C# winForm GDI+ 在矩形内绘制居中文本并时文本根据矩形大小进行缩放（转载自：http://www.it1352.com/20879.html）

using System.Drawing;

获取缩放后字体大小，函数：

        private Font FindFont(Graphics g, string longString, Size Rec, Font PreferedFont)//画布，文本，矩形，字体
        {//获得缩放后字体
            SizeF RealSize = g.MeasureString(longString, PreferedFont);//文本大小
            float HeightScaleRatio = Rec.Height / RealSize.Height;//高度缩放比例
            float WidthScaleRatio = Rec.Width / RealSize.Width;//宽度缩放比例
            float ScaleRatio = (HeightScaleRatio < WidthScaleRatio) ? ScaleRatio = HeightScaleRatio : ScaleRatio = WidthScaleRatio;//按高度缩放||按宽度缩放
            float ScaleFontSize = PreferedFont.Size * ScaleRatio;//缩放后的字体大小
            return new Font(PreferedFont.FontFamily, ScaleFontSize);
        }

调用（在pictureBox的Paint事件中）：

        private void PictureBox1_Paint(object sender, PaintEventArgs e)
        {
            Graphics g = e.Graphics;//画布
            Pen pen = new Pen(Color.Black) { Width = 0.2F };//画笔
            Font font = new Font("微软雅黑", 12);//字体
            Brush brush = new SolidBrush(Color.Black);//笔刷
            StringFormat strFormat = new StringFormat();//文本格式
            strFormat.LineAlignment = StringAlignment.Center;//垂直居中
            strFormat.Alignment = StringAlignment.Center;//水平居中
            g.TextRenderingHint = System.Drawing.Text.TextRenderingHint.ClearTypeGridFit;//抗锯齿

            Rectangle recHead = new Rectangle(10, 10, PictureBox1.Width-20, PictureBox1.Height-20);//矩形
            g.DrawRectangle(pen, recHead);//绘制矩形
            //文字内容
            Font goodFont = FindFont(g, info[0], recHead.Size, font);//缩放后字体
            g.DrawString("这是一段很长的文本", goodFont, brush, recHead, strFormat);//绘制文本(文本，字体，笔刷，矩形，文本格式)
        }

        private void PictureBox1_Resize(object sender, EventArgs e)
        {
            PictureBox1.Refresh();//初始化，清空之前的绘图
        }