Fix missing wall segments for some extruded polygons

CHANGES.md

@@ -18,6 +18,7 @@ Change Log
 * Reduces size of approximateTerrainHeights.json by rounding the numbers [#7959](https://github.com/AnalyticalGraphicsInc/cesium/pull/7959)
 * Fixed undefined `quadDetails` error from zooming into the map really close. [#8011](https://github.com/AnalyticalGraphicsInc/cesium/pull/8011)
 * Fixed triangulation bug in polygons using `ArcType.RHUMB`. [#8042](https://github.com/AnalyticalGraphicsInc/cesium/issues/8042)
+* Fixed a bug where extruded polygons would sometimes be missing segments. [#8035](https://github.com/AnalyticalGraphicsInc/cesium/pull/8035)
 
 ### 1.61 - 2019-09-03
 

Source/Core/PolygonGeometryLibrary.js

@@ -579,7 +579,9 @@ define([
         }
 
         length = edgePositions.length;
-        var indices = IndexDatatype.createTypedArray(length / 3, length - positions.length * 6);
+        var vertexCount = length / 3;
+        var indices = IndexDatatype.createTypedArray(vertexCount, vertexCount * 3); // Assuming no vertices drop, each segment takes 6 indices and there are vertexCount / 2 walls
+
         var edgeIndex = 0;
         length /= 6;
 
@@ -603,6 +605,10 @@ define([
             indices[edgeIndex++] = LR;
         }
 
+        if (edgeIndex !== indices.length) {
+            indices = indices.slice(0, edgeIndex);
+        }
+
         return new Geometry({
             attributes : new GeometryAttributes({
                 position : new GeometryAttribute({

Specs/Core/PolygonGeometrySpec.js

@@ -622,6 +622,44 @@ describe('Core/PolygonGeometry', function() {
         expect(p.indices.length).toEqual(numTriangles * 3);
     });
 
+    it('does not include indices for extruded walls that are too small', function() {
+        var positions = Cartesian3.fromDegreesArray([
+            7.757161063097392, 48.568676799636634,
+            7.753968290229146, 48.571796467099077,
+            7.755340073906587, 48.571948854067948,
+            7.756263393414589, 48.571947951609708,
+            7.756894446412183, 48.569396703043992
+        ]);
+
+        var pRhumb = PolygonGeometry.createGeometry(PolygonGeometry.fromPositions({
+            vertexFormat : VertexFormat.POSITION_ONLY,
+            positions : positions,
+            extrudedHeight: 1000,
+            closeTop: false,
+            closeBottom: false,
+            arcType: ArcType.RHUMB
+        }));
+
+        var numVertices = 20;
+        var numTriangles = 12;
+        expect(pRhumb.attributes.position.values.length).toEqual(numVertices * 3);
+        expect(pRhumb.indices.length).toEqual(numTriangles * 3);
+
+        var pGeodesic = PolygonGeometry.createGeometry(PolygonGeometry.fromPositions({
+            vertexFormat : VertexFormat.POSITION_ONLY,
+            positions : positions,
+            extrudedHeight: 1000,
+            closeTop: false,
+            closeBottom: false,
+            arcType: ArcType.GEODESIC
+        }));
+
+        numVertices = 20;
+        numTriangles = 10;
+        expect(pGeodesic.attributes.position.values.length).toEqual(numVertices * 3);
+        expect(pGeodesic.indices.length).toEqual(numTriangles * 3);
+    });
+
     it('computes offset attribute', function() {
         var p = PolygonGeometry.createGeometry(PolygonGeometry.fromPositions({
             vertexFormat : VertexFormat.POSITION_ONLY,