..82aaa492fc 100644
--- a/modules/lightmapper_rd/lightmapper_rd.cpp
+++ b/modules/lightmapper_rd/lightmapper_rd.cpp
@@ -93,8 +93,8 @@ void LightmapperRD::add_spot_light(bool p_static, const Vector3 &p_position, con
 	l.direction[2] = p_direction.z;
 	l.range = p_range;
 	l.attenuation = p_attenuation;
-	l.spot_angle = Math::deg2rad(p_spot_angle);
-	l.spot_attenuation = p_spot_attenuation;
+	l.cos_spot_angle = Math::cos(Math::deg2rad(p_spot_angle));
+	l.inv_spot_attenuation = 1.0f / p_spot_attenuation;
 	l.color[0] = p_color.r;
 	l.color[1] = p_color.g;
 	l.color[2] = p_color.b;
diff --git a/modules/lightmapper_rd/lightmapper_rd.h b/modules/lightmapper_rd/lightmapper_rd.h
index bb735baf6c..1c360bd0ab 100644
--- a/modules/lightmapper_rd/lightmapper_rd.h
+++ b/modules/lightmapper_rd/lightmapper_rd.h
@@ -54,8 +54,8 @@ class LightmapperRD : public Lightmapper {
 		float size;
 		float range;
 		float attenuation;
-		float spot_angle;
-		float spot_attenuation;
+		float cos_spot_angle;
+		float inv_spot_attenuation;
 		uint32_t static_bake;
 		uint32_t pad[3];
 
diff --git a/modules/lightmapper_rd/lm_common_inc.glsl b/modules/lightmapper_rd/lm_common_inc.glsl
index 0ff455936e..f8a0cd16de 100644
--- a/modules/lightmapper_rd/lm_common_inc.glsl
+++ b/modules/lightmapper_rd/lm_common_inc.glsl
@@ -56,8 +56,8 @@ struct Light {
 
 	float range;
 	float attenuation;
-	float spot_angle;
-	float spot_attenuation;
+	float cos_spot_angle;
+	float inv_spot_attenuation;
 
 	bool static_bake;
 	uint pad[3];
diff --git a/modules/lightmapper_rd/lm_compute.glsl b/modules/lightmapper_rd/lm_compute.glsl
index 8a9adbc5cc..eb9d817f99 100644
--- a/modules/lightmapper_rd/lm_compute.glsl
+++ b/modules/lightmapper_rd/lm_compute.glsl
@@ -313,13 +313,16 @@ void main() {
 
 			if (lights.data[i].type == LIGHT_TYPE_SPOT) {
 				vec3 rel = normalize(position - light_pos);
-				float angle = acos(dot(rel, lights.data[i].direction));
-				if (angle > lights.data[i].spot_angle) {
+				float cos_spot_angle = lights.data[i].cos_spot_angle;
+				float cos_angle = dot(rel, lights.data[i].direction);
+
+				if (cos_angle < cos_spot_angle) {
 					continue; //invisible, dont try
 				}
 
-				float d = clamp(angle / lights.data[i].spot_angle, 0, 1);
-				attenuation *= pow(1.0 - d, lights.data[i].spot_attenuation);
+				float scos = max(cos_angle, cos_spot_angle);
+				float spot_rim = max(0.0001, (1.0 - scos) / (1.0 - cos_spot_angle));
+				attenuation *= 1.0 - pow(spot_rim, lights.data[i].inv_spot_attenuation);
 			}
 		}