ALS model effect accepts a snow flag to let OSM building roofs be snow-covered in winter

Effects/cityLM.eff

@@ -22,6 +22,8 @@
                 <lightmap-factor type="float" n="2">0</lightmap-factor>
                 <lightmap-factor type="float" n="3">0</lightmap-factor>
 
+		<snow-enabled type="int">1</snow-enabled>
+
                 <!--
                 <lightmap-factor type="float" n="3">1</lightmap-factor>
                 <lightmap-color type="vec3d" n="3"> 1 1 1 </lightmap-color>

Effects/model-combined.eff

@@ -104,6 +104,7 @@ please see Docs/README.model-combined.eff for documentation
 		<!-- END Grain texture -->
 		<!-- simulate rain effects -->
 		<rain-enabled type="int">0</rain-enabled>
+		<snow-enabled type="int">0</snow-enabled>
 		<!-- 		Dirt -->
 		<dirt-enabled type="int">0</dirt-enabled>
 		<dirt-multi type="int">0</dirt-multi>
@@ -147,6 +148,8 @@ please see Docs/README.model-combined.eff for documentation
 		<fogtype><use>/sim/rendering/shaders/skydome</use></fogtype>
 		<wetness><use>/environment/surface/wetness</use></wetness>
 		<rnorm><use>/environment/rain-norm</use></rnorm>
+		<snow_level><use>/environment/snow-level-m</use></snow_level>
+    		<snow_thickness_factor><use>/environment/surface/snow-thickness-factor</use></snow_thickness_factor>
 		<cloudpos1_x><use>/local-weather/cloud-shadows/cloudpos-x[0]</use></cloudpos1_x>
 		<cloudpos1_y><use>/local-weather/cloud-shadows/cloudpos-y[0]</use></cloudpos1_y>
 		<cloudpos2_x><use>/local-weather/cloud-shadows/cloudpos-x[1]</use></cloudpos2_x>
@@ -774,7 +777,7 @@ please see Docs/README.model-combined.eff for documentation
 				   </value>
 		  	   </uniform>
 
-			   <!-- simulate wetness and rain-->
+			   <!-- simulate wetness, rain and snow -->
 		  	    <uniform>
 				   <name>rain_enabled</name>
 				   <type>int</type>
@@ -783,6 +786,26 @@ please see Docs/README.model-combined.eff for documentation
 				   </value>
 		  	    </uniform>
 			   
+			    <uniform>
+				   <name>snow_enabled</name>
+				   <type>int</type>
+				   <value>
+			  	   	<use>snow-enabled</use>
+				   </value>
+		  	    </uniform>
+			   
+			   	<uniform>
+        			   <name>snowlevel</name>
+        			   <type>float</type>
+        			   <value><use>snow_level</use></value>
+      			   </uniform>
+
+			   <uniform>
+				   <name>snow_thickness_factor</name>
+				   <type>float</type>
+				   <value><use>snow_thickness_factor</use></value>
+			   </uniform>
+
 			   <!-- set the amount of ambient light correction 0.0 - 1.0  -->
 			   <uniform>
 				   <name>amb_correction</name>

Shaders/model-ALS-ultra.frag

@@ -41,6 +41,7 @@ uniform int cloud_shadow_flag;
 uniform int use_searchlight;
 uniform int use_landing_light;
 uniform int use_alt_landing_light;
+uniform int snow_enabled;
 
 uniform float amb_correction;
 uniform float dirt_b_factor;
@@ -72,6 +73,8 @@ uniform float terminator;
 uniform float terrain_alt;
 uniform float visibility;
 uniform float air_pollution;
+uniform float snowlevel;
+uniform float snow_thickness_factor;
 
 uniform float osg_SimulationTime;
 
@@ -96,6 +99,7 @@ uniform vec3 dirt_g_color;
 uniform vec3 dirt_b_color;
 
 float DotNoise2D(in vec2 coord, in float wavelength, in float fractionalMaxDotSize, in float dot_density);
+float Noise2D(in vec2 coord, in float wavelength);
 float shadow_func (in float x, in float y, in float noise, in float dist);
 float fog_func (in float targ, in float altitude);
 float rayleigh_in_func(in float dist, in float air_pollution, in float avisibility, in float eye_alt, in float vertex_alt);
@@ -191,6 +195,7 @@ void main (void)
 
 	
     float ct = dot(normalize(up), normalize(vertVec));
+    vec3 relPos = (gl_ModelViewMatrixInverse * vec4 (vertVec,0.0)).xyz;		
 
     /// END geometry for light
 
@@ -241,6 +246,31 @@ void main (void)
 
     /// END grain overlay
 
+    /// BEGIN snowcover
+	
+    vec4 snow_texel = vec4 (0.95, 0.95, 0.95, 1.0);
+
+    if (snow_enabled == 1)
+	{
+	float noise_1m = Noise2D(rawpos.xy, 1.0); 
+       	float noise_5m = Noise2D(rawpos.xy, 5.0);
+		
+	float noise_term = 0.5 * (noise_5m - 0.5);
+	noise_term +=  0.5 * (noise_1m - 0.5);		
+	snow_texel.a = snow_texel.a * 0.2+0.8* smoothstep(0.2,0.8, 0.3 +noise_term + 0.5*snow_thickness_factor +0.0001*(relPos.z +eye_alt -snowlevel) );
+
+	snow_texel.a *=  smoothstep(0.5, 0.7,dot(VNormal, up));
+
+		
+	float noise_2000m = 0.0; 
+	float noise_10m = 0.0;
+		
+
+	texel.rgb = mix(texel.rgb, snow_texel.rgb, snow_texel.a* smoothstep(snowlevel, snowlevel+200.0,  1.0 * (relPos.z + eye_alt)+ (noise_2000m + 0.1 * noise_10m -0.55) *400.0));
+	}
+	
+	/// END snowcover
+
     vec3 reflVecN;
 
     ///BEGIN bump
@@ -295,7 +325,7 @@ void main (void)
         {pf1 = pow(nDotHV1, 0.5*gl_FrontMaterial.shininess);}
   
 
-    vec3 relPos = (gl_ModelViewMatrixInverse * vec4 (vertVec,0.0)).xyz;		
+
     if (cloud_shadow_flag == 1) 
 	{
 		float cloud_shadow_factor = shadow_func(relPos.x, relPos.y, 1.0, dist);