De-dupe gradient stops

lottie/src/main/java/com/airbnb/lottie/parser/GradientColorParser.java

@@ -142,14 +142,12 @@ private GradientColor addOpacityStopsToGradientIfNeeded(GradientColor gradientCo
       }
     }
 
-    int newColorPoints = colorPoints + opacityStops;
-    float[] newPositions = new float[newColorPoints];
+    // Pre-SKIA (Oreo) devices render artifacts when there is two stops in the same position.
+    // As a result, we have to de-dupe the merge color and opacity stop positions.
+    float[] newPositions = mergeUniqueElements(gradientColor.getPositions(), opacityStopPositions);
+    int newColorPoints = newPositions.length;
     int[] newColors = new int[newColorPoints];
 
-    System.arraycopy(gradientColor.getPositions(), 0, newPositions, 0, colorPoints);
-    System.arraycopy(opacityStopPositions, 0, newPositions, colorPoints, opacityStops);
-    Arrays.sort(newPositions);
-
     for (int i = 0; i < newColorPoints; i++) {
       float position = newPositions[i];
       int colorStopIndex = Arrays.binarySearch(colorStopPositions, position);
@@ -223,4 +221,60 @@ private int getColorInBetweenOpacityStops(float position, int color, float[] opa
     }
     throw new IllegalArgumentException("Unreachable code.");
   }
+
+  /**
+   * Takes two sorted float arrays and merges their elements while removing duplicates.
+   */
+  protected static float[] mergeUniqueElements(float[] arrayA, float[] arrayB) {
+    if (arrayA.length == 0) {
+      return arrayB;
+    } else if (arrayB.length == 0) {
+      return arrayA;
+    }
+
+    int aIndex = 0;
+    int bIndex = 0;
+    int mergedIndex = 0;
+    int numDuplicates = 0;
+    // This will be the merged list but may be longer than what is needed if there are duplicates.
+    // If there are, the 0 elements at the end need to be truncated.
+    float[] mergedNotTruncated = new float[arrayA.length + arrayB.length];
+    for (int i = 0; i < mergedNotTruncated.length; i++) {
+      final float a;
+      if (aIndex < arrayA.length) {
+        a = arrayA[aIndex];
+      } else {
+        a = Float.NaN;
+      }
+
+      final float b;
+      if (bIndex < arrayB.length) {
+        b = arrayB[bIndex];
+      } else {
+        b = Float.NaN;
+      }
+
+      if (Float.isNaN(b) || a < b) {
+        mergedNotTruncated[mergedIndex++] = a;
+        aIndex++;
+      } else if (Float.isNaN(a) || b < a) {
+        mergedNotTruncated[mergedIndex++] = b;
+        bIndex++;
+      } else {
+        mergedNotTruncated[mergedIndex++] = a;
+        aIndex++;
+        bIndex++;
+        numDuplicates++;
+      }
+    }
+
+    if (numDuplicates == 0) {
+      return mergedNotTruncated;
+    }
+
+
+    float[] merged = new float[mergedNotTruncated.length - numDuplicates];
+    System.arraycopy(mergedNotTruncated, 0, merged, 0, merged.length);
+    return merged;
+  }
 }

lottie/src/test/java/com/airbnb/lottie/parser/GradientColorParserTest.java

@@ -0,0 +1,4 @@
+import static org.junit.Assert.*;
+public class GradientColorParserTest {
+
+}