Only compute distance to tile once. Tweak frame state.

Source/Renderer/UniformState.js

@@ -912,7 +912,7 @@ define([
         this._entireFrustum.y = camera.frustum.far;
         this.updateFrustum(camera.frustum);
 
-        this._fogDensity = frameState.fogDensity;
+        this._fogDensity = frameState.fog.density;
 
         this._frameState = frameState;
         this._temeToPseudoFixed = Transforms.computeTemeToPseudoFixedMatrix(frameState.time, this._temeToPseudoFixed);

Source/Scene/FrameState.js

@@ -136,9 +136,11 @@ define([
          */
         this.scene3DOnly = false;
 
-        this.fogEnabled = true;
-        this.fogDensity = undefined;
-        this.fogSSE = undefined;
+        this.fog = {
+            enabled : true,
+            density : undefined,
+            sse : undefined
+        };
     };
 
     /**

Source/Scene/GlobeSurfaceTileProvider.js

@@ -440,9 +440,11 @@ define([
      * @returns {Visibility} The visibility of the tile.
      */
     GlobeSurfaceTileProvider.prototype.computeTileVisibility = function(tile, frameState, occluders) {
-        if (frameState.fogEnabled) {
-            var distance = this.computeDistanceToTile(tile, frameState);
-            if (CesiumMath.fog(distance, frameState.fogDensity) >= 1.0) {
+        var distance = this.computeDistanceToTile(tile, frameState);
+        tile._distance = distance;
+
+        if (frameState.fog.enabled) {
+            if (CesiumMath.fog(distance, frameState.fog.density) >= 1.0) {
                 // Tile is completely in fog so return that it is not visible.
                 return Visibility.NONE;
             }
@@ -938,7 +940,7 @@ define([
         var oceanNormalMap = tileProvider.oceanNormalMap;
         var showOceanWaves = showReflectiveOcean && defined(oceanNormalMap);
         var hasVertexNormals = tileProvider.terrainProvider.ready && tileProvider.terrainProvider.hasVertexNormals;
-        var enableFog = frameState.fogEnabled;
+        var enableFog = frameState.fog.enabled;
 
         if (showReflectiveOcean) {
             --maxTextures;

Source/Scene/QuadtreePrimitive.js

@@ -442,9 +442,7 @@ define([
 
         var maxGeometricError = primitive._tileProvider.getLevelMaximumGeometricError(tile.level);
 
-        var distance = primitive._tileProvider.computeDistanceToTile(tile, frameState);
-        tile._distance = distance;
-
+        var distance = tile._distance;
         var height = frameState.context.drawingBufferHeight;
 
         var camera = frameState.camera;

Source/Scene/Scene.js

@@ -963,6 +963,7 @@ define([
 
     var heightsTable = [659.246, 1275.6501, 2151.1192, 3141.7763, 4777.5198, 6281.2493, 12364.307, 15900.765, 49889.0549, 78026.8259, 99260.7344, 120036.3873, 151011.0158, 156091.1953, 203849.3112, 274866.9803, 319916.3149, 493552.0528, 628733.5874, 1027505.709];
     var densityTable = [2.0e-4, 1.0e-4, 7.0e-5, 5.0e-5, 4.0e-5, 3.0e-5, 1.9e-5, 1.0e-5, 8.5e-6, 6.2e-6, 5.8e-6, 5.3e-6, 5.2e-6, 5.1e-6, 4.2e-6, 4.0e-6, 3.4e-6, 2.6e-6, 2.2e-6, 1.6e-6];
+
     var tableLastIndex = 0;
 
     function findInterval(height) {