UGUI——RectMask2D

my notion note

A 2D rectangular mask that allows for clipping / masking of areas outside the mask.

The RectMask2D behaves in a similar way to a standard Mask component. It differs though in some of the restrictions that it has.

A RectMask2D:

Only works in the 2D plane

Requires elements on the mask to be coplanar.

Does not require stencil buffer / extra draw calls

Requires fewer draw calls

Culls elements that are outside the mask area.

stay OnEnable Register yourself in ClipperRegistry,ClipperRegistry Will be in layout After calculation ,Graphic Call before updating cull Perform the culling operation

protected override void OnEnable()
 {
     base.OnEnable();
     m_ShouldRecalculateClipRects = true;
     ClipperRegistry.Register(this);
     MaskUtilities.Notify2DMaskStateChanged(this);
 }

//ClipperRegistry.cs
The clipping is called after layout, but before Graphic update.
public void Cull()
{
   for (var i = 0; i < m_Clippers.Count; ++i)
   {
       m_Clippers[i].PerformClipping();
   }
}

//CanvasUpdateRegistry.cs
 In the constructor PerformUpdate Sign up to willRenderCanvases  Entrustment 
protected CanvasUpdateRegistry()
{
    Canvas.willRenderCanvases += PerformUpdate;
}
        
 private void PerformUpdate()
 {
 	// Handle layoutout Of rebuild
     ..........

     // now layout is complete do culling...
     ClipperRegistry.instance.Cull();

   //  Handle Graphic Of rebuild
   ............
 }

MaskUtilities.Notify2DMaskStateChanged(this);

1. Get all the components in the child node
2. exclude null Same with make One gameobject The components of
3. call IClippable Component's RecalculateClipping Interface
4. MaskableGraphic Rewrote UpdateClipParent Interface
   1. find IClippable In the parent node RectMask2D Components
   2. From the old record RectMask2D Remove itself from the component
   3. call RectMask2D Of AddClippable Interface （ If IClippable yes MaskableGraphic, take IClippable Join in m_MaskableTargets, Otherwise, join m_ClipTargets）
   4. to update m_ParentMask For the new RectMask2D

PerformClipping

1. according to m_ShouldRecalculateClipRects Get the same canvas Next , All under the same parent node RectMask2D（ Get rid of canvas Of sortingorder Set RectMask2D） Here's the picture , Oval yellow RectMask2D Is the current node , All yellow RectMask2D Will be added to the list m_Clippers

   

2. FindCullAndClipWorldRect Calculate all m_Clippers The smallest area of intersection

3. Traverse m_ClipTargets, call SetClipRect

4. Traverse m_MaskableTargets, call SetClipRect（canvasRenderer.EnableRectClipping） and cull IXX Interface , It is used to obtain such components .

SetClipRect by canvasRenderer Turn on （EnableRectClipping(clipRect)） Or turn off rectangle clipping （DisableRectClipping）.

/// <summary>
/// See IClippable.SetClipRect
/// </summary>
public virtual void SetClipRect(Rect clipRect, bool validRect)
{
    if (validRect)
        canvasRenderer.EnableRectClipping(clipRect);
    else
        canvasRenderer.DisableRectClipping();
}