c++ - Windows 7 和 ScreenShot.cpp GDI+ PNG 问题

Question

长时间使用 XP 没有问题。切换到 7 并尝试使用我以前运行的代码捕获屏幕截图不再有效。简单的概念和相对通用的代码...只需找到我调用的窗口并将其另存为 .png。有什么想法可以让这个坏男孩再次逃跑吗？无法使用我当前的设置进行调试，但它一直运行并在 bmp->save(...) 之后吐出错误消息...无法保存图像文件。编辑:也确实创建/保存了一个文件，但它是空白的并且没有写入。也许位图编码或 GDI 搞砸了？

bool CScreenShot::Snap(CString wintitle, CString file, CString& ermsg)
{
    ermsg = ""; // no error message

    // create screen shot bitmap
    EnumWinProcStruct prm = {0, (LPSTR)(LPCTSTR)wintitle, 0};

    // Find the descriptor of the window with the caption wintitle
    EnumDesktopWindows(0, EnumWindowsProc, (LPARAM)&prm);
    if(!prm.hwnd)
    {
        ermsg.Format("couldn't find window \"%s\"", wintitle);
        return false;
    }

    // Make the window the topmost window
    SetWindowPos(prm.hwnd, HWND_TOPMOST, 0, 0, 0, 0, SWP_NOSIZE | SWP_NOMOVE);
    Sleep(300);

    // Get device context for the top-level window and client rect
    HDC hDC = GetDC(prm.hwnd);
    RECT rc;
    GetClientRect(prm.hwnd, &rc);

    HDC memDC = CreateCompatibleDC(hDC);

    // Set the size and color depth for the screen shot image
    BITMAPINFO bmpInfo;
    memset(&bmpInfo, 0, sizeof(bmpInfo));
    bmpInfo.bmiHeader.biSize = sizeof(bmpInfo.bmiHeader);
    bmpInfo.bmiHeader.biWidth = rc.right - rc.left;
    bmpInfo.bmiHeader.biHeight = rc.bottom - rc.top;
    bmpInfo.bmiHeader.biPlanes = 1;
    bmpInfo.bmiHeader.biBitCount = 24;
    bmpInfo.bmiHeader.biCompression = BI_RGB;
    bmpInfo.bmiHeader.biSizeImage = bmpInfo.bmiHeader.biWidth * bmpInfo.bmiHeader.biHeight * 3;

    // Create memory buffer and perform a bit-block transfer of the color data from the window to the memory
    LPVOID  addr;
    HBITMAP memBM   = CreateDIBSection(memDC, &bmpInfo, DIB_RGB_COLORS, &addr, 0, 0);

    HGDIOBJ stdBM   = SelectObject(memDC, memBM);
    BOOL    OK      = BitBlt(memDC, 0, 0, bmpInfo.bmiHeader.biWidth, bmpInfo.bmiHeader.biHeight, hDC, 0, 0, SRCCOPY);
    ReleaseDC(prm.hwnd, hDC);

    SetWindowPos(prm.hwnd, HWND_NOTOPMOST, 0, 0, 0, 0, SWP_NOSIZE | SWP_NOMOVE);

    // Initialize GDI+.
    GdiplusStartupInput gdiplusStartupInput;
    ULONG_PTR           gdiplusToken;
    if(GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL) != Ok)
    {
        ermsg.Format("couldn't start GDI+");
        return false;
    }

    // Create a Bitmap object for work with images defined by pixel data from the GDI HBitmap and the GDI HPalette.
    Bitmap* bmp = ::new Bitmap(memBM, DIB_RGB_COLORS);
    SelectObject(memDC, stdBM);
    DeleteObject(memBM);
    DeleteDC(memDC);

    // Find the encoder for "image/png" mime type
    CLSID encoderClsid;
    EncoderParameters encoderParameters;

    GetEncoderClsid(L"image/png", &encoderClsid);

    encoderParameters.Count = 0;

    // Convert file name to Unicode (wide-char) string.
    WCHAR   fn[_MAX_PATH];
    MultiByteToWideChar(CP_THREAD_ACP, MB_PRECOMPOSED, file, file.GetLength() + 1, fn, _MAX_PATH);
    // Save the screen shot into the specified file using image encoder with the mime style "image/png"
    if(bmp->Save(fn, &encoderClsid, &encoderParameters) != Ok)
    {
        ermsg.Format("couldn't save image file \"%s\"", file);
        return false;
    }

    ::delete bmp;
    GdiplusShutdown(gdiplusToken);

    return true;
}

Answer 1

该错误消息表示您正在尝试将文件保存到您无权写入的文件夹中。 Program Files 等许多文件夹现在都受到保护。由于您没有在示例代码中包含路径，因此我无法确定这是否是实际问题。

编辑:另一种可能是位图构造不当，导致保存失败。构造函数的第二个参数应该是调色板的句柄，我认为 DIB_RGB_COLORS 在这里无效，您应该使用 NULL。 Microsoft documentation 中还有一些注意事项当您违反规则时，不同的操作系统版本可能会有不同的 react :

You are responsible for deleting the GDI bitmap and the GDI palette. However, you should not delete the GDI bitmap or the GDI palette until after the GDI+ Bitmap::Bitmap object is deleted or goes out of scope.

Do not pass to the GDI+ Bitmap::Bitmap constructor a GDI bitmap or a GDI palette that is currently (or was previously) selected into a device context.