Draw volumetric clouds, their shadows, a volumetric fog and catalogue stars from a new weather system in the GL 4.6 renderer

shaders/apply_fog.glsl

@@ -1,30 +1,41 @@
+// fog between the camera and a fragment, see fog_volume.glsl and weather_common.glsl. a draw with a fog_density of 0 is not
+// fogged; one with another density than the regular one (the glare of lamps) gets the optical depth scaled by the ratio
+#include <fog_volume.glsl>
+
+// rgb: light the fog adds, a: what it lets through
+vec4 fog_at_fragment()
+{
+	if (fog_density <= 0.0)
+		return vec4(0.0, 0.0, 0.0, 1.0);
+	vec4 fog = fog_along_view(f_pos.xyz, gl_FragCoord.xy);
+	float scale = fog_density / max(fog_light.w, 1e-12);
+	if (abs(scale - 1.0) > 1e-3)
+	{
+		float transmittance = exp(log(max(fog.a, 1e-8)) * scale);
+		fog.rgb *= (1.0 - transmittance) / max(1.0 - fog.a, 1e-4);
+		fog.a = transmittance;
+	}
+	return fog;
+}
+
 vec3 get_fog_color()
 {
-	vec3 fog_color_v = fog_color;
-	if (lights_count >= 1U && lights[0].type == LIGHT_DIR) {
-		float sun_amount = max(dot(normalize(f_pos.xyz), normalize(-lights[0].dir)), 0.0);
-		fog_color_v += lights[0].color * pow(sun_amount, 30.0);
-	}
-	return fog_color_v;
+	vec4 fog = fog_at_fragment();
+	return fog.rgb / max(1.0 - fog.a, 1e-4);
 }
 
 float get_fog_amount()
 {
-	float z = length(f_pos.xyz);
-//	float fog_amount_v = 1.0 - z * fog_density; // linear
-//	float fog_amount_v = exp( -fog_density * z ); // exp
-	float fog_amount_v = exp2( -fog_density * fog_density * z * z * 1.442695 ); // exp2
-
-	fog_amount_v = 1.0 - clamp(fog_amount_v, 0.0, 1.0);
-	return fog_amount_v;
+	return 1.0 - fog_at_fragment().a;
 }
 
 vec3 apply_fog(vec3 color)
 {
-	return mix(color, get_fog_color(), get_fog_amount());
+	vec4 fog = fog_at_fragment();
+	return color * fog.a + fog.rgb;
 }
 
 vec3 add_fog(vec3 color, float amount)
 {
-	return color + get_fog_color() * get_fog_amount() * amount;
+	return color + fog_at_fragment().rgb * amount;
 }