Fix the height fog effect

doc/classes/Environment.xml

@@ -101,8 +101,10 @@
 			If [code]true[/code], fog effects are enabled.
 		</member>
 		<member name="fog_height" type="float" setter="set_fog_height" getter="get_fog_height" default="0.0">
+			The height at which the height fog effect begins.
 		</member>
 		<member name="fog_height_density" type="float" setter="set_fog_height_density" getter="get_fog_height_density" default="0.0">
+			The density used to increase fog as height decreases. To make fog increase as height increases, use a negative value.
 		</member>
 		<member name="fog_light_color" type="Color" setter="set_fog_light_color" getter="get_fog_light_color" default="Color(0.5, 0.6, 0.7, 1)">
 		</member>

scene/resources/environment.cpp

@@ -1291,7 +1291,7 @@ void Environment::_bind_methods() {
 	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "fog_density", PROPERTY_HINT_RANGE, "0,16,0.0001"), "set_fog_density", "get_fog_density");
 	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "fog_aerial_perspective", PROPERTY_HINT_RANGE, "0,1,0.001"), "set_fog_aerial_perspective", "get_fog_aerial_perspective");
 	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "fog_height", PROPERTY_HINT_RANGE, "-1024,1024,0.01,or_lesser,or_greater"), "set_fog_height", "get_fog_height");
-	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "fog_height_density", PROPERTY_HINT_RANGE, "0,128,0.001,or_greater"), "set_fog_height_density", "get_fog_height_density");
+	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "fog_height_density", PROPERTY_HINT_RANGE, "-16,16,0.0001,or_lesser,or_greater"), "set_fog_height_density", "get_fog_height_density");
 
 	ClassDB::bind_method(D_METHOD("set_volumetric_fog_enabled", "enabled"), &Environment::set_volumetric_fog_enabled);
 	ClassDB::bind_method(D_METHOD("is_volumetric_fog_enabled"), &Environment::is_volumetric_fog_enabled);

servers/rendering/renderer_rd/shaders/scene_forward_clustered.glsl

@@ -526,12 +526,12 @@ vec4 fog_process(vec3 vertex) {
 
 	float fog_amount = 1.0 - exp(min(0.0, -length(vertex) * scene_data.fog_density));
 
-	if (abs(scene_data.fog_height_density) > 0.001) {
+	if (abs(scene_data.fog_height_density) >= 0.0001) {
 		float y = (scene_data.camera_matrix * vec4(vertex, 1.0)).y;
 
-		float y_dist = scene_data.fog_height - y;
+		float y_dist = y - scene_data.fog_height;
 
-		float vfog_amount = clamp(exp(y_dist * scene_data.fog_height_density), 0.0, 1.0);
+		float vfog_amount = clamp(1.0 - exp(y_dist * scene_data.fog_height_density), 0.0, 1.0);
 
 		fog_amount = max(vfog_amount, fog_amount);
 	}

servers/rendering/renderer_rd/shaders/scene_forward_mobile.glsl

@@ -552,12 +552,12 @@ vec4 fog_process(vec3 vertex) {
 
 	float fog_amount = 1.0 - exp(min(0.0, -length(vertex) * scene_data.fog_density));
 
-	if (abs(scene_data.fog_height_density) > 0.001) {
+	if (abs(scene_data.fog_height_density) >= 0.0001) {
 		float y = (scene_data.camera_matrix * vec4(vertex, 1.0)).y;
 
-		float y_dist = scene_data.fog_height - y;
+		float y_dist = y - scene_data.fog_height;
 
-		float vfog_amount = clamp(exp(y_dist * scene_data.fog_height_density), 0.0, 1.0);
+		float vfog_amount = clamp(1.0 - exp(y_dist * scene_data.fog_height_density), 0.0, 1.0);
 
 		fog_amount = max(vfog_amount, fog_amount);
 	}