GDI+在绘制验证码中的使用

GDI+最简单的理解就是用来绘图的。其中包括点、直线、矩形、字符串等等。

先简单来个例子，说明如何在winform窗体中绘制一条直线，并且这条直线不随着窗体的移动而消失。

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace GDIDemo
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            //一根笔 一张纸 两点 绘制直线的对象
        }

        private void button1_Click(object sender, EventArgs e)
        {
            //创建一个GDI对象
            Graphics g = this.CreateGraphics();//new Graphics();
      
            //创建一支画笔对象
            Pen pen = new Pen(Brushes.Yellow);
            
            //创建两个点
            Point p1 = new Point(30, 50);
            Point p2 = new Point(250, 250);

            g.DrawLine(pen, p1, p2);
        }

        /// <summary>
        /// 重新绘制窗体的时候，直线也重新画一遍
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            //创建一个GDI对象
            Graphics g = this.CreateGraphics();//new Graphics();

            //创建一支画笔对象
            Pen pen = new Pen(Brushes.Yellow);

            //创建两个点
            Point p1 = new Point(30, 50);
            Point p2 = new Point(250, 250);

            g.DrawLine(pen, p1, p2);
        }

        private void button2_Click(object sender, EventArgs e)
        {
            Graphics g = this.CreateGraphics();
            Pen pen = new Pen(Brushes.Yellow);
            Size size=new System.Drawing.Size(80,120);
            Rectangle rec = new Rectangle(new Point(50,50),size);
            g.DrawRectangle(pen, rec);
        }
    }
}

那么有了基本的了解就可以用类似的方法来绘制验证码了。主要包括绘制字符串、直线、点三部分，在BitMap位图上面绘制，然后将整个图片镶嵌到PictureBox中，单击该控件爱你，验证码发生变化。具体代码如下

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace 点击生成验证码
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        /// <summary>
        /// 点击更换验证码
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void pictureBox1_Click(object sender, EventArgs e)
        {
            Random r = new Random();
            string str = null;
            for (int i = 0; i < 5; i++)
            {
                int rNumber = r.Next(0, 10); //产生5个验证码随机数
                str += rNumber.ToString();

            }

            Bitmap bmp = new Bitmap(150, 120);
           //创建一个GDI对象
            Graphics g = Graphics.FromImage(bmp); //可以理解为将位图作为画布

            //绘制验证码上面的数字
            for (int i = 0; i < 5; i++)
            {
                Point p=new Point(i*20,0); //此处的相对位置，不是相对窗体的，而是相对于pictureBox控件的 
                string[] font = {"微软雅黑","宋体","黑体","隶书","仿宋" };
                Color[] colors = { Color.Yellow, Color.Blue, Color.Black, Color.Red, Color.Green };
                
                g.DrawString(str[i].ToString(), new Font(font[r.Next(0,5)],20,FontStyle.Bold),new SolidBrush(colors[r.Next(0,5)]), p); //此处注意字体对象包括字体、像素、加粗与否等等

                
            }

            //绘制验证码上面的线
            for (int i = 0; i < 50; i++)
            {
                Point p1 = new Point(r.Next(0, bmp.Width), r.Next(0, bmp.Height));
                Point p2 = new Point(r.Next(0, bmp.Width), r.Next(0, bmp.Height));
                g.DrawLine(new Pen(Brushes.Green), p1, p2);
            }

            //将验证码上面加一些小点点
            for (int i = 0; i < 500; i++)
            {
                Point p3 = new Point(r.Next(0, bmp.Width), r.Next(0, bmp.Height));
                bmp.SetPixel(p3.X,p3.Y,Color.Yellow);
            }
            //将画好的位图赋值给Image属性,即将画好的图片镶嵌到pictureBox中
            pictureBox1.Image = bmp;
        }
    }
}

实现效果图：