Guard against negative height samples in HeightmapTerrainData

Source/Core/ArcGisImageServerTerrainProvider.js

@@ -60,7 +60,7 @@ define([
      *   proxy : new Cesium.DefaultProxy('/terrain/')
      * });
      * viewer.terrainProvider = terrainProvider;
-     * 
+     *
      *  @see TerrainProvider
      */
     function ArcGisImageServerTerrainProvider(options) {
@@ -91,7 +91,9 @@ define([
             elementsPerHeight : 3,
             stride : 4,
             elementMultiplier : 256.0,
-            isBigEndian : true
+            isBigEndian : true,
+            lowestEncodedHeight : 0,
+            highestEncodedHeight : 256 * 256 * 256
         };
 
         this._errorEvent = new Event();

Source/Core/CesiumTerrainProvider.js

@@ -75,7 +75,7 @@ define([
      *     url : 'https://assets.agi.com/stk-terrain/world',
      *     requestVertexNormals : true
      * });
-     * 
+     *
      * // Terrain geometry near the surface of the globe is difficult to view when using NaturalEarthII imagery,
      * // unless the TerrainProvider provides additional lighting information to shade the terrain (as shown above).
      * var imageryProvider = Cesium.createTileMapServiceImageryProvider({
@@ -91,7 +91,7 @@ define([
      *
      * // The globe must enable lighting to make use of the terrain's vertex normals
      * viewer.scene.globe.enableLighting = true;
-     * 
+     *
      * @see TerrainProvider
      */
     function CesiumTerrainProvider(options) {
@@ -180,7 +180,9 @@ define([
                         elementsPerHeight : 1,
                         stride : 1,
                         elementMultiplier : 256.0,
-                        isBigEndian : false
+                        isBigEndian : false,
+                        lowestEncodedHeight : 0,
+                        highestEncodedHeight : 256 * 256
                     };
                 that._hasWaterMask = true;
                 that._requestWaterMask = true;

Source/Core/HeightmapTerrainData.js

@@ -89,7 +89,7 @@ define([
      *   childTileMask : childTileMask,
      *   waterMask : waterMask
      * });
-     * 
+     *
      * @see TerrainData
      * @see QuantizedMeshTerrainData
      */
@@ -350,6 +350,12 @@ define([
             for (var i = 0; i < width; ++i) {
                 var longitude = CesiumMath.lerp(destinationRectangle.west, destinationRectangle.east, i / (width - 1));
                 var heightSample = interpolateMeshHeight(buffer, encoding, heightOffset, heightScale, skirtHeight, sourceRectangle, width, height, longitude, latitude, exaggeration);
+
+                // Use conditionals here instead of Math.min and Math.max so that an undefined
+                // lowestEncodedHeight or highestEncodedHeight has no effect.
+                heightSample = heightSample < structure.lowestEncodedHeight ? structure.lowestEncodedHeight : heightSample;
+                heightSample = heightSample > structure.highestEncodedHeight ? structure.highestEncodedHeight : heightSample;
+
                 setHeight(heights, elementsPerHeight, elementMultiplier, divisor, stride, isBigEndian, j * width + i, heightSample);
             }
         }
@@ -448,6 +454,7 @@ define([
     }
 
     function interpolateMeshHeight(buffer, encoding, heightOffset, heightScale, skirtHeight, sourceRectangle, width, height, longitude, latitude, exaggeration) {
+        // returns a height encoded according to the structure's heightScale and heightOffset.
         var fromWest = (longitude - sourceRectangle.west) * (width - 1) / (sourceRectangle.east - sourceRectangle.west);
         var fromSouth = (latitude - sourceRectangle.south) * (height - 1) / (sourceRectangle.north - sourceRectangle.south);
 

Source/Core/VRTheWorldTerrainProvider.js

@@ -64,7 +64,7 @@ define([
      *   url : 'https://www.vr-theworld.com/vr-theworld/tiles1.0.0/73/'
      * });
      * viewer.terrainProvider = terrainProvider;
-     * 
+     *
      * @see TerrainProvider
      */
     function VRTheWorldTerrainProvider(options) {
@@ -90,7 +90,9 @@ define([
                 elementsPerHeight : 3,
                 stride : 4,
                 elementMultiplier : 256.0,
-                isBigEndian : true
+                isBigEndian : true,
+                lowestEncodedHeight : 0,
+                highestEncodedHeight : 256 * 256 * 256
             };
 
         var credit = options.credit;

Specs/Core/HeightmapTerrainDataSpec.js

@@ -246,6 +246,29 @@ defineSuite([
                  expect(upsampled._buffer).toEqual([2, 1, 0, 3, 1, 0, 3, 1, 0, 4, 1, 0, 4, 1, 0, 5, 1, 0, 5, 1, 0, 6, 1, 0, 6, 1, 0, 7, 1, 0, 7, 1, 0, 8, 1, 0, 8, 1, 0, 9, 1, 0, 9, 1, 0, 10, 1, 0]);
              });
          });
+
+         it('upsample clamps out of range data', function() {
+             data = new HeightmapTerrainData({
+                 buffer : new Float32Array([-1.0, -2.0, -3.0, -4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0]),
+                 width : 4,
+                 height : 4,
+                 structure : {
+                     stride: 1,
+                     elementsPerHeight: 1,
+                     lowestEncodedHeight : 1,
+                     highestEncodedHeight : 7
+                 }
+             });
+
+             return data.createMesh(tilingScheme, 0, 0, 0, 1).then(function() {
+                 return data.upsample(tilingScheme, 0, 0, 0, 0, 0, 1);
+             }).then(function(upsampled) {
+                 expect(upsampled.wasCreatedByUpsampling()).toBe(true);
+                 expect(upsampled._width).toBe(4);
+                 expect(upsampled._height).toBe(4);
+                 expect(upsampled._buffer).toEqual([1, 1, 1, 1, 2, 1.5, 2, 1.5, 5, 5.5, 6, 6.5, 7, 7, 7, 7]);
+             });
+         });
      });
 
      describe('isChildAvailable', function() {