Merge pull request #9175 from CesiumGS/barycentric-divide-check

Improved degenerate barycentric check

CHANGES.md

@@ -6,6 +6,7 @@
 
 - Removed `Scene.debugShowGlobeDepth`. [#9965](https://github.com/CesiumGS/cesium/pull/9965)
 - Removed `CesiumInspectorViewModel.globeDepth` and `CesiumInspectorViewModel.pickDepth`. [#9965](https://github.com/CesiumGS/cesium/pull/9965)
+- `barycentricCoordinates` returns `undefined` when the input triangle is degenerate. [#9175](https://github.com/CesiumGS/cesium/pull/9175)
 
 ##### Additions :tada:
 

Source/Core/GeometryPipeline.js

@@ -2211,6 +2211,9 @@ function computeTriangleAttributes(
   var p1 = Cartesian3.fromArray(positions, i1 * 3, p1Scratch);
   var p2 = Cartesian3.fromArray(positions, i2 * 3, p2Scratch);
   var coords = barycentricCoordinates(point, p0, p1, p2, barycentricScratch);
+  if (!defined(coords)) {
+    return;
+  }
 
   if (defined(normals)) {
     interpolateAndPackCartesian3(

Source/Core/barycentricCoordinates.js

@@ -18,7 +18,7 @@ var scratchCartesian3 = new Cartesian3();
  * @param {Cartesian2|Cartesian3} p1 The second point of the triangle, corresponding to the barycentric y-axis.
  * @param {Cartesian2|Cartesian3} p2 The third point of the triangle, corresponding to the barycentric z-axis.
  * @param {Cartesian3} [result] The object onto which to store the result.
- * @returns {Cartesian3} The modified result parameter or a new Cartesian3 instance if one was not provided.
+ * @returns {Cartesian3|undefined} The modified result parameter or a new Cartesian3 instance if one was not provided. If the triangle is degenerate the function will return undefined.
  *
  * @example
  * // Returns Cartesian3.UNIT_X
@@ -96,14 +96,13 @@ function barycentricCoordinates(point, p0, p1, p2, result) {
   result.z = dot00 * dot12 - dot01 * dot02;
   var q = dot00 * dot11 - dot01 * dot01;
 
-  // This is done to avoid dividing by infinity causing a NaN
-  if (result.y !== 0) {
-    result.y /= q;
-  }
-  if (result.z !== 0) {
-    result.z /= q;
+  // Triangle is degenerate
+  if (q === 0) {
+    return undefined;
   }
 
+  result.y /= q;
+  result.z /= q;
   result.x = 1.0 - result.y - result.z;
   return result;
 }

Source/Core/pointInsideTriangle.js

@@ -1,7 +1,8 @@
 import barycentricCoordinates from "./barycentricCoordinates.js";
 import Cartesian3 from "./Cartesian3.js";
+import defined from "./defined.js";
 
-var coords = new Cartesian3();
+var scratchBarycentricCoords = new Cartesian3();
 
 /**
  * Determines if a point is inside a triangle.
@@ -23,7 +24,16 @@ var coords = new Cartesian3();
  *   new Cesium.Cartesian2(0.0, 1.0));
  */
 function pointInsideTriangle(point, p0, p1, p2) {
-  barycentricCoordinates(point, p0, p1, p2, coords);
+  var coords = barycentricCoordinates(
+    point,
+    p0,
+    p1,
+    p2,
+    scratchBarycentricCoords
+  );
+  if (!defined(coords)) {
+    return false;
+  }
   return coords.x > 0.0 && coords.y > 0.0 && coords.z > 0;
 }
 export default pointInsideTriangle;

Specs/Core/barycentricCoordinatesSpec.js

@@ -78,14 +78,13 @@ describe("Core/barycentricCoordinates", function () {
     );
   });
 
-  it("evaluates without throwing a NaN", function () {
-    var point = Cartesian3.multiplyByScalar(
-      Cartesian3.add(p1, p1, p1),
-      0.5,
-      new Cartesian3()
-    );
+  it("returns undefined for colinear points", function () {
+    var p0 = new Cartesian3(-1.0, -1.0, 0.0);
+    var p1 = new Cartesian3(0.0, 0.0, 0.0);
+    var p2 = new Cartesian3(1.0, 1.0, 0.0);
+    var point = new Cartesian3(0.5, 0.5, 0.0);
     var coord = barycentricCoordinates(point, p0, p1, p2);
-    expect(coord.z).not.toBeNaN();
+    expect(coord).toBeUndefined();
   });
 
   it("evaluates with equal length sides", function () {