在Unity中，PlayableBehaviour如何获取片段的开始和结束时间？

在Unity的timeline相关自定义代码编写中，有时候会需要在PlayableBehaviour中获取TimeClip的开始和结束时间，通过PlayableBehaviour提供的接口我们会发现找不到对应的属性或者方法。

这篇回答中有详细解释：How to access the clip timing (start, end time) in PlayableBehaviour functions

这里附代码实现方式，需要在Track、Asset和Playable通过三次传递：

[TrackClipType(typeof(XXXControlAsset))]
public class XXXControlTrack : TrackAsset
{
    public override Playable CreateTrackMixer(PlayableGraph graph, GameObject go, int inputCount)
    {
        foreach (var clip in GetClips())
        {
            var customClip = clip.asset as H2StoryControlAsset;
            if (customClip != null)
            {
                customClip.m_CustomClipStart = clip.start;
                customClip.m_CustomClipEnd = clip.end;
            }
        }
        
        return ScriptPlayable.Create (graph, inputCount);
    }
}

public class XXXControlAsset : PlayableAsset
{
	[HideInInspector]
	public double m_CustomClipStart;
	
	[HideInInspector]
	public double m_CustomClipEnd;
	
	public override Playable CreatePlayable(PlayableGraph graph, GameObject owner)
	{
	    XXXPlayable template = new XXXPlayable()
	    {
	        m_CustomClipStart = m_CustomClipStart,
	        m_CustomClipEnd = m_CustomClipEnd,
	    };
	    
	    return ScriptPlayable.Create(graph, template);
	}
}

public class XXXPlayable : PlayableBehaviour
{
	public double m_CustomClipStart;
	public double m_CustomClipEnd;
	
	//这样可以在PlayableBehaviour中获取对应开始和结束时间
}