打印不包括任何外部重叠窗口的面板内容的图像

Question

我有一些问题。
我在表单中有一个面板和一个图片框。
我想打开一个 Windows 应用程序（例如记事本）并将其作为面板的父级。
然后我想在 PictureBox 中显示面板内容的图像：

我的代码：

[DllImport("user32.dll", SetLastError = true)]
private static extern long SetParent(IntPtr hWndChild, IntPtr hWndNewParent);

[DllImport("user32.dll", SetLastError = true)]
private static extern long SetWindowPos(IntPtr hwnd, long hWndInsertAfter, long x, long y, long cx, long cy, long wFlags);

[DllImport("user32.dll", SetLastError = true)]
private static extern bool MoveWindow(IntPtr hwnd, int x, int y, int cx, int cy, bool repaint);

IntPtr appWin1;

private void Notepad_Button_Click(object sender, EventArgs e)
{
    ProcessStartInfo ps1 = new ProcessStartInfo(@"notepad.exe");
    ps1.WindowStyle = ProcessWindowStyle.Minimized;
    Process p1 = Process.Start(ps1);
    System.Threading.Thread.Sleep(5000); // Allow the process to open it's window
    appWin1 = p1.MainWindowHandle;
    // Put it into this form
    SetParent(appWin1, this.panel1.Handle);
}


private void timer1_Tick(object sender, EventArgs e)
{
    Bitmap bm = new Bitmap(panel1.Width, panel1.Height);
    Graphics g = Graphics.FromImage(bm);
    g.CopyFromScreen(0, 0, 0, 0, bm.Size);
    pictureBox1.Image = bm;
    
}

private void Form5_Load(object sender, EventArgs e)
{

}

private void panel1_Paint(object sender, PaintEventArgs e)
{

}

private void timer2_Tick(object sender, EventArgs e)
{
    MoveWindow(appWin1, 0, 0, this.panel1.Width, this.panel1.Height, true);
}

private void pictureBox1_Click(object sender, EventArgs e)
{

}

运行此代码：

问题是这样的：我只想获取面板内的内容，但在我的面板前面移动的任何其他窗口都包含在 PictureBox 中显示的位图中：

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如图所示，当外部页面放在panel1 上时，它也会出现在pictureBox1 中（图中的红框）。
我只希望记事本出现在pictureBox1 中，无论哪个窗口悬停在panel1 上。

Answer 1

由于您想将 Panel 的内容呈现到 Bitmap - 它托管外部应用程序 - 您不能使用 Control.DrawToBitmap()：托管应用程序的内容，父调用 SetParent()，将不会被打印。 由于您还想从渲染中排除可能悬停在面板上的任何其他窗口，您可以使用PrintWindow 函数，传递面板父窗体的句柄。
表单将收到WM_PRINT 或WM_PRINTCLIENT 消息，并将自己打印到指定的设备上下文：在这种情况下，从位图生成。

这不是屏幕截图：窗口将自身及其内容绘制到 DC，因此其他窗口是否悬停/部分或完全重叠都无关紧要，结果是相同的。

我正在使用DwmGetWindowAttribute，设置DWMWA_EXTENDED_FRAME_BOUNDS，来获取要打印的窗口的边界。它可能看起来冗余，但是，如果您的应用不是 DpiAware 并且您有一个高 Dpi 屏幕，那么在这种情况下它会显得较少冗余。最好有它，IMO。
此函数比GetWindowRect 或GetClientRect 更可靠，它将在可变 DPI 上下文中返回正确的度量。

你不能将子Window的句柄传递给这个函数，所以我使用父窗体的句柄来生成Bitmap，然后选择Panel所在的部分。这取决于：

[ParentForm].RectangleToClient([Child].RectangleToScreen([Child].ClientRectangle))

---

启动进程和父记事本的窗口到面板控件：

private void Notepad_Button_Click(object sender, EventArgs e)
{
    var psi = new ProcessStartInfo(@"notepad.exe") { WindowStyle = ProcessWindowStyle.Minimized };
    using (var p = Process.Start(psi)) {
        p.WaitForInputIdle();
        var handle = p.MainWindowHandle;
        if (handle != IntPtr.Zero) {
            SetParent(handle, panel1.Handle);
            MoveWindow(handle, 0, 0, panel1.Width, panel1.Height, true);
        }
    }
}

现在，当您想要将 Panel 所在的 Form 部分渲染到 Bitmap 时，调用 RenderWindow 并获取您感兴趣的部分：Panel 的 ClientRectangle。

using (var image = RenderWindow(this.Handle, true, false)) {
    if (image is null) return;
    if (WindowState == FormWindowState.Minimized) return;
    var panelRect = RectangleToClient(panel1.RectangleToScreen(panel1.ClientRectangle));
    pictureBox1.Image?.Dispose();
    pictureBox1.Image = image.Clone(panelRect, PixelFormat.Format32bppArgb);
}

// [...]

public static Bitmap RenderWindow(IntPtr hWnd, bool clientAreaOnly, bool tryGetFullContent = false)
{
    var printOption = clientAreaOnly ? PrintWindowOptions.PW_CLIENTONLY : PrintWindowOptions.PW_DEFAULT;
    printOption = tryGetFullContent ? PrintWindowOptions.PW_RENDERFULLCONTENT : printOption;
    var hResult = DwmGetWindowAttribute(hWnd, DWMWINDOWATTRIBUTE.DWMWA_EXTENDED_FRAME_BOUNDS, out Rectangle dwmRect, Marshal.SizeOf<Rectangle>());
    if (hResult < 0) {
        Marshal.ThrowExceptionForHR(hResult);
        return null;
    }

    if (dwmRect.Width <= 0 || dwmRect.Height <= 0) return null;

    var bmp = new Bitmap(dwmRect.Width, dwmRect.Height);
    using (var g = Graphics.FromImage(bmp)) {
        var hDC = g.GetHdc();
        try {
            var success = PrintWindow(hWnd, hDC, printOption);
            if (!success) {
                // Failed, see what happened
                var win32Error = Marshal.GetLastWin32Error();
                return null;
            }
            return bmp;
        }
        finally {
            g.ReleaseHdc(hDC);
        }
    }
}

Win32 声明：

[DllImport("user32.dll", SetLastError = true)]
static extern IntPtr SetParent(IntPtr hWndChild, IntPtr hWndNewParent);

[DllImport("user32.dll", SetLastError = true)]
static extern bool MoveWindow(IntPtr hWnd, int x, int y, int nWidth, int nHeight, bool bRepaint);

public enum PrintWindowOptions : uint
{
    PW_DEFAULT = 0,
    PW_CLIENTONLY = 1,
    PW_RENDERFULLCONTENT = 2  // Undocumented. Use, e.g., with a WebBrowser
}

[DllImport("user32.dll", SetLastError = true)]
static extern internal bool PrintWindow(IntPtr hwnd, IntPtr hDC, PrintWindowOptions nFlags);

public enum DWMWINDOWATTRIBUTE : uint
{
    DWMWA_NCRENDERING_ENABLED = 1,      // [get] Is non-client rendering enabled/disabled
    DWMWA_NCRENDERING_POLICY,           // [set] DWMNCRENDERINGPOLICY - Non-client rendering policy - Enable or disable non-client rendering
    DWMWA_TRANSITIONS_FORCEDISABLED,    // [set] Potentially enable/forcibly disable transitions
    DWMWA_ALLOW_NCPAINT,                // [set] Allow contents rendered In the non-client area To be visible On the DWM-drawn frame.
    DWMWA_CAPTION_BUTTON_BOUNDS,        // [get] Bounds Of the caption button area In window-relative space.
    DWMWA_NONCLIENT_RTL_LAYOUT,         // [set] Is non-client content RTL mirrored
    DWMWA_FORCE_ICONIC_REPRESENTATION,  // [set] Force this window To display iconic thumbnails.
    DWMWA_FLIP3D_POLICY,                // [set] Designates how Flip3D will treat the window.
    DWMWA_EXTENDED_FRAME_BOUNDS,        // [get] Gets the extended frame bounds rectangle In screen space
    DWMWA_HAS_ICONIC_BITMAP,            // [set] Indicates an available bitmap When there Is no better thumbnail representation.
    DWMWA_DISALLOW_PEEK,                // [set] Don't invoke Peek on the window.
    DWMWA_EXCLUDED_FROM_PEEK,           // [set] LivePreview exclusion information
    DWMWA_CLOAK,                        // [set] Cloak Or uncloak the window
    DWMWA_CLOAKED,                      // [get] Gets the cloaked state Of the window. Returns a DWMCLOACKEDREASON object
    DWMWA_FREEZE_REPRESENTATION,        // [set] BOOL, Force this window To freeze the thumbnail without live update
    PlaceHolder1,
    PlaceHolder2,
    PlaceHolder3,
    DWMWA_ACCENTPOLICY = 19
}

[DllImport("dwmapi.dll", SetLastError = true)]
static extern internal int DwmGetWindowAttribute(IntPtr hwnd, DWMWINDOWATTRIBUTE dwAttribute, out Rectangle pvAttribute, int cbAttribute);