Add shaders

Sources/Shaders/SnowedSpeedTree.cginc

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+	
+	uniform float4    _GS_SnowData1;	// x = relief, y = occlusion, z = glitter, w = brightness
+	uniform float4    _GS_SnowData2;	// x = minimum altitude, y = altitude scattering, z = coverage extension
+    uniform float4    _GS_SnowCamPos;
+    uniform half4     _GS_SnowTint;
+	uniform sampler2D_float _GS_DepthTexture;
+    
+	// get snow coverage on trees
+	void SetTreeCoverage(Input IN, inout SurfaceOutput o) { 
+
+		// prevent snow on sides and below minimum altitude
+		float3 wsNormal = IN.worldNormal; 
+		float ny = wsNormal.y - 0.2;
+		float flatSurface = saturate(ny * 10.0);
+		float minAltitude = saturate( IN.worldPos.y - _GS_SnowData2.x);
+
+          // mask support
+        #if defined(GLOBALSNOW_MASK)
+            float4 st = float4(IN.worldPos.xz - _GS_SnowCamPos.xz, 0, 0);
+            st *= _GS_SnowData2.z;
+            st += 0.5;
+            float zmask = tex2Dlod(_GS_DepthTexture, st).g;
+            float snowCover   = max(minAltitude * flatSurface - zmask, 0);
+        #else
+            float snowCover   = minAltitude * flatSurface;
+        #endif
+		
+		
+		// pass color data to output shader
+		o.Albedo = _GS_SnowData1.www;
+        o.Albedo.rgb *= _GS_SnowTint.rgb;
+		o.Alpha *= snowCover;
+	}