作者： Next

动画实现的基础是基类Animation，所有的动画都必须派生于它去实现必要的方法。让我们以一个例子来看看：

import XrFrame from 'XrFrame';
const xrFrameSystem = wx.getXrFrameSystem();

// 定制动画接受的初始化数据接口
interface IXrTeamCameraAnimtionData {
  targets: {
    hikari: XrFrame.Vector3;
    roam: XrFrame.Vector3;
    xinyi: XrFrame.Vector3;
    final: XrFrame.Vector3;
  },
}

// 定制动画接受的播放额外配置接口
interface IXrTeamCameraAnimationOptions {

}

// 定制动画的实现
class XrTeamCameraAnimation extends xrFrameSystem.Animation<
  IXrTeamCameraAnimtionData,
  IXrTeamCameraAnimationOptions
> {
  private _camera: XrFrame.Transform | undefined;
  private _target: XrFrame.Transform | undefined;
  private _targets: IXrTeamCameraAnimtionData['targets'] | undefined;
  private _startC: XrFrame.Vector3 = new xrFrameSystem.Vector3();
  private _endC: XrFrame.Vector3 = new xrFrameSystem.Vector3();
  private _startT: XrFrame.Vector3 = new xrFrameSystem.Vector3();
  private _endT: XrFrame.Vector3 = new xrFrameSystem.Vector3();

  // 动画初始化时会被执行，传入初始数据
  // 必须设置`this.clipNames`，提供给动画组件必要的信息
  public onInit(data: IXrTeamCameraAnimtionData) {
    this._targets = data.targets;
    this.clipNames = ['hikari', 'roam', 'xinyi'];
  }

  // 动画被播放时会被执行，必须返回片段时长`duration`
  // 剩下三个返回参数是可选的，详见API文档
  public onPlay(el: XrFrame.Element, clipName: string, options: IXrTeamCameraAnimationOptions): {
    duration: number,
    loop?: number,
    delay?: number,
    direction?: XrFrame.TDirection
  } {
    this._camera = this._camera || el.getComponent(xrFrameSystem.Transform);
    this._target = el.getComponent(xrFrameSystem.Camera).target;
    this._startT.set(this._target.position);
    this._endT.setValue(this._targets![clipName].x, this._targets![clipName].y, this._targets![clipName].z);
    this._startC.set(this._camera.position);
    this._endC.set(this._endT);
    this._endC.z += 2;

    return {duration: 3};
  }

  // 动画播放进度更新是会被执行，`progress`的范围是`0~1`
  // `el`参数是指这个动画目前作用于哪个元素，因为动画和元素、组件并非总是一一对应的
  public onUpdate(el: XrFrame.Element, progress: number, reverse: boolean) {
    progress = xrFrameSystem.noneParamsEaseFuncs['ease-in-out'](progress);
    this._startT?.lerp(this._endT, progress, this._target?.position);
    this._startC?.lerp(this._endC, progress, this._camera?.position);
  }

  // 动画播放暂停时会被执行，暂停本身的逻辑是自动的
  public onPause(el: XrFrame.Element) {

  }

  // 动画从暂停中唤醒时会被执行
  public onResume(el: XrFrame.Element) {

  }

  // 动画停止时会被执行，包括播放结束和手动停止
  public onStop(el: XrFrame.Element) {

  }
}

这段代码中，我们定制了一个动画，它的几个生命周期来定义其是如何运作的。框架内置了两种动画帧动画和gltf动画，但这里我们先不讨论它们，先看看在实现了一个动画后，如何去创建和操纵它，这也就引入了动画组件。