在電腦螢幕上畫圖

在Window上有一些軟體可以在電腦螢幕上畫圖,這是怎麼做的呢?我查了一些相關的資料,發現,實際上在Window系統上跟本就不可能直接向電腦的顯示器螢幕輸出自己所繪的圖,那些在DOS時代用系統中斷的做法在Window上不行了!!!那麼那些軟體是怎麼畫的呢,實際上有很多軟體採用了我在這裡的一個做法.如果有興趣可以試試喲:)

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

namespace BitBltScreen
{
 /// <summary>
 /// ShowScreen 的摘要說明。
 /// </summary>
 public class ShowScreen : System.Windows.Forms.Form
 {
  private const int SRCCOPY = 0xCC0020;

  [System.Runtime.InteropServices.DllImportAttribute("User32.dll")]
  private static extern IntPtr GetDesktopWindow();

  [System.Runtime.InteropServices.DllImport("gdi32.dll")]
  public static extern long BitBlt (IntPtr hdcDest, int nXDest, int nYDest, int nWidth, int nHeight, IntPtr hdcSrc, int nXSrc, int nYSrc, int dwRop);

  [System.Runtime.InteropServices.DllImportAttribute("User32.dll")]
  private static extern IntPtr GetDC(IntPtr hWnd);

  [System.Runtime.InteropServices.DllImportAttribute("User32.dll")]
  private static extern int ReleaseDC(IntPtr hWnd, IntPtr hDC);

  private Bitmap m_Image;//臨時用的位元影像
  private Point m_SPoint;//畫線的起始點
  private Point m_EPoint;//畫線的結束點
  private Graphics m_Graphics;//畫線用的繪圖物件
  private Color m_LineColor;
  private System.Windows.Forms.ContextMenu contextMenu1;
  private System.Windows.Forms.MenuItem menuItem1;
  private System.Windows.Forms.MenuItem menuItem2;

  /// <summary>
  /// 必需的設計器變數。
  /// </summary>
  private System.ComponentModel.Container components = null;

  public ShowScreen()
  {
   //
   // Windows 表單設計器支援所必需的
   //
   InitializeComponent();
   this.Location = new Point(0,0);
   this.Size = new Size(Screen.PrimaryScreen.Bounds.Width, Screen.PrimaryScreen.Bounds.Height);

   m_LineColor = Color.FromArgb(255,0,0);//初始化的紅色
  }

  #region Windows 表單設計器產生的程式碼
  /// <summary>
  /// 清理所有正在使用的資源。
  /// </summary>
  protected override void Dispose( bool disposing )
  {
   if( disposing )
   {
    if(components != null)
    {
     components.Dispose();
    }
   }
   base.Dispose( disposing );
  }

  /// <summary>
  /// 設計器支援所需的方法 - 不要使用代碼編輯器修改
  /// 此方法的內容。
  /// </summary>
  private void InitializeComponent()
  {
   this.contextMenu1 = new System.Windows.Forms.ContextMenu();
   this.menuItem1 = new System.Windows.Forms.MenuItem();
   this.menuItem2 = new System.Windows.Forms.MenuItem();
   //
   // contextMenu1
   //
   this.contextMenu1.MenuItems.AddRange(new System.Windows.Forms.MenuItem[] {
                       this.menuItem1,
                       this.menuItem2});
   //
   // menuItem1
   //
   this.menuItem1.Index = 0;
   this.menuItem1.Text = "CopyScreen(&C)";
   this.menuItem1.Click += new System.EventHandler(this.menuItem1_Click);
   //
   // menuItem2
   //
   this.menuItem2.Index = 1;
   this.menuItem2.Text = "Exit(&E)";
   this.menuItem2.Click += new System.EventHandler(this.menuItem2_Click);
   //
   // ShowScreen
   //
   this.AutoScaleBaseSize = new System.Drawing.Size(6, 14);
   this.ClientSize = new System.Drawing.Size(292, 270);
   this.ContextMenu = this.contextMenu1;
   this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.None;
   this.Name = "ShowScreen";

  }
  #endregion

  private void menuItem1_Click(object sender, System.EventArgs e)
  {
   LoadScreen();
  }

  private void menuItem2_Click(object sender, System.EventArgs e)
  {
   this.Close();
  }

  public void LoadScreen()
  {
   IntPtr desk = GetDesktopWindow();//得到電腦的最上層視窗
   IntPtr screenDC = GetDC(desk);//得到視窗的畫圖裝置控制代碼

   //產生一個和螢幕大小一樣的位元影像
   m_Image = new Bitmap(Screen.PrimaryScreen.Bounds.Width, Screen.PrimaryScreen.Bounds.Height);
   Graphics g = Graphics.FromImage(m_Image);//從這個位元影像建立一個畫圖對象
   IntPtr theDC = g.GetHdc();//得到這位元影像的畫圖對象裝置控制代碼
   
   //把最上層視窗的拷貝放到位元影像裡面,以備重畫時使用
   long tmpLong = BitBlt(theDC, 0, 0, Screen.PrimaryScreen.Bounds.Width, Screen.PrimaryScreen.Bounds.Height, screenDC, 0, 0, SRCCOPY);

   g.ReleaseHdc(theDC);//刪除位元圖畫圖裝置控制代碼
   ReleaseDC(this.Handle, screenDC);//刪除最上層視窗畫圖裝置控制代碼
  }

  protected override void OnPaint(PaintEventArgs e)
  {
   base.OnPaint (e);
   //視窗重畫時繪製位元影像
   if (m_Image != null)
   {
    e.Graphics.DrawImage(m_Image,0,0);
   }
  }

  protected override void OnMouseDown(MouseEventArgs e)
  {
   base.OnMouseDown (e);
   //滑鼠按下的時候記下畫線起點
   m_SPoint = new Point(e.X, e.Y);
   //建立畫圖用的對象
   if (m_Graphics == null)
   {
    m_Graphics = this.CreateGraphics();
   }
  }
  protected override void OnMouseMove(MouseEventArgs e)
  {
   base.OnMouseMove (e);
   if (e.Button == MouseButtons.Left)
   {
    //如果滑鼠左鍵按下就畫圖,這裡是一條紅色的直線
    m_Graphics.DrawImage(m_Image,0,0);//這裡這麼調用就是為了清除原來的線,我不知道怎麼做更好,所以...
    Point tmpPoint = new Point(e.X, e.Y);
    m_Graphics.DrawLine(new Pen(m_LineColor), m_SPoint, tmpPoint);//畫一條新的線.

    m_EPoint = tmpPoint;//記下新的點
   }
  }
  protected override void OnMouseUp(MouseEventArgs e)
  {
   base.OnMouseUp (e);
   //在滑鼠鍵抬起時到到位元影像上記下來
   Graphics tmpGraphics = Graphics.FromImage(m_Image);
   tmpGraphics.DrawLine(new Pen(m_LineColor), m_SPoint, m_EPoint);
  }
 }
}

這時就可以把代碼複製下來試試嘍,哈~哈~

不過在使用時,要先把螢幕取下來喲,要不就沒有效果了:)
  private void button1_Click(object sender, System.EventArgs e)
  {
   ShowScreen ss = new ShowScreen();
   ss.LoadScreen();
   ss.Show();
  }