如何在 ARCore Sceneform 中旋转节点的旋转动画

据我所知，ARCore 尚不支持步行等 3D 动画，但如何为节点的旋转设置动画？

我知道我可以设置 LocalRotation 或 WorldRotation，但如何以流畅的方式连续制作此动画？

最简单的方法是使用Android 属性动画 https://developer.android.com/guide/topics/graphics/prop-animation。 Sceneform 示例“太阳系”中就是这样做的一个示例。看一眼旋转节点 https://github.com/google-ar/sceneform-android-sdk/blob/master/solarsystem/app/src/main/java/com/google/ar/sceneform/samples/solarsystem/RotatingNode.java。这将使节点绕其轴旋转。

首先，它创建一个对象动画师 https://developer.android.com/reference/android/animation/ObjectAnimator使用 LinearInterpolation 设置围绕圆的 4 个点之间的旋转。

private static ObjectAnimator createAnimator() {
    // Node's setLocalRotation method accepts Quaternions as parameters.
    // First, set up orientations that will animate a circle.
    Quaternion orientation1 = Quaternion.axisAngle(new Vector3(0.0f, 1.0f, 0.0f), 0);
    Quaternion orientation2 = Quaternion.axisAngle(new Vector3(0.0f, 1.0f, 0.0f), 120);
    Quaternion orientation3 = Quaternion.axisAngle(new Vector3(0.0f, 1.0f, 0.0f), 240);
    Quaternion orientation4 = Quaternion.axisAngle(new Vector3(0.0f, 1.0f, 0.0f), 360);

    ObjectAnimator orbitAnimation = new ObjectAnimator();
    orbitAnimation.setObjectValues(orientation1, orientation2, orientation3, orientation4);

    // Next, give it the localRotation property.
    orbitAnimation.setPropertyName("localRotation");

    // Use Sceneform's QuaternionEvaluator.
    orbitAnimation.setEvaluator(new QuaternionEvaluator());

    //  Allow orbitAnimation to repeat forever
    orbitAnimation.setRepeatCount(ObjectAnimator.INFINITE);
    orbitAnimation.setRepeatMode(ObjectAnimator.RESTART);
    orbitAnimation.setInterpolator(new LinearInterpolator());
    orbitAnimation.setAutoCancel(true);

    return orbitAnimation;
  }

接下来，它开始动画：

  orbitAnimation = createAnimator();
  orbitAnimation.setTarget(this);
  orbitAnimation.setDuration(getAnimationDuration());
  orbitAnimation.start();