winfrom-画图学习

namespace Painter
{
    partial class FormPainter
    {        
        private System.ComponentModel.IContainer components = null;

        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }
      
        private void InitializeComponent()
        {
            this.toolStrip1 = new System.Windows.Forms.ToolStrip();
            this.toolStripComboBoxMode = new System.Windows.Forms.ToolStripComboBox();
            this.pictureBox1 = new System.Windows.Forms.PictureBox();
            this.toolStrip1.SuspendLayout();
            ((System.ComponentModel.ISupportInitialize)(this.pictureBox1)).BeginInit();
            this.SuspendLayout();
            // 
            // toolStrip1
            // 
            this.toolStrip1.Items.AddRange(new System.Windows.Forms.ToolStripItem[] {
            this.toolStripComboBoxMode});
            this.toolStrip1.Location = new System.Drawing.Point(0, 0);
            this.toolStrip1.Name = "toolStrip1";
            this.toolStrip1.Size = new System.Drawing.Size(468, 25);
            this.toolStrip1.TabIndex = 0;
            this.toolStrip1.Text = "toolStrip1";
            // 
            // toolStripComboBoxMode
            // 
            this.toolStripComboBoxMode.Items.AddRange(new object[] {
            "画笔",
            "直线",
            "矩形",
            "圆形"});
            this.toolStripComboBoxMode.Name = "toolStripComboBoxMode";
            this.toolStripComboBoxMode.Size = new System.Drawing.Size(75, 25);
            this.toolStripComboBoxMode.Text = "画笔";
            // 
            // pictureBox1
            // 
            this.pictureBox1.Location = new System.Drawing.Point(0, 28);
            this.pictureBox1.Name = "pictureBox1";
            this.pictureBox1.Size = new System.Drawing.Size(456, 381);
            this.pictureBox1.TabIndex = 1;
            this.pictureBox1.TabStop = false;
            this.pictureBox1.MouseDown += new System.Windows.Forms.MouseEventHandler(this.FormPainter_MouseDown);
            this.pictureBox1.MouseMove += new System.Windows.Forms.MouseEventHandler(this.FormPainter_MouseMove);
            this.pictureBox1.MouseUp += new System.Windows.Forms.MouseEventHandler(this.FormPainter_MouseUp);
            // 
            // FormPainter
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 12F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(468, 421);
            this.Controls.Add(this.pictureBox1);
            this.Controls.Add(this.toolStrip1);
            this.Name = "FormPainter";
            this.Text = "Form1";
            this.toolStrip1.ResumeLayout(false);
            this.toolStrip1.PerformLayout();
            ((System.ComponentModel.ISupportInitialize)(this.pictureBox1)).EndInit();
            this.ResumeLayout(false);
            this.PerformLayout();

        }

        private System.Windows.Forms.ToolStrip toolStrip1;
        private System.Windows.Forms.ToolStripComboBox toolStripComboBoxMode;
        private System.Windows.Forms.PictureBox pictureBox1;
    }
}

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Windows.Forms;

namespace Painter
{
    public partial class FormPainter : Form
    {
        Graphics g;
        Bitmap img;
        Bitmap buf;
        Pen pen = new Pen(Color.Black, 3);

        public FormPainter()
        {
            InitializeComponent();

            img = new Bitmap(pictureBox1.Width, pictureBox1.Height);
            g = Graphics.FromImage(img);
        }

        bool isMouseDown = false;
        List points = new List();

        private void FormPainter_MouseDown(object sender, MouseEventArgs e)
        {
            Point p = new Point(e.X, e.Y);
            isMouseDown = true;
            points.Clear();
            points.Add(p);
            pictureBox1.Image = img;
        }

        private void FormPainter_MouseUp(object sender, MouseEventArgs e)
        {
            isMouseDown = false;
            img = buf; // 将上次 MouseMove 画的暂存结果取回
            pictureBox1.Image = img; // 然后显示出來
        }

        private void FormPainter_MouseMove(object sender, MouseEventArgs e)
        {
            Point p = new Point(e.X, e.Y);

            buf = new Bitmap(img); // 建立一个新的 buf 缓存区，画的时候
            Graphics g = Graphics.FromImage(buf);

            if (points.Count > 0 && isMouseDown)
            {
                Point pStart = points[0];
                Point pLast = points[points.Count - 1];
                if (toolStripComboBoxMode.Text.Equals("画笔"))
                {
                    Point p0 = pStart;
                    foreach (Point p1 in points)
                    {
                        g.DrawLine(pen, p0, p1);
                        p0 = p1;
                    }
                }
                else if (toolStripComboBoxMode.Text.Equals("直线"))
                {
                    g.DrawLine(pen, pStart, p);
                }
                else if (toolStripComboBoxMode.Text.Equals("矩形"))
                {
                    g.DrawRectangle(pen, pStart.X, pStart.Y, p.X - pStart.X, p.Y - pStart.Y);
                }
                else if (toolStripComboBoxMode.Text.Equals("圆形"))
                {
                    g.DrawEllipse(pen, pStart.X, pStart.Y, p.X - pStart.X, p.Y - pStart.Y);
                }
            }

            points.Add(p);
            pictureBox1.Image = buf;
        }

        //...

    }
}