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Allow bounce easings along a path to return a position outside of the path #2457

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merged 1 commit into from
Jan 31, 2024
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Allow bounce easings along a path to return a position outside of the path #2457

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20 changes: 18 additions & 2 deletions lottie/src/main/java/com/airbnb/lottie/animation/keyframe/PathKeyframeAnimation.java
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Original file line number Diff line number Diff line change
Expand Up @@ -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;

Expand Down Expand Up @@ -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]);
}
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Nit: since getPosTan() already clamps to end points, you could consolidate some calls

float distance =  keyframeProgress * length;
pathMeasure.getPosTan(distance, pos, tangent);
point.set(pos[0], pos[1]);

if (distance < 0) {
  point.offset(tangent[0] * distance, tangent[1] * distance);
} else if (distance > length) {
  point.offset(tangent[0] * (distance - length), tangent[1] * (distance - length));
}

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Thanks @fmalita
@idlewan want to put up another PR for this or would you like me to?

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Sure thing, thanks for proposing a cleaner version!
Here's the PR: #2459

return point;
}
}
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