Graphics 绘制圆角矩形

参考： http://www.cnblogs.com/xujh/archive/2007/04/17/717433.html

使用 GraphicsPath -- 指定一系列的 Arc, Line

先补充下 Arc 的用法：

//...
Graphics g = e.Graphics;
int radius = 50;    //圆角半径
Rectangle rectArc = new Rectangle(200, 200, 2*radius, 2*radius);  // 弧度区域

g.DrawRectangle(Pens.Purple, rectArc);  //显示区域边框
g.DrawArc(new Pen(Color.Red, 2), rectArc, 180, 90);  // 绘制弧线
g.DrawArc(Pens.Blue, rectArc, 270, 90);

生成的效果：

由此可以推测出圆角矩形中的弧线与直线的关系：

所以最终代码为：

// 要实现 圆角化的 矩形
Rectangle rect = new Rectangle(180, 180, 200, 160);
int cRadius = 15;  // 圆角半径

// 指定图形路径， 有一系列 直线/曲线 组成
GraphicsPath myPath = new GraphicsPath();
myPath.StartFigure();
myPath.AddArc(new Rectangle(new Point(rect.X, rect.Y), new Size(2 * cRadius, 2 * cRadius)), 180, 90);
myPath.AddLine(new Point(rect.X + cRadius, rect.Y), new Point(rect.Right - cRadius, rect.Y));
myPath.AddArc(new Rectangle(new Point(rect.Right - 2 * cRadius, rect.Y), new Size(2 * cRadius, 2 * cRadius)), 270, 90);
myPath.AddLine(new Point(rect.Right, rect.Y + cRadius), new Point(rect.Right, rect.Bottom - cRadius));
myPath.AddArc(new Rectangle(new Point(rect.Right - 2 * cRadius, rect.Bottom - 2 * cRadius), new Size(2 * cRadius, 2 * cRadius)), 0, 90);
myPath.AddLine(new Point(rect.Right - cRadius, rect.Bottom), new Point(rect.X + cRadius, rect.Bottom));
myPath.AddArc(new Rectangle(new Point(rect.X, rect.Bottom - 2 * cRadius), new Size(2 * cRadius, 2 * cRadius)), 90, 90);
myPath.AddLine(new Point(rect.X, rect.Bottom - cRadius), new Point(rect.X, rect.Y + cRadius));
myPath.CloseFigure();
g.DrawPath(new Pen(Color.Red, 1), myPath);