为何代码没错却不显示Bmp图片？

switch(message)
{
case WM_CREATE:
    g_hbmBall = LoadBitmap(GetModuleHandle(NULL),MAKEINTRESOURCE(IDB_BALL));
    if(g_hbmBall == NULL)
        MessageBox(hwnd,TEXT("Couldn't load bitmap!"),TEXT("Error"),MB_OK | MB_ICONERROR);
    break;
case WM_COMMAND:
    wmId = LOWORD(wParm);
    switch (wmId)
    {
    case IDM_ABOUT:
        DialogBox(hInst,MAKEINTRESOURCE(IDD_ABOUTBOX),hwnd,AboutProc);
        break;
    case IDM_QUIT:
        DestroyWindow(hwnd);
        break;
    default:
        return DefWindowProc(hwnd, message, wParm, lParam);
    }
break;
case WM_PAINT:
    {
    PAINTSTRUCT ps;
    BITMAP bm;
    HDC hdc = BeginPaint(hwnd, &ps);
            HDC hdcMem = CreateCompatibleDC(hdc);
            SelectObject(hdcMem,g_hbmBall);

            GetObject(g_hbmBall, sizeof(bm), &bm);
            BitBlt(hdc, 0, 0, bm.bmWidth, bm.bmHeight, hdcMem,0, 0, SRCCOPY);
            DeleteDC(hdcMem);

            EndPaint(hwnd, &ps);

    break;
}
case WM_DESTROY:
    DeleteObject(g_hbmBall);
    PostQuitMessage(0);
    break;
default:
    return DefWindowProc(hwnd,message,wParm,lParam);