Question

我想截取没有焦点的窗口的截图。我的功能适用于某些窗口，但不适用于所有窗口，我不知道为什么。我试着抓住Bluestacks App Player的窗口，它运行得很好。但对于Nox App Player和其他一些游戏来说，它根本不起作用。我只得到一个窗口大小的黑色图像。

以下是目前的代码：

void screenshot_window(HWND handle) {
    RECT client_rect = { 0 };
    GetClientRect(handle, &client_rect);
    int width = client_rect.right - client_rect.left;
    int height = client_rect.bottom - client_rect.top;


    HDC hdcScreen = GetDC(handle);
    HDC hdc = CreateCompatibleDC(hdcScreen);
    HBITMAP hbmp = CreateCompatibleBitmap(hdcScreen, width, height);
    SelectObject(hdc, hbmp);

    BitBlt(hdc, 0, 0, width, height, hdcScreen, 0, 0, SRCCOPY);

    BITMAPINFO bmp_info = { 0 };
    bmp_info.bmiHeader.biSize = sizeof(bmp_info.bmiHeader);
    bmp_info.bmiHeader.biWidth = width;
    bmp_info.bmiHeader.biHeight = height;
    bmp_info.bmiHeader.biPlanes = 1;
    bmp_info.bmiHeader.biBitCount = 24;
    bmp_info.bmiHeader.biCompression = BI_RGB;

    int bmp_padding = (width * 3) % 4;
    if (bmp_padding != 0) bmp_padding = 4 - bmp_padding;

    BYTE *bmp_pixels = new BYTE[(width * 3 + bmp_padding) * height];;
    GetDIBits(hdc, hbmp, 0, height, bmp_pixels, &bmp_info, DIB_RGB_COLORS);

    BITMAPFILEHEADER bmfHeader;
    HANDLE bmp_file_handle = CreateFile("TestFile.bmp", GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);

    // Add the size of the headers to the size of the bitmap to get the total file size
    DWORD dwSizeofDIB = (width * 3 + bmp_padding) * height + sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);

    //Offset to where the actual bitmap bits start.
    bmfHeader.bfOffBits = (DWORD)sizeof(BITMAPFILEHEADER) + (DWORD)sizeof(BITMAPINFOHEADER);

    //Size of the file
    bmfHeader.bfSize = dwSizeofDIB;

    //bfType must always be BM for Bitmaps
    bmfHeader.bfType = 0x4D42; //BM

    DWORD dwBytesWritten = 0;
    WriteFile(bmp_file_handle, (LPSTR)&bmfHeader, sizeof(BITMAPFILEHEADER), &dwBytesWritten, NULL);
    WriteFile(bmp_file_handle, (LPSTR)&bmp_info.bmiHeader, sizeof(BITMAPINFOHEADER), &dwBytesWritten, NULL);
    WriteFile(bmp_file_handle, (LPSTR)bmp_pixels, (width * 3 + bmp_padding) * height, &dwBytesWritten, NULL);

    //Close the handle for the file that was created
    CloseHandle(bmp_file_handle);

    DeleteDC(hdc);
    DeleteObject(hbmp);
    ReleaseDC(NULL, hdcScreen);
    delete[] bmp_pixels;
}

Answer 1

许多应用程序可能会发生这种情况，目标窗口只是一个容器，并且不负责绘制消息。像记事本这样的标准win32应用程序不会这样。但是，您可能会遇到许多浏览器的问题。

您始终可以截取桌面窗口的屏幕截图。您可以获取目标窗口的屏幕坐标，然后bitblt目标窗口的那一部分。对您的代码进行以下更改：

//GetClientRect(handle, &client_rect);
GetWindowRect(handle, &client_rect);

//HDC hdcScreen = GetDC(handle);
HDC hdcScreen = GetDC(HWND_DESKTOP);

//BitBlt(hdc, 0, 0, width, height, hdcScreen, 0, 0, SRCCOPY);
BitBlt(hdc, 0, 0, width, height, hdcScreen, client_rect.left, client_rect.top, SRCCOPY);

//ReleaseDC(NULL, hdcScreen);
ReleaseDC(HWND_DESKTOP, hdcScreen);

在拍摄屏幕截图之前，目标窗口必须是屏幕上最顶部的可见窗口。例如，您可以按此顺序呼叫screenshot_window：

HWND hwnd = FindWindow(0, L"Calculator");
SetForegroundWindow(hwnd);
Sleep(1000);
screenshot_window(hwnd);

或者，您可以使用Dwm Thumbnail API在您自己的窗口中绘制目标窗口。但同样，您无法使用GetDC(my_hWnd)从窗口上的“Dwm Thumbnail”访问位图。同样，您必须使用GetDC(HWND_DESKTOP)拍摄桌面窗口的屏幕截图。这一次确保您自己的窗口是顶部窗口。

应用程序必须支持DPI，否则屏幕坐标将不匹配。

原始代码中也存在资源泄漏。 GetDC应使用相同的ReleaseDC而非handle

NULL清除

HDC hdcScreen = GetDC(handle);
...
//ReleaseDC(NULL, hdcScreen);
ReleaseDC(handle, hdcScreen);

Dim j As Double
For j = 1 To Worksheets.Count
        If Sheets(j).Range("E4").Value Like "Filters" Then
            ActiveSheet.Copy before:=Worksheets(1)
              ActiveSheet.Name = "data"
        End If
 Next j

C ++ WinAPI后台窗口的截图

1 个答案: