Fix polyline color issue involving duplicate positions

CHANGES.md

@@ -9,6 +9,7 @@
 - Fixes an error with removing a CZML datasource when the clock interval has a duration of zero. [#9637](https://github.com/CesiumGS/cesium/pull/9637)
 - Fixed the ability to set a material's image to `undefined` and `Material.DefaultImageId`. [#9644](https://github.com/CesiumGS/cesium/pull/9644)
 - Fixed render crash when creating a `polylineVolume` with very close points. [#9669](https://github.com/CesiumGS/cesium/pull/9669)
+- Fixed a bug in `PolylineGeometry` that incorrectly shifted colors when duplicate positions were removed. [#9676](https://github.com/CesiumGS/cesium/pull/9676)
 
 ### 1.83 - 2021-07-01
 

Source/Core/PolylineGeometry.js

@@ -309,10 +309,35 @@ PolylineGeometry.createGeometry = function (polylineGeometry) {
   var j;
   var k;
 
+  var removedIndices = [];
   var positions = arrayRemoveDuplicates(
     polylineGeometry._positions,
-    Cartesian3.equalsEpsilon
+    Cartesian3.equalsEpsilon,
+    false,
+    removedIndices
   );
+
+  if (defined(colors) && removedIndices.length > 0) {
+    var removedArrayIndex = 0;
+    var nextRemovedIndex = removedIndices[0];
+    colors = colors.filter(function (color, index) {
+      var remove = false;
+      if (colorsPerVertex) {
+        remove =
+          index === nextRemovedIndex || (index === 0 && nextRemovedIndex === 1);
+      } else {
+        remove = index + 1 === nextRemovedIndex;
+      }
+
+      if (remove) {
+        removedArrayIndex++;
+        nextRemovedIndex = removedIndices[removedArrayIndex];
+        return false;
+      }
+      return true;
+    });
+  }
+
   var positionsLength = positions.length;
 
   // A width of a pixel or less is not a valid geometry, but in order to support external data

Source/Core/arrayRemoveDuplicates.js

@@ -10,7 +10,8 @@ var removeDuplicatesEpsilon = CesiumMath.EPSILON10;
  *
  * @param {Array.<*>} [values] The array of values.
  * @param {Function} equalsEpsilon Function to compare values with an epsilon. Boolean equalsEpsilon(left, right, epsilon).
- * @param {Boolean} [wrapAround=false] Compare the last value in the array against the first value.
+ * @param {Boolean} [wrapAround=false] Compare the last value in the array against the first value. If they are equal, the last value is removed.
+ * @param {Array.<Number>} [removedIndices=undefined] Store the indices that correspond to the duplicate items removed from the array, if there were any.
  * @returns {Array.<*>|undefined} A new array of values with no adjacent duplicate values or the input array if no duplicates were found.
  *
  * @example
@@ -33,9 +34,25 @@ var removeDuplicatesEpsilon = CesiumMath.EPSILON10;
  *     new Cesium.Cartesian3(1.0, 1.0, 1.0)];
  * var nonDuplicatevalues = Cesium.PolylinePipeline.removeDuplicates(values, Cartesian3.equalsEpsilon, true);
  *
+ * @example
+ * // Returns [(1.0, 1.0, 1.0), (2.0, 2.0, 2.0), (3.0, 3.0, 3.0)]
+ * // removedIndices will be equal to [1, 3, 5]
+ * var values = [
+ *     new Cesium.Cartesian3(1.0, 1.0, 1.0),
+ *     new Cesium.Cartesian3(1.0, 1.0, 1.0),
+ *     new Cesium.Cartesian3(2.0, 2.0, 2.0),
+ *     new Cesium.Cartesian3(2.0, 2.0, 2.0),
+ *     new Cesium.Cartesian3(3.0, 3.0, 3.0),
+ *     new Cesium.Cartesian3(1.0, 1.0, 1.0)];
+ * var nonDuplicatevalues = Cesium.PolylinePipeline.removeDuplicates(values, Cartesian3.equalsEpsilon, true);
  * @private
  */
-function arrayRemoveDuplicates(values, equalsEpsilon, wrapAround) {
+function arrayRemoveDuplicates(
+  values,
+  equalsEpsilon,
+  wrapAround,
+  removedIndices
+) {
   //>>includeStart('debug', pragmas.debug);
   Check.defined("equalsEpsilon", equalsEpsilon);
   //>>includeEnd('debug');
@@ -45,60 +62,69 @@ function arrayRemoveDuplicates(values, equalsEpsilon, wrapAround) {
   }
 
   wrapAround = defaultValue(wrapAround, false);
+  var storeRemovedIndices = defined(removedIndices);
 
   var length = values.length;
   if (length < 2) {
     return values;
   }
 
   var i;
-  var v0;
+  var v0 = values[0];
   var v1;
 
-  for (i = 1; i < length; ++i) {
-    v0 = values[i - 1];
-    v1 = values[i];
-    if (equalsEpsilon(v0, v1, removeDuplicatesEpsilon)) {
-      break;
-    }
-  }
+  // We only want to create a new array if there are duplicates in the array.
+  // As such, cleanedValues is undefined until it encounters the first duplicate, if it exists.
+  var cleanedValues;
+  var lastCleanIndex = 0;
 
-  if (i === length) {
-    if (
-      wrapAround &&
-      equalsEpsilon(
-        values[0],
-        values[values.length - 1],
-        removeDuplicatesEpsilon
-      )
-    ) {
-      return values.slice(1);
-    }
-    return values;
-  }
+  // removedIndexLCI keeps track of where lastCleanIndex would be if it were sorted into the removedIndices array.
+  // In case of arrays such as [A, B, C, ..., A, A, A], removedIndices will not be sorted properly without this.
+  var removedIndexLCI = -1;
 
-  var cleanedvalues = values.slice(0, i);
-  for (; i < length; ++i) {
-    // v0 is set by either the previous loop, or the previous clean point.
+  for (i = 1; i < length; ++i) {
     v1 = values[i];
-    if (!equalsEpsilon(v0, v1, removeDuplicatesEpsilon)) {
-      cleanedvalues.push(v1);
+    if (equalsEpsilon(v0, v1, removeDuplicatesEpsilon)) {
+      if (!defined(cleanedValues)) {
+        cleanedValues = values.slice(0, i);
+        lastCleanIndex = i - 1;
+        removedIndexLCI = 0;
+      }
+      if (storeRemovedIndices) {
+        removedIndices.push(i);
+      }
+    } else {
+      if (defined(cleanedValues)) {
+        cleanedValues.push(v1);
+        lastCleanIndex = i;
+        if (storeRemovedIndices) {
+          removedIndexLCI = removedIndices.length;
+        }
+      }
       v0 = v1;
     }
   }
 
   if (
     wrapAround &&
-    cleanedvalues.length > 1 &&
-    equalsEpsilon(
-      cleanedvalues[0],
-      cleanedvalues[cleanedvalues.length - 1],
-      removeDuplicatesEpsilon
-    )
+    equalsEpsilon(values[0], values[length - 1], removeDuplicatesEpsilon)
   ) {
-    cleanedvalues.shift();
+    if (storeRemovedIndices) {
+      if (defined(cleanedValues)) {
+        removedIndices.splice(removedIndexLCI, 0, lastCleanIndex);
+      } else {
+        removedIndices.push(length - 1);
+      }
+    }
+
+    if (defined(cleanedValues)) {
+      cleanedValues.length -= 1;
+    } else {
+      cleanedValues = values.slice(0, -1);
+    }
   }
 
-  return cleanedvalues;
+  return defined(cleanedValues) ? cleanedValues : values;
 }
+
 export default arrayRemoveDuplicates;