学步园

            /// <summary> 
            /// C# GDI+ 绘制圆角实心矩形 
            /// </summary> 
            /// <param name="g">Graphics 对象</param> 
            /// <param name="rectangle">要填充的矩形</param> 
            /// <param name="backColor">填充背景色</param> 
            /// <param name="r">圆角半径</param> 
            public static void FillRoundRectangle(Graphics g, Rectangle rectangle, Color backColor, int r)
            {
                rectangle = new Rectangle(rectangle.X, rectangle.Y, rectangle.Width - 1, rectangle.Height - 1);
                Brush b = new SolidBrush(backColor);
                g.FillPath(b, GetRoundRectangle(rectangle, r));
            }

            /// <summary> 
            /// 根据普通矩形得到圆角矩形的路径 
            /// </summary> 
            /// <param name="rectangle">原始矩形</param> 
            /// <param name="r">半径</param> 
            /// <returns>图形路径</returns> 
            private static GraphicsPath GetRoundRectangle(Rectangle rectangle, int r)
            {
                int l = 2 * r;
                // 把圆角矩形分成八段直线、弧的组合，依次加到路径中 
                GraphicsPath gp = new GraphicsPath();
                gp.AddLine(new Point(rectangle.X + r, rectangle.Y), new Point(rectangle.Right - r, rectangle.Y));
                gp.AddArc(new Rectangle(rectangle.Right - l, rectangle.Y, l, l), 270F, 90F);

                gp.AddLine(new Point(rectangle.Right, rectangle.Y + r), new Point(rectangle.Right, rectangle.Bottom - r));
                gp.AddArc(new Rectangle(rectangle.Right - l, rectangle.Bottom - l, l, l), 0F, 90F);

                gp.AddLine(new Point(rectangle.Right - r, rectangle.Bottom), new Point(rectangle.X + r, rectangle.Bottom));
                gp.AddArc(new Rectangle(rectangle.X, rectangle.Bottom - l, l, l), 90F, 90F);

                gp.AddLine(new Point(rectangle.X, rectangle.Bottom - r), new Point(rectangle.X, rectangle.Y + r));
                gp.AddArc(new Rectangle(rectangle.X, rectangle.Y, l, l), 180F, 90F);
                return gp;
            }