c++ - Win32 - 使用 GDI 对象的正确方法是什么？

Question

我正在 Win32 中制作一个简单的游戏。目前，我在主文件中全局声明了我的大部分绘图对象，这样我就不必删除它们或重新加载位图。所以基本上我所有的位图都加载到 WM_CREATE 中，然后不需要删除任何东西 - 有人告诉我，我可以只依靠系统在项目终止时清理我的资源。在 WM_PAINT(每秒调用 10 次左右)中，我有很多 BitBlt() 调用，以及相当多的 SelectObject() 调用。运行大约 10 - 15 分钟后，SelectObject()。什么会导致 SelectObject() 失败，我是否错误地使用了 GDI 对象？

示例:

// Top of the file
HDC hdc;
HDC hdcmem;
HDC hbcmem;
HBITMAP colorsprites, blackwhitesprites, nums;
HBITMAP hdcold, hdcbmold, hdcbm;

// Some functions to get the window ready

// More variables used for drawing:
HBITMAP bg, side, mainCont, tmpbm, tmpold, bm_left, bm_right, sidebg, win_bm;
PAINTSTRUCT ps;
RECT rc;
HDC tmphdc;
HDC tmp;
HFONT font;
HBRUSH hbr;
HPEN pen;
BITMAP structBitmapHeader;
HGDIOBJ hBitmap;
HCURSOR crosshairs = LoadCursorW(hInst, IDC_CROSS);
HCURSOR normal = LoadCursorW(hInst, IDC_ARROW);
POINT cursor;
bool addPass = false, ignorePass;

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message)
    {
        case WM_CREATE:
            hdc = GetDC(hWnd);
            hdcmem = CreateCompatibleDC(hdc);
            GetClientRect(hWnd, &rc);
            hdcbm = CreateCompatibleBitmap(hdc, rc.right, rc.bottom);
            hbcmem = CreateCompatibleDC(hdcmem);
            hdcbmold = (HBITMAP)SelectObject(hdcmem, hdcbm);

            // Load bitmaps
            bg                  = LoadBitmap(hInst, MAKEINTRESOURCE(IDB_BACKGROUND));
            mainCont            = LoadBitmap(hInst, MAKEINTRESOURCE(IDB_GAME_CONT));
            side                = LoadBitmap(hInst, MAKEINTRESOURCE(IDB_SIDEINFO));
            colorsprites        = LoadBitmap(hInst, MAKEINTRESOURCE(IDB_COLOR_SPRITES));
            blackwhitesprites   = LoadBitmap(hInst, MAKEINTRESOURCE(IDB_BLACKWHITE_SPRITES));
            sidebg              = LoadBitmap(hInst, MAKEINTRESOURCE(IDB_SIDEBG));
            nums                = LoadBitmap(hInst, MAKEINTRESOURCE(IDB_NUMBERS));
            bm_left             = LoadBitmap(hInst, MAKEINTRESOURCE(IDB_LEFT));
            bm_right            = LoadBitmap(hInst, MAKEINTRESOURCE(IDB_RIGHT));
            win_bm              = LoadBitmap(hInst, MAKEINTRESOURCE(IDB_VICTORY));
            if(bg == NULL || mainCont == NULL || side == NULL || colorsprites == NULL 
            || blackwhitesprites == NULL || sidebg == NULL || nums == NULL || bm_left == NULL 
            || bm_right == NULL)
                ThrowError("A bitmap failed to load.");

            break;

        case WM_PAINT:
            BeginPaint(hWnd, &ps);

            // SelectObject() and BitBlt() are called a lot in here

            EndPaint(hWnd, &ps);

            break;

        case WM_DESTROY:
            // System will clean up all GDI stuff - no need to delete anything
            PostQuitMessage(0);
            break;
    }
}

Answer 1

确保当您销毁 DC 时，您已将原始位图选回其中。当您的位图仍处于选中状态时，您永远不应销毁 DC。