c++ - CreateCompatibleDC() 失败

Question

我正在使用 win32 制作 2D 动画。到目前为止，我的程序加载了一组从资源创建的 HBITMAP 对象。当在下面的代码中从“OnUpdate()”调用 CreateCompatibleDC() 时，动画期间会出现问题。在多次调用 OnUpdate 函数后，未创建 HDC 对象(可能未在内存中分配)。当调用 DeleteDC() 删除 HDC 对象时，这会导致意外结果。这是来自 main.cpp 的更新函数代码:

    void OnUpdate(
             HWND hwnd)
{
    PAINTSTRUCT ps;
    HDC hdc = BeginPaint(hwnd,&ps);
    if(!hdc)
    {
        MessageBox(NULL, L"Failed to Create Compatible DC - 'hdc' in OnUpdate()", L"ALERT", MB_OK);
        PostMessage(hwnd, WM_DESTROY, NULL, NULL);
    }
    HPALETTE hpalT = SelectPalette(hdc,hpal,FALSE);

    BITMAP bm;
    HDC hdcMem = CreateCompatibleDC(hdc);
    if(!hdcMem)
    {
        MessageBox(NULL, L"Failed to CreateCompatibleDC - 'hdcMem' in OnUpdate()", L"ALERT", MB_OK);
        PostMessage(hwnd, WM_DESTROY, NULL, NULL);
    }
    SelectBitmap(hdcMem, bkgMain);
    GetObject(bkgMain, sizeof(bm), &bm);
    BitBlt(backDC, 0, 0, bm.bmWidth, bm.bmHeight, hdcMem, 0, 0, SRCCOPY);

    // Clean up.
    if(!DeleteDC(hdcMem))
    {
        MessageBox(NULL, L"Failed to DeleteDC - 'hdcMem' in OnUpdate()", L"ALERT", MB_OK);
        PostMessage(hwnd, WM_DESTROY, NULL, NULL);
    }
    SelectPalette(hdc,hpalT,FALSE);
    EndPaint(hwnd,&ps);
}

Answer 1

什么是SelectBitmap()？如果它是 SelectObject() 的包装器/别名|那么你正在泄漏位图。

SelectBitmap(hdcMem, bkgMain); 

您应该在删除旧位图之前将其选回 DC:

This function returns the previously selected object of the specified type. An application should always replace a new object with the original, default object after it has finished drawing with the new object.