C# 製作螢幕截圖程式（三）：BitBlt API、裝置內容操作與系統匣常駐

核心步驟回顧

1. 建立顯示器裝置內容 (DC)：CreateDC("DISPLAY", ...)
2. 由 DC 建立 Graphics 物件
3. 依螢幕解析度建立同尺寸 Bitmap
4. 取得螢幕 DC 與 Bitmap DC
5. 呼叫 GDI BitBlt 將螢幕內容複製至 Bitmap
6. 釋放 DC、儲存 JPEG、顯示訊息

完整程式碼：Capture.cs

using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
using System.Drawing.Imaging;
using System.IO;
using System.Runtime.InteropServices;

public class Capture : Form
{
    private Container components = null;
    private Icon mNetTrayIcon = new Icon("Tray.ico");
    private Bitmap MyImage = null;
    private NotifyIcon TrayIcon;
    private ContextMenu notifyiconMnu;

    public Capture() { InitializeComponent(); }

    protected override void OnActivated(EventArgs e) { Hide(); }

    [DllImport("gdi32.dll")]
    private static extern bool BitBlt(IntPtr hdcDest, int nXDest, int nYDest, int nWidth, int nHeight,
        IntPtr hdcSrc, int nXSrc, int nYSrc, int dwRop);

    [DllImport("gdi32.dll")]
    private static extern IntPtr CreateDC(string lpszDriver, string lpszDevice, string lpszOutput, IntPtr lpInitData);

    public void capture(object sender, EventArgs e)
    {
        Visible = false;
        IntPtr dc1 = CreateDC("DISPLAY", null, null, IntPtr.Zero);
        Graphics g1 = Graphics.FromHdc(dc1);
        MyImage = new Bitmap(Screen.PrimaryScreen.Bounds.Width, Screen.PrimaryScreen.Bounds.Height, g1);
        Graphics g2 = Graphics.FromImage(MyImage);
        IntPtr dc3 = g1.GetHdc();
        IntPtr dc2 = g2.GetHdc();
        BitBlt(dc2, 0, 0, Screen.PrimaryScreen.Bounds.Width, Screen.PrimaryScreen.Bounds.Height, dc3, 0, 0, 13369376);
        g1.ReleaseHdc(dc3);
        g2.ReleaseHdc(dc2);
        MyImage.Save("c:\\MyJpeg.jpg", ImageFormat.Jpeg);
        MessageBox.Show("已將目前螢幕儲存至 C:\\MyJpeg.jpg！");
        Visible = true;
    }

    public void ExitSelect(object sender, EventArgs e)
    {
        TrayIcon.Visible = false;
        Close();
    }

    public override void Dispose()
    {
        base.Dispose();
        if (components != null) components.Dispose();
    }

    private void InitializeComponent()
    {
        TrayIcon = new NotifyIcon();
        TrayIcon.Icon = mNetTrayIcon;
        TrayIcon.Text = "C# 螢幕截圖程式";
        TrayIcon.Visible = true;

        MenuItem[] mnuItms = new MenuItem[3];
        mnuItms[0] = new MenuItem("擷取目前螢幕！");
        mnuItms[0].Click += new EventHandler(capture);
        mnuItms[1] = new MenuItem("-");
        mnuItms[2] = new MenuItem("結束系統");
        mnuItms[2].Click += new EventHandler(ExitSelect);
        mnuItms[2].DefaultItem = true;

        notifyiconMnu = new ContextMenu(mnuItms);
        TrayIcon.ContextMenu = notifyiconMnu;

        SuspendLayout();
        AutoScaleBaseSize = new Size(5, 13);
        ClientSize = new Size(320, 56);
        ControlBox = false; MaximizeBox = false; MinimizeBox = false;
        WindowState = FormWindowState.Minimized;
        ShowInTaskbar = false;
        Name = "capture";
        Text = "C# 螢幕截圖程式！";
        ResumeLayout(false);
    }

    static void Main() { Application.Run(new Capture()); }
}

執行畫面

圖01：C# 螢幕截圖程式執行介面（常駐系統匣）

總結

.NET Framework 功能豐富，但底層操作仍需呼叫 Win32 API。掌握 C# P/Invoke 呼叫 BitBlt、CreateDC 是關鍵。