C#仿QQ实现简单的截图功能

//将上一篇的内容改成以下内容
// pictureBox1.Image = bmp;
FORM2 frm = new Form2();
frm.BaseImage = bmp;
frm.TopMost = true;
frm.Show();

#region Dll引用
[DllImport("User32.dll", EntryPoint = "GetDC")]
private extern static IntPtr GetDC(IntPtr hWnd);

[DllImport("User32.dll", EntryPoint = "ReleaseDC")]
private extern static int ReleaseDC(IntPtr hWnd, IntPtr hDC);

[DllImport("gdi32.dll")]
public static extern int GetDeviceCaps(IntPtr hdc, int nIndex);

[DllImport("User32.dll")]
public static extern int GetSystemMetrics(int hWnd);

const int DESKTOPVERTRES = 117;
const int DESKTOPHORZRES = 118;

const int SM_CXSCREEN = 0;
const int SM_CYSCREEN = 1;

#endregion

//<summary>
//获取DPI缩放比例
//</summary>
//<param name="dpiscalex"></param>
//<param name="dpiscaley"></param>
public static void GetDPIScale(ref float dpiscalex, ref float dpiscaley)
{
    int x = GetSystemMetrics(SM_CXSCREEN);
    int y = GetSystemMetrics(SM_CYSCREEN);
    IntPtr hdc = GetDC(IntPtr.Zero);
    int w = GetDeviceCaps(hdc, DESKTOPHORZRES);
    int h = GetDeviceCaps(hdc, DESKTOPVERTRES);
    ReleaseDC(IntPtr.Zero, hdc);
    dpiscalex = (float)w / x;
    dpiscaley = (float)h / y;
}


public Bitmap BaseImage { get; set; }

Graphics picGraphics;
//记录鼠标开始截图的位置
int startX = 0, startY = 0;
//记录鼠标结束截图的位置
int endX = 0, endY = 0;
//记录DPI缩放比例
float x = 0f, y = 0f;
public Form2()
{
    InitializeComponent();
}
private void Form2_Load(object sender, EventArgs e)
{
    

    GetDPIScale(ref x, ref y);
    picGraphics = pictureBox1.CreateGraphics();
}

private void pictureBox1_Paint(object sender, PaintEventArgs e)
{
    DrawRect(endX - startX, endY - startY,e.Graphics);
}

private void Form2_KeyPress(object sender, KeyPressEventArgs e)
{
    //按下esc退出
    if (e.KeyChar == 27)
    {
        this.Close();
    }
}

//完成截图
private void lbSucess_Click(object sender, EventArgs e)
{
    int clip_w = (int)((endX - startX) * x) - 4, clip_h = (int)((endY - startY) * y) - 4;
    if (clip_w < 1 || clip_h < 1)
    {
        return;
    }
    //获取截图
    Bitmap clipBmp = new Bitmap(clip_w, clip_h);
    Graphics g = Graphics.FromImage(clipBmp);
    g.CopyFromScreen((int)(startX * x) + 2, (int)(startY * y) + 2, 0, 0, new Size(clip_w, clip_h), CopyPixelOperation.SourceCopy);
    //将截图设置到剪切板
    Clipboard.SetImage(clipBmp);
    g.Dispose();
    this.Close();
}

private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
{
    //隐藏操作面板
    panel1.Visible = false;
    //记录鼠标开始截图的位置
    if (e.Button == MouseButtons.Left)
    {
        startX = e.X;
        startY = e.Y;
        endX = 0; endY = 0;
    }
}

private void pictureBox1_MouseMove(object sender, MouseEventArgs e)
{
    if (e.Button == MouseButtons.Left)
    {
        //绘制截图区域
        DrawRect(e.X - startX, e.Y - startY, picGraphics);
    }
}

private void pictureBox1_MouseUp(object sender, MouseEventArgs e)
{
    //截图完成
    if (e.Button == MouseButtons.Left)
    {
        endX = e.X;
        endY = e.Y;

        DrawRect(endX - startX, endY - startY, picGraphics);
        if (endX > startX && endY > startY)
        {
            //显示操作面板
            Thread.Sleep(100);
            panel1.Location = new Point(e.X - panel1.Width, e.Y + 5);
            panel1.Visible = true;
           
        }
    }
}

//绘制截图区域
private void DrawRect(int w, int h,Graphics g)
{
    Bitmap img = (Bitmap)BaseImage.Clone();

    //双缓冲技术画矩形,防止重影和抖动
    Graphics Painter = Graphics.FromImage(img);
    Painter.DrawRectangle(new Pen(Color.Red), startX * x, startY * y, w * x, h * y);
    g.DrawImage(img, 0, 0, img.Width / x, img.Height / y);

    Painter.Dispose();
    img.Dispose();
}