RectMask2D源码解析

public virtual void PerformClipping()
{
    // if the parents are changed
    // or something similar we
    // do a recalculate here
    if (m_ShouldRecalculateClipRects)
    {
      	//获取所有RectMask2D相关节点组件，赋值给out参数 m_Clippers
        MaskUtilities.GetRectMasksForClip(this, m_Clippers); 
        m_ShouldRecalculateClipRects = false;
    }

    // get the compound rects from
    // the clippers that are valid
    bool validRect = true;
    //从根节点开始遍历子节点，计算出所有Mask重叠的部分
    Rect clipRect = Clipping.FindCullAndClipWorldRect(m_Clippers, out validRect);
    if (clipRect != m_LastClipRectCanvasSpace)
    {
        for (int i = 0; i < m_ClipTargets.Count; ++i)
        //去canvasRenderer类去处理两个四边形的相交点，再组合成裁切后的内容
            m_ClipTargets[i].SetClipRect(clipRect, validRect);

        m_LastClipRectCanvasSpace = clipRect;
        m_LastClipRectValid = validRect;
    }
    //对每个UI元素进行剔除操作，依据是上面计算出来的 clipRect
    for (int i = 0; i < m_ClipTargets.Count; ++i)
        m_ClipTargets[i].Cull(m_LastClipRectCanvasSpace, m_LastClipRectValid);
}


public virtual void SetClipRect(Rect clipRect, bool validRect)
{
    if (validRect)
        canvasRenderer.EnableRectClipping(clipRect);
    else
        canvasRenderer.DisableRectClipping();
}