Allow bounce easings along a path to return a position outside of the…

… path (#2457)

Don't clamp interpolated distance along path to 'progress' value between 0 and 1.

Bounce in / Bounce out easings can transform the progress to negative values or values higher than 1. `getPosTan` unfortunately clamps the input to be between 0 and 1, so we need to handle the t < 0 and t > 1 cases separately.


This is for the same issue I helped fix in the flutter library as well here: xvrh/lottie-flutter#330

Expected result (both bounce-in and bounce out) along linear and curved paths: 

https://github.com/airbnb/lottie-android/assets/632735/6a25e139-fc81-4c3b-b3f3-be118c56db06

lottie/src/main/java/com/airbnb/lottie/animation/keyframe/PathKeyframeAnimation.java

@@ -11,6 +11,7 @@
 public class PathKeyframeAnimation extends KeyframeAnimation<PointF> {
   private final PointF point = new PointF();
   private final float[] pos = new float[2];
+  private final float[] tangent = new float[2];
   private final PathMeasure pathMeasure = new PathMeasure();
   private PathKeyframe pathMeasureKeyframe;
 
@@ -39,8 +40,23 @@ pathKeyframe.startValue, pathKeyframe.endValue, getLinearCurrentKeyframeProgress
       pathMeasureKeyframe = pathKeyframe;
     }
 
-    pathMeasure.getPosTan(keyframeProgress * pathMeasure.getLength(), pos, null);
-    point.set(pos[0], pos[1]);
+    // allow bounce easings to calculate positions outside the path
+    // by using the tangent at the extremities
+
+    float length = pathMeasure.getLength();
+
+    if (keyframeProgress < 0) {
+      pathMeasure.getPosTan(0, pos, tangent);
+      float tangentAmount = keyframeProgress * length;
+      point.set(pos[0] + tangent[0] * tangentAmount, pos[1] + tangent[1] * tangentAmount);
+    } else if (keyframeProgress > 1) {
+      pathMeasure.getPosTan(length, pos, tangent);
+      float tangentAmount = (keyframeProgress - 1) * length;
+      point.set(pos[0] + tangent[0] * tangentAmount, pos[1] + tangent[1] * tangentAmount);
+    } else {
+      pathMeasure.getPosTan(keyframeProgress * length, pos, null);
+      point.set(pos[0], pos[1]);
+    }
     return point;
   }
 }