/// <summary>
/// 计算矩形外某个点与矩形中点的连线，与矩形的相交点。
/// </summary>
/// <param name="rect"></param>
/// <param name="outerPoint"></param>
/// <returns></returns>
public static Point CalcCrossPoint(Rect rect, Point outerPoint)
{
//单元测试:
//var res = CalcCrossPoint(new Point(300, 150), new Rect(0, 0, 200, 100));
//if (res != new Point(200, 100)) throw new NotSupportedException();
//res = CalcCrossPoint(new Point(100, 200), new Rect(0, 0, 200, 100));
//if (res != new Point(100, 100)) throw new NotSupportedException();
//res = CalcCrossPoint(new Point(100, -100), new Rect(0, 0, 200, 100));
//if (res != new Point(100, 0)) throw new NotSupportedException();
var area = GetRectArea(rect, outerPoint);
Line line1 = new Line { A = rect.GetCenterPoint(), B = outerPoint };
Line line2 = new Line();
switch (area)
{
case RectLineDirection.Left:
line2.A = rect.TopLeft;
line2.B = rect.BottomLeft;
break;
case RectLineDirection.Top:
line2.A = rect.TopLeft;
line2.B = rect.TopRight;
break;
case RectLineDirection.Right:
line2.A = rect.TopRight;
line2.B = rect.BottomRight;
break;
case RectLineDirection.Bottom:
line2.A = rect.BottomRight;
line2.B = rect.BottomLeft;
break;
default:
break;
}
Point point = CalcCrossPoint(line1, line2);
point.X = Round(point.X);
point.Y = Round(point.Y);
return point;
}
/// <summary>
/// 返回矩形中心点与指定点的向量，与矩形相交的点。
/// 简单地认为，这个点即是矩形边上最靠近指定点的点。
/// </summary>
/// <param name="rect"></param>
/// <param name="point"></param>
/// <returns></returns>
public static Point NearestPointOnLine(Rect rect, Point point)
{
Point res = point;
if (rect.Contains(res))
{
var center = rect.GetCenterPoint();
//没有斜率
if (res.Y == center.Y)
{
if (res.X < center.X)
{
res = RectAlgorithm.GetRectAbsolute(rect, new Point(0, 0.5));
}
else
{
res = RectAlgorithm.GetRectAbsolute(rect, new Point(1, 0.5));
}
return res;
}
else
{
//使用向量继续向该方向延长。
Vector v = new Vector(res.X - center.X, res.Y - center.Y);
v *= 10000;
while (true)
{
res += v;
if (!rect.Contains(res)) break;
}
}
}
res = CalcCrossPoint(rect, point);
return res;
}
/// <summary>
/// 按照中心点与四个角的连线，把空间分为四个区域。
/// 返回点所在的区域。
/// </summary>
/// <param name="rect"></param>
/// <param name="point"></param>
/// <returns></returns>
public static RectLineDirection GetRectArea(Rect rect, Point point)
{
var c = rect.GetCenterPoint();
var fromAngle = AngleFromCenter(c, point);
var tl = AngleFromCenter(c, rect.TopLeft);
var tr = AngleFromCenter(c, rect.TopRight);
var br = AngleFromCenter(c, rect.BottomRight);
var bl = AngleFromCenter(c, rect.BottomLeft);
if (fromAngle > tl && fromAngle <= tr)
{
return RectLineDirection.Top;
}
else if (fromAngle > tr && fromAngle <= br)
{
return RectLineDirection.Right;
}
else if (fromAngle > br && fromAngle <= bl)
{
return RectLineDirection.Bottom;
}
else
{
return RectLineDirection.Left;
}
}