Add Environment properties to control fog rendering on background sky

Values lower than 1.0 can be used to make the fog rendering not fully
obstruct the sky. This can be desired when using fog as a purely
atmospheric effect, without intending to use fog for open world fog
fading.

When set to 0.0, fog rendering behavior will be similar to Godot 3.x
where sky rendering was never affected by fog.

3 files changed, 40 insertions, 33 deletions

diff --git a/servers/rendering/renderer_rd/environment/sky.cpp b/servers/rendering/renderer_rd/environment/sky.cpp
index 1d6b158d65..671fa14900 100644
--- a/servers/rendering/renderer_rd/environment/sky.cpp
+++ b/servers/rendering/renderer_rd/environment/sky.cpp
@@ -1319,6 +1319,9 @@ void SkyRD::setup(RID p_env, RID p_render_buffers, const PagedArray<RID> &p_ligh
 	sky_scene_state.ubo.fog_light_color[2] = fog_color.b * fog_energy;
 	sky_scene_state.ubo.fog_sun_scatter = RendererSceneRenderRD::get_singleton()->environment_get_fog_sun_scatter(p_env);
 
+	sky_scene_state.ubo.fog_sky_affect = RendererSceneRenderRD::get_singleton()->environment_get_fog_sky_affect(p_env);
+	sky_scene_state.ubo.volumetric_fog_sky_affect = RendererSceneRenderRD::get_singleton()->environment_get_volumetric_fog_sky_affect(p_env);
+
 	RD::get_singleton()->buffer_update(sky_scene_state.uniform_buffer, 0, sizeof(SkySceneState::UBO), &sky_scene_state.ubo);
 }
 
diff --git a/servers/rendering/renderer_rd/environment/sky.h b/servers/rendering/renderer_rd/environment/sky.h
index 080165c112..3534e9b571 100644
--- a/servers/rendering/renderer_rd/environment/sky.h
+++ b/servers/rendering/renderer_rd/environment/sky.h
@@ -148,20 +148,23 @@ private:
 public:
 	struct SkySceneState {
 		struct UBO {
-			uint32_t volumetric_fog_enabled;
-			float volumetric_fog_inv_length;
-			float volumetric_fog_detail_spread;
-
-			float fog_aerial_perspective;
-
-			float fog_light_color[3];
-			float fog_sun_scatter;
-
-			uint32_t fog_enabled;
-			float fog_density;
-
-			float z_far;
-			uint32_t directional_light_count;
+			uint32_t volumetric_fog_enabled; // 4 - 4
+			float volumetric_fog_inv_length; // 4 - 8
+			float volumetric_fog_detail_spread; // 4 - 12
+			float volumetric_fog_sky_affect; // 4 - 16
+
+			uint32_t fog_enabled; // 4 - 20
+			float fog_sky_affect; // 4 - 24
+			float fog_density; // 4 - 28
+			float fog_sun_scatter; // 4 - 32
+
+			float fog_light_color[3]; // 12 - 44
+			float fog_aerial_perspective; // 4 - 48
+
+			float z_far; // 4 - 52
+			uint32_t directional_light_count; // 4 - 56
+			uint32_t pad1; // 4 - 60
+			uint32_t pad2; // 4 - 64
 		};
 
 		UBO ubo;
diff --git a/servers/rendering/renderer_rd/shaders/environment/sky.glsl b/servers/rendering/renderer_rd/shaders/environment/sky.glsl
index e825020a4e..a993e66682 100644
--- a/servers/rendering/renderer_rd/shaders/environment/sky.glsl
+++ b/servers/rendering/renderer_rd/shaders/environment/sky.glsl
@@ -83,20 +83,23 @@ layout(set = 0, binding = 1, std430) restrict readonly buffer GlobalShaderUnifor
 global_shader_uniforms;
 
 layout(set = 0, binding = 2, std140) uniform SceneData {
-	bool volumetric_fog_enabled;
-	float volumetric_fog_inv_length;
-	float volumetric_fog_detail_spread;
-
-	float fog_aerial_perspective;
-
-	vec3 fog_light_color;
-	float fog_sun_scatter;
-
-	bool fog_enabled;
-	float fog_density;
-
-	float z_far;
-	uint directional_light_count;
+	bool volumetric_fog_enabled; // 4 - 4
+	float volumetric_fog_inv_length; // 4 - 8
+	float volumetric_fog_detail_spread; // 4 - 12
+	float volumetric_fog_sky_affect; // 4 - 16
+
+	bool fog_enabled; // 4 - 20
+	float fog_sky_affect; // 4 - 24
+	float fog_density; // 4 - 28
+	float fog_sun_scatter; // 4 - 32
+
+	vec3 fog_light_color; // 12 - 44
+	float fog_aerial_perspective; // 4 - 48
+
+	float z_far; // 4 - 52
+	uint directional_light_count; // 4 - 56
+	uint pad1; // 4 - 60
+	uint pad2; // 4 - 64
 }
 scene_data;
 
@@ -169,9 +172,7 @@ vec4 fog_process(vec3 view, vec3 sky_color) {
 		}
 	}
 
-	float fog_amount = clamp(1.0 - exp(-scene_data.z_far * scene_data.fog_density), 0.0, 1.0);
-
-	return vec4(fog_color, fog_amount);
+	return vec4(fog_color, 1.0);
 }
 
 void main() {
@@ -228,12 +229,12 @@ void main() {
 	// Draw "fixed" fog before volumetric fog to ensure volumetric fog can appear in front of the sky.
 	if (scene_data.fog_enabled) {
 		vec4 fog = fog_process(cube_normal, frag_color.rgb);
-		frag_color.rgb = mix(frag_color.rgb, fog.rgb, fog.a);
+		frag_color.rgb = mix(frag_color.rgb, fog.rgb, fog.a * scene_data.fog_sky_affect);
 	}
 
 	if (scene_data.volumetric_fog_enabled) {
 		vec4 fog = volumetric_fog_process(uv);
-		frag_color.rgb = mix(frag_color.rgb, fog.rgb, fog.a);
+		frag_color.rgb = mix(frag_color.rgb, fog.rgb, fog.a * scene_data.volumetric_fog_sky_affect);
 	}
 
 	if (custom_fog.a > 0.0) {