Enhance tile skirts light occlusion

CHANGES.md

@@ -35,6 +35,7 @@
 - Implemented sharper rendering and lighting on voxels with CYLINDER and ELLIPSOID shape. [#11875](https://github.com/CesiumGS/cesium/pull/11875)
 - Implemented vertical exaggeration for voxels with BOX shape. [#11887](https://github.com/CesiumGS/cesium/pull/11887)
 - Added the `Check` object of validators to the public api and types. [#11901](https://github.com/CesiumGS/cesium/pull/11901)
+- Added an optional property 'extendedSkirts' to `CesiumTerrainProvider`to enable extended skirts on tiles, improving light occlusion when shadows are enabled. [#11459][https://github.com/cesiumgs/cesium/issues/11459]
 
 ##### Fixes :wrench:
 

packages/engine/Source/Core/CesiumTerrainProvider.js

@@ -45,6 +45,7 @@ function LayerInformation(layer) {
  * @property {boolean} [requestVertexNormals=false] Flag that indicates if the client should request additional lighting information from the server, in the form of per vertex normals if available.
  * @property {boolean} [requestWaterMask=false] Flag that indicates if the client should request per tile water masks from the server, if available.
  * @property {boolean} [requestMetadata=true] Flag that indicates if the client should request per tile metadata from the server, if available.
+ * @property {boolean} [extendedSkirts=false] Flag that indicates if the tile should have extended skirts for better light occlusion when shadows are enabled.
  * @property {Ellipsoid} [ellipsoid] The ellipsoid.  If not specified, the WGS84 ellipsoid is used.
  * @property {Credit|string} [credit] A credit for the data source, which is displayed on the canvas.
  */
@@ -503,6 +504,15 @@ function CesiumTerrainProvider(options) {
    */
   this._requestWaterMask = defaultValue(options.requestWaterMask, false);
 
+  /**
+   * Boolean flag that indicates if the tile should have extended skirts for better light occlusion
+   * when shadows are enabled.
+   * @type {boolean}
+   * @default false
+   * @private
+   */
+  this._extendedSkirts = defaultValue(options.extendedSkirts, false);
+
   /**
    * Boolean flag that indicates if the client should request tile metadata from the server.
    * @type {boolean}
@@ -834,6 +844,7 @@ function createQuantizedMeshTerrainData(provider, buffer, level, x, y, layer) {
     childTileMask: provider.availability.computeChildMaskForTile(level, x, y),
     waterMask: waterMaskBuffer,
     credits: provider._tileCredits,
+    extendedSkirts: provider._extendedSkirts,
   });
 }
 
@@ -1140,6 +1151,19 @@ Object.defineProperties(CesiumTerrainProvider.prototype, {
       return this._availability;
     },
   },
+
+  /**
+   * Gets a value indicating whether or not the requested tiles include extended skirts.
+   * Extended skirts are used for better light occlusion when shadows are enabled.
+   * @memberof CesiumTerrainProvider.prototype
+   * @type {boolean}
+   * @readonly
+   */
+  extendedSkirts: {
+    get: function () {
+      return this._extendedSkirts;
+    },
+  },
 });
 
 /**

packages/engine/Source/Core/QuantizedMeshTerrainData.js

@@ -59,6 +59,7 @@ import TerrainMesh from "./TerrainMesh.js";
  * @param {Uint8Array} [options.encodedNormals] The buffer containing per vertex normals, encoded using 'oct' encoding
  * @param {Uint8Array} [options.waterMask] The buffer containing the watermask.
  * @param {Credit[]} [options.credits] Array of credits for this tile.
+ * @param {boolean} [options.extendedSkirts=false] True if the tile has extended skirts for better light occlusion when shadows are enabled.
  *
  *
  * @example
@@ -203,6 +204,7 @@ function QuantizedMeshTerrainData(options) {
 
   this._createdByUpsampling = defaultValue(options.createdByUpsampling, false);
   this._waterMask = options.waterMask;
+  this._extendedSkirts = defaultValue(options.extendedSkirts, false);
 
   this._mesh = undefined;
 }
@@ -335,6 +337,8 @@ QuantizedMeshTerrainData.prototype.createMesh = function (options) {
     ellipsoid: ellipsoid,
     exaggeration: exaggeration,
     exaggerationRelativeHeight: exaggerationRelativeHeight,
+    level: level,
+    extendedSkirts: this._extendedSkirts,
   });
 
   if (!defined(verticesPromise)) {
@@ -518,6 +522,7 @@ QuantizedMeshTerrainData.prototype.upsample = function (
     ? this._northSkirtHeight
     : shortestSkirt * 0.5;
   const credits = this._credits;
+  const extendedSkirts = this._extendedSkirts;
 
   return Promise.resolve(upsamplePromise).then(function (result) {
     const quantizedVertices = new Uint16Array(result.vertices);
@@ -552,6 +557,7 @@ QuantizedMeshTerrainData.prototype.upsample = function (
       childTileMask: 0,
       credits: credits,
       createdByUpsampling: true,
+      extendedSkirts: extendedSkirts,
     });
   });
 };

packages/engine/Source/Core/TerrainProvider.js

@@ -269,7 +269,31 @@ TerrainProvider.addSkirtIndices = function (
     offset
   );
   vertexIndex += eastIndicesNorthToSouth.length;
-  addSkirtIndices(northIndicesWestToEast, vertexIndex, indices, offset);
+  offset = addSkirtIndices(
+    northIndicesWestToEast,
+    vertexIndex,
+    indices,
+    offset
+  );
+  return offset;
+};
+
+TerrainProvider.addSkirtsBottomPlane = function (
+  WSVertexIndex,
+  WNVertexIndex,
+  ENVertexIndex,
+  ESVertexIndex,
+  indices,
+  offset
+) {
+  // add triangles for bottom plane
+  indices[offset++] = WSVertexIndex;
+  indices[offset++] = WNVertexIndex;
+  indices[offset++] = ENVertexIndex;
+
+  indices[offset++] = WSVertexIndex;
+  indices[offset++] = ENVertexIndex;
+  indices[offset++] = ESVertexIndex;
 };
 
 function getEdgeIndices(width, height) {

packages/engine/Source/Core/createWorldTerrainAsync.js

@@ -9,6 +9,7 @@ import defaultValue from "./defaultValue.js";
  * @param {Object} [options] Object with the following properties:
  * @param {Boolean} [options.requestVertexNormals=false] Flag that indicates if the client should request additional lighting information from the server if available.
  * @param {Boolean} [options.requestWaterMask=false] Flag that indicates if the client should request per tile water masks from the server if available.
+ * @param {Boolean} [options.extendedSkirts=false] Flag that indicates if the tiles should have extended skirts for better light occlusion when shadows are enabled.
  * @returns {Promise<CesiumTerrainProvider>} A promise that resolves to the created CesiumTerrainProvider
  *
  * @see Ion
@@ -43,6 +44,7 @@ function createWorldTerrainAsync(options) {
   return CesiumTerrainProvider.fromIonAssetId(1, {
     requestVertexNormals: defaultValue(options.requestVertexNormals, false),
     requestWaterMask: defaultValue(options.requestWaterMask, false),
+    extendedSkirts: defaultValue(options.extendedSkirts, false),
   });
 }
 export default createWorldTerrainAsync;

packages/engine/Source/Scene/GlobeSurfaceTile.js

@@ -168,7 +168,22 @@ GlobeSurfaceTile.prototype.pick = function (
   const vertices = mesh.vertices;
   const indices = mesh.indices;
   const encoding = mesh.encoding;
-  const indicesLength = indices.length;
+  let indicesLength = indices.length;
+
+  // do not consider skirts pixels for finding terrain interceptions
+  const edgeVertexCount =
+    mesh.westIndicesSouthToNorth.length +
+    mesh.eastIndicesNorthToSouth.length +
+    mesh.southIndicesEastToWest.length +
+    mesh.northIndicesWestToEast.length;
+  const edgeTriangleCount = Math.max(0, (edgeVertexCount - 4) * 2);
+  let skirtsIndexBufferLength = edgeTriangleCount * 3;
+  if (this.level >= 3) {
+    // 2 more triangles for bottom skirts plane
+    skirtsIndexBufferLength += 2 * 3;
+  }
+
+  indicesLength -= skirtsIndexBufferLength;
 
   let minT = Number.MAX_VALUE;
 

packages/engine/Source/Scene/Terrain.js

@@ -115,6 +115,7 @@ Object.defineProperties(Terrain.prototype, {
  * @param {Object} [options] Object with the following properties:
  * @param {Boolean} [options.requestVertexNormals=false] Flag that indicates if the client should request additional lighting information from the server if available.
  * @param {Boolean} [options.requestWaterMask=false] Flag that indicates if the client should request per tile water masks from the server if available.
+ * @param {Boolean} [options.extendedSkirts=false] Flag that indicates if the tiles should have extended skirts for better light occlusion when shadows are enabled.
  * @returns {Terrain} An asynchronous helper object for a CesiumTerrainProvider
  *
  * @see Ion