public void applyTo(OffscreenLayer.ComposeOp op) {
    if (Color.alpha(color) > 0) {
      op.shadow = this;
    } else {
      op.shadow = null;
    }
  }
Applies a shadow to the provided ComposeOp, to be used with OffscreenLayer.
lottie/src/main/java/com/airbnb/lottie/utils/DropShadow.java