NGUI 源码分析- AnchorPoint

AnchorPoint 是 UIRect 的一个内部类，此处规定作为基准的那个对象称为锚点对象，基准对象对应的矩形框称为目标框，当前对象对应的矩形框称为源框。

public class AnchorPoint  
{
    public Transform target;        // 锚点对象
    public float relative = 0f;     // 相对位置：用来确定是相对于目标框的哪个点，0、0.5、1分别对应目标框的下中上或者是左中右点。
    public int absolute = 0;        // 距离，是个整数：源点与目标点的距离（例如AnchorPoint是topAnchor，那么就是两点在y轴方向上的距离）。

    [System.NonSerialized]          // 不允许序列化 也不显示在检视器中。// 关于序列化可以参考 Vector3 中的使用
    public UIRect rect;             // 锚点对象的 rect

    [System.NonSerialized]
    public Camera targetCam;        // 锚点对象的Camera

    public AnchorPoint() { }
    public AnchorPoint(float relative) { this.relative = relative; }

    /// <summary>
    /// Convenience function that sets the anchor's values.
    /// </summary>

    public void Set(float relative, float absolute)
    {
        this.relative = relative;
        this.absolute = Mathf.FloorToInt(absolute + 0.5f); // 看起来是四舍五入
    }

    /// <summary>
    /// Convenience function that sets the anchor's values.
    /// </summary>

    public void Set(Transform target, float relative, float absolute)
    {
        this.target = target;
        this.relative = relative;
        this.absolute = Mathf.FloorToInt(absolute + 0.5f);
    }

    /// <summary>
    /// Set the anchor's value to the nearest of the 3 possible choices of (left, center, right) or (bottom, center, top).
    /// 传入源点到三个可能目标点的距离，将最近的点作为目标点。要按左中右或者下中上的顺序依次输入。
    /// </summary>

    public void SetToNearest(float abs0, float abs1, float abs2) { SetToNearest(0f, 0.5f, 1f, abs0, abs1, abs2); }

    /// <summary>
    /// Set the anchor's value given the 3 possible anchor combinations. Chooses the one with the smallest absolute offset.
    /// </summary>

    public void SetToNearest(float rel0, float rel1, float rel2, float abs0, float abs1, float abs2)
    {
        float a0 = Mathf.Abs(abs0);
        float a1 = Mathf.Abs(abs1);
        float a2 = Mathf.Abs(abs2);

        if (a0 < a1 && a0 < a2) Set(rel0, abs0);
        else if (a1 < a0 && a1 < a2) Set(rel1, abs1);
        else Set(rel2, abs2);
    }

    /// <summary>
    /// Set the anchor's absolute coordinate relative to the specified parent, keeping the relative setting intact.
    /// 目标点不变的情况下设置源点和目标点的距离，相当于是个更新距离的操作。
    /// </summary>

    public void SetHorizontal(Transform parent, float localPos)
    {
        if (rect)
        {
            Vector3[] sides = rect.GetSides(parent); // 获取成相对坐标下的边
            float targetPos = Mathf.Lerp(sides[0].x, sides[2].x, relative);
            absolute = Mathf.FloorToInt(localPos - targetPos + 0.5f); 
        }
        else
        {
            Vector3 targetPos = target.position;
            if (parent != null) targetPos = parent.InverseTransformPoint(targetPos);
            absolute = Mathf.FloorToInt(localPos - targetPos.x + 0.5f);
        }
    }

    /// <summary>
    /// Set the anchor's absolute coordinate relative to the specified parent, keeping the relative setting intact.
    /// </summary>

    public void SetVertical(Transform parent, float localPos)
    {
        if (rect)
        {
            Vector3[] sides = rect.GetSides(parent);
            float targetPos = Mathf.Lerp(sides[3].y, sides[1].y, relative);
            absolute = Mathf.FloorToInt(localPos - targetPos + 0.5f);
        }
        else
        {
            Vector3 targetPos = target.position;
            if (parent != null) targetPos = parent.InverseTransformPoint(targetPos);
            absolute = Mathf.FloorToInt(localPos - targetPos.y + 0.5f);
        }
    }

    /// <summary>
    /// Convenience function that returns the sides the anchored point is anchored to.
    /// 获取目标框的四条边
    /// </summary>

    public Vector3[] GetSides(Transform relativeTo)
    {
        if (target != null)
        {
            if (rect != null) return rect.GetSides(relativeTo);
#if UNITY_4_3 || UNITY_4_5 || UNITY_4_6
			if (target.camera != null) return target.camera.GetSides(relativeTo);
#else
            if (target.GetComponent<Camera>() != null) return target.GetComponent<Camera>().GetSides(relativeTo);
#endif
        }
        return null;
    }
}