C# 實現類 QQ 屏幕截圖（二）：鼠標交互邏輯

核心鼠標事件處理

雙擊確認截圖

private void ScreenBody_DoubleClick(object sender, EventArgs e)
{
    var me = (MouseEventArgs)e;
    if (me.Button == MouseButtons.Left && Rect.Contains(me.X, me.Y))
    {
        // 複製選區到剪貼板
        using (Bitmap bmp = new Bitmap(Rect.Width, Rect.Height))
        using (Graphics g = Graphics.FromImage(bmp))
        {
            g.CopyFromScreen(Rect.X + 1, Rect.Y + 1, 0, 0, Rect.Size);
            Clipboard.SetImage(bmp);
        }
        this.Close();
    }
}

鼠標按下：開始選區 / 移動選區 / 右鍵取消

private void ScreenBody_MouseDown(object sender, MouseEventArgs e)
{
    if (e.Button == MouseButtons.Left)
    {
        isDowned = true;
        if (!RectReady) // 首次按下：記錄起點
        {
            Rect.X = e.X; Rect.Y = e.Y;
            downPoint = new Point(e.X, e.Y);
        }
        else // 已有選區：記錄移動起點
        {
            tmpx = e.X; tmpy = e.Y;
        }
    }
    else if (e.Button == MouseButtons.Right)
    {
        if (!RectReady) { this.Close(); return; } // 無選區直接退出
        // 有選區：右鍵重置
        MainPainter.DrawImage(baseImage, 0, 0);
        RectReady = false;
    }
}

鼠標抬起：確認選區完成

private void ScreenBody_MouseUp(object sender, MouseEventArgs e)
{
    if (e.Button == MouseButtons.Left)
    {
        isDowned = false;
        RectReady = true; // 選區確定
    }
}

鼠標移動：拖動選區 / 調整大小 / 移動整個選區

private void ScreenBody_MouseMove(object sender, MouseEventArgs e)
{
    if (!RectReady) // 選區未確定：調整大小
    {
        if (isDowned)
        {
            using (Image img = DrawScreen((Image)baseImage.Clone(), e.X, e.Y))
                MainPainter.DrawImage(img, 0, 0);
        }
    }
    else // 選區已確定：判斷是否在選區內移動
    {
        if (Rect.Contains(e.X, e.Y) && isDowned)
        {
            // 計算偏移量
            Rect.X += e.X - tmpx;
            Rect.Y += e.Y - tmpy;
            tmpx = e.X; tmpy = e.Y;
            MoveRect((Image)baseImage.Clone(), Rect);
        }
    }
}

窗體加載初始化

private void ScreenBody_Load(object sender, EventArgs e)
{
    this.WindowState = FormWindowState.Maximized;
    MainPainter = this.CreateGraphics();
    pen = new Pen(Brushes.Blue);
    isDowned = false;
    baseImage = this.BackgroundImage;
    Rect = new Rectangle();
    RectReady = false;
}

狀態機總結

資源釋放提醒

• MainPainter = this.CreateGraphics() 獲取的 Graphics 需在 FormClosed 中 Dispose()。
• pen、baseImage 同理。
• 頻繁 Clone() 圖像可能導致內存壓力，建議改用 BufferedGraphics 或僅重繪髒矩形區域。