Horizon blur and noise modulation model based on aloft visibility and weather variability for Atmospheric Light Scattering

Effects/skydome.eff

@@ -14,6 +14,7 @@
     <terminator><use>/environment/terminator-relative-position-m</use></terminator>
     <terrain_alt><use>/environment/mean-terrain-elevation-m</use></terrain_alt>
     <cloud_self_shading><use>/environment/cloud-self-shading</use></cloud_self_shading>
+    <horizon_roughness><use>/local-weather/config/small-scale-persistence</use></horizon_roughness>
   </parameters>
   <technique n="8">
     <predicate>
@@ -102,6 +103,11 @@
         <type>float</type>
         <value><use>cloud_self_shading</use></value>
       </uniform>
+      <uniform>
+        <name>horizon_roughness</name>
+        <type>float</type>
+        <value><use>horizon_roughness</use></value>
+      </uniform>
     </pass>
   </technique>
 

Shaders/skydome.frag

@@ -10,7 +10,7 @@ varying vec3 mie;
 varying vec3 eye;
 varying vec3 hazeColor;
 varying float ct;
-//varying float cosphi;
+varying float cphi;
 varying float delta_z;
 varying float alt;
 varying float earthShade;
@@ -21,6 +21,7 @@ uniform float visibility;
 uniform float avisibility;
 uniform float scattering;
 uniform float cloud_self_shading;
+uniform float horizon_roughness;
 
 const float EarthRadius = 5800000.0;
 
@@ -41,7 +42,39 @@ float rayleighPhase(in float cosTheta)
   return 1.5 * (2.0 + 0.5*cosTheta*cosTheta);
 }
  
+float rand2D(in vec2 co){
+    return fract(sin(dot(co.xy ,vec2(12.9898,78.233))) * 43758.5453);
+}
 
+float simple_interpolate(in float a, in float b, in float x)
+{
+return a + smoothstep(0.0,1.0,x) * (b-a);
+}
+
+float interpolatedNoise2D(in float x, in float y)
+{
+      float integer_x    = x - fract(x);
+      float fractional_x = x - integer_x;
+
+      float integer_y    = y - fract(y);
+      float fractional_y = y - integer_y;
+
+      float v1 = rand2D(vec2(integer_x, integer_y));
+      float v2 = rand2D(vec2(integer_x+1.0, integer_y));
+      float v3 = rand2D(vec2(integer_x, integer_y+1.0));
+      float v4 = rand2D(vec2(integer_x+1.0, integer_y +1.0));
+
+      float i1 = simple_interpolate(v1 , v2 , fractional_x);
+      float i2 = simple_interpolate(v3 , v4 , fractional_x);
+
+      return simple_interpolate(i1 , i2 , fractional_y);
+}
+ 
+float Noise2D(in vec2 coord, in float wavelength)
+{
+return interpolatedNoise2D(coord.x/wavelength, coord.y/wavelength);
+
+}
  
 void main()
 {
@@ -198,7 +231,18 @@ color = sat * color + (1.0 - sat) * mix(color, black, smoothstep(0.4+cthorizon,0
 
 // the terrain below the horizon gets drawn in one optical thickness
 vec3 terrainHazeColor = eqColorFactor * hColor;	
-color = mix(color, terrainHazeColor ,smoothstep(0.01 + ctterrain, 0.0+ctterrain, ct));
+
+// determine a visibility-dependent angle for how smoothly the haze blends over the skydome
+
+float hazeBlendAngle = max(0.01,1000.0/avisibility + 0.3 * (1.0 - smoothstep(5000.0, 30000.0, avisibility)));
+float altFactor = smoothstep(-300.0, 0.0, delta_z);
+float altFactor2 =  0.2 + 0.8 * smoothstep(-3000.0, 0.0, delta_z);
+hazeBlendAngle = hazeBlendAngle + 0.1 * altFactor;
+hazeBlendAngle = hazeBlendAngle +  (1.0-horizon_roughness) * altFactor2 * 0.1 *  Noise2D(vec2(0.0,cphi), 0.3);
+
+
+color = mix(color, terrainHazeColor ,smoothstep(hazeBlendAngle + ctterrain, 0.0+ctterrain, ct));
+
 
 // mix fog the skydome with the right amount of haze
 

Shaders/skydome.vert

@@ -18,7 +18,7 @@ varying vec3 mie;
 varying vec3 eye;
 varying vec3 hazeColor;
 varying float ct;
-//varying float cosphi;
+varying float cphi;
 varying float delta_z;
 varying float alt; 
 varying float earthShade;
@@ -252,19 +252,9 @@ void main()
 
     if (terminator > 1000000.0){yprime = -sqrt(2.0 * EarthRadius * hazeLayerAltitude);}
 
-    //float edgeAlt = max(hazeLayerAltitude - (alt-terrain_alt)/avisibility * visibility, terrain_alt);
-    
-    //yprime = yprime -sqrt(2.0 * EarthRadius * edgeAlt);
-
     float terminator_width = 200000.0;
     earthShade = 0.9 * smoothstep((terminator_width+ terminator), (-terminator_width + terminator), yprime) + 0.1;
 
-
-//hazeColor = vec3 (gl_LightSource[0].diffuse.x, gl_LightSource[0].diffuse.y, gl_LightSource[0].diffuse.z);
-
-    //hazeColor.x = hazeColor.x * 0.83;
-    //hazeColor.y = hazeColor.y * 0.9;  
-
      float lightArg = (terminator-yprime)/100000.0;
      vec4 light_diffuse;
      light_diffuse.b = light_func(lightArg, 1.330e-05, 0.264, 2.527, 1.08e-05, 1.0);
@@ -275,18 +265,11 @@ void main()
 
      float intensity = length(hazeColor.xyz);
      float mie_magnitude = 0.5 * smoothstep(350000.0, 150000.0, terminator -sqrt(2.0 * EarthRadius * terrain_alt)); 
+     cphi = dot(normalize(relVector), normalize(lightHorizon));
      float mie_angle = (0.5 *  dot(normalize(relVector), normalize(lightFull)) ) + 0.5;
      hazeColor = intensity * ((1.0 - mie_magnitude) + mie_magnitude * mie_angle) * normalize(mix(hazeColor,  vec3 (0.5, 0.58, 0.65), mie_magnitude * (0.5 - 0.5 * mie_angle)) ); 
 
 
-// high altitude desaturation - would be best here this causes a box-like bug for some reason
-// so it moved to the fragment shader where it has no issues
-
-//float intensity = length(hazeColor.xyz);
-//hazeColor = intensity * normalize (mix(hazeColor, intensity * vec3 (1.0,1.0,1.0), 0.8* smoothstep(5000.0, 50000.0, alt)));
-
-    
-
     // Transform
     gl_Position = gl_ModelViewProjectionMatrix * finalVertex;
 }