UIRect是UIPanel和UIWidget的基類，研究好前者，才能更方便的研究後兩者，所以我將它做為本系列的第一篇。

（注：本系列討論的NGUI版本為3.10.0）

this.absolute = Mathf.FloorToInt(absolute + 0.5f);
 

this.absolute = Mathf.RoundToInt(absolute);

	/// <summary>
	/// Left side anchor.
	/// </summary>

	public AnchorPoint leftAnchor = new AnchorPoint();

	/// <summary>
	/// Right side anchor.
	/// </summary>

	public AnchorPoint rightAnchor = new AnchorPoint(1f);

	/// <summary>
	/// Bottom side anchor.
	/// </summary>

	public AnchorPoint bottomAnchor = new AnchorPoint();

	/// <summary>
	/// Top side anchor.
	/// </summary>

	public AnchorPoint topAnchor = new AnchorPoint(1f);
 

新建一個widget，把Anchors裡的Type改成Unified或者Advanced，我們就可以自行調節Anchor Point了。Unified和Advanced區別在於，Unified統一指定一個Transform為target，而Advanced可以為左右下上每一個Anchor Point指定一個Transform為target。我們這裡以Unified為例：

	/// <summary>
	/// Anchor this rectangle to the specified transform.
	/// </summary>

	public void SetAnchor (GameObject go,
		float left, int leftOffset,
		float bottom, int bottomOffset,
		float right, int rightOffset,
		float top, int topOffset)
	{
		Transform t = (go != null) ? go.transform : null;

		leftAnchor.target = t;
		rightAnchor.target = t;
		topAnchor.target = t;
		bottomAnchor.target = t;

		leftAnchor.relative = left;
		rightAnchor.relative = right;
		bottomAnchor.relative = bottom;
		topAnchor.relative = top;

		leftAnchor.absolute = leftOffset;
		rightAnchor.absolute = rightOffset;
		bottomAnchor.absolute = bottomOffset;
		topAnchor.absolute = topOffset;

		ResetAnchors();
		UpdateAnchors();
	}

	public enum AnchorUpdate
	{
		OnEnable,
		OnUpdate,
		OnStart,
	}

	/// <summary>
	/// Whether anchors will be recalculated on every update.
	/// </summary>

	public AnchorUpdate updateAnchors = AnchorUpdate.OnUpdate;

	/// <summary>
	/// Ensure that all rect references are set correctly on the anchors.
	/// </summary>

	public void ResetAnchors ()
	{
		mAnchorsCached = true;

		leftAnchor.rect		= (leftAnchor.target)	? leftAnchor.target.GetComponent<UIRect>()	 : null;
		bottomAnchor.rect	= (bottomAnchor.target) ? bottomAnchor.target.GetComponent<UIRect>() : null;
		rightAnchor.rect	= (rightAnchor.target)	? rightAnchor.target.GetComponent<UIRect>()	 : null;
		topAnchor.rect		= (topAnchor.target)	? topAnchor.target.GetComponent<UIRect>()	 : null;

		mCam = NGUITools.FindCameraForLayer(cachedGameObject.layer);

		FindCameraFor(leftAnchor);
		FindCameraFor(bottomAnchor);
		FindCameraFor(rightAnchor);
		FindCameraFor(topAnchor);

		mUpdateAnchors = true;
	}

/// Helper function that returns the distance to the camera's directional vector hitting the panel's plane.

/// Get the sides of the rectangle relative to the specified transform.
/// The order is left, top, right, bottom.

/// Helper function that gets the specified anchor's position relative to the chosen transform.

	/// <summary>
	/// Update anchors.
	/// </summary>

	protected void UpdateAnchorsInternal (int frame)
	{
		mUpdateFrame = frame;
		mUpdateAnchors = false;

		bool anchored = false;

		if (leftAnchor.target)
		{
			anchored = true;
			if (leftAnchor.rect != null && leftAnchor.rect.mUpdateFrame != frame)
				leftAnchor.rect.Update();
		}

		if (bottomAnchor.target)
		{
			anchored = true;
			if (bottomAnchor.rect != null && bottomAnchor.rect.mUpdateFrame != frame)
				bottomAnchor.rect.Update();
		}

		if (rightAnchor.target)
		{
			anchored = true;
			if (rightAnchor.rect != null && rightAnchor.rect.mUpdateFrame != frame)
				rightAnchor.rect.Update();
		}

		if (topAnchor.target)
		{
			anchored = true;
			if (topAnchor.rect != null && topAnchor.rect.mUpdateFrame != frame)
				topAnchor.rect.Update();
		}

		// Update the dimensions using anchors
		if (anchored) OnAnchor();
	}