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It's consecutive bug report of Bug 1526.

Platform: 32bit Ubuntu 12.04 under Vmware
SDL Version: SDL version 2.0.0 (stable)
Relevant files: SDL_x11window.c
Relevant functions: X11_ShowWindow, X11_HideWindow

Scenarios:

It's an QWidget window class and this->winId() will return the window handle of it. The program freezes after I called the following codes;

SDL_Window *window = SDL_CreateWindowFrom((void *)this->winId());   //OK
if(window == NULL)
{
    return;
}

SDL_Render *render = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED);  //WRONG, Freezing@!

When I followed in, I found that the program blocks at XIfEvent(display...

void
X11_HideWindow(_THIS, SDL_Window * window)
{
    SDL_WindowData *data = (SDL_WindowData *) window->driverdata;
    Display *display = data->videodata->display;
    XEvent event;

    if (X11_IsWindowMapped(_this, window)) {
        XUnmapWindow(display, data->xwindow);
        /* Blocking wait for "UnmapNotify" event */
        XIfEvent(display, &event, &isUnmapNotify, (XPointer)&data->xwindow);
        XFlush(display);
    }
}

then I applied the patch given by Bug 1526 patch, the code will look like:

void
X11_HideWindow(_THIS, SDL_Window * window)
{
    SDL_WindowData *data = (SDL_WindowData *) window->driverdata;
    Display *display = data->videodata->display;
    SDL_DisplayData *displaydata = 
	(SDL_DisplayData *) SDL_GetDisplayForWindow(window)->driverdata;
    XEvent event;

    if (X11_IsWindowMapped(_this, window)) {
        //XUnmapWindow(display, data->xwindow);
        XWithdrawWindow(display, data->xwindow, displaydata->screen);
        /* Blocking wait for "UnmapNotify" event */
        XIfEvent(display, &event, &isUnmapNotify, (XPointer)&data->xwindow);
        XFlush(display);
    }
}

So far, the X11_HideWindow doesn't block anymore, however, the XIfEvent got freezing at X11_ShowWindow, the code is as below:

void X11_ShowWindow(_THIS, SDL_Window * window)
{
    SDL_WindowData *data = (SDL_WindowData *) window->driverdata;
    Display *display = data->videodata->display;
    XEvent event;

    if (!X11_IsWindowMapped(_this, window)) {
        XMapRaised(display, data->xwindow);
        /* Blocking wait for "MapNotify" event.
         * We use XIfEvent because XWindowEvent takes a mask rather than a type,
         * and XCheckTypedWindowEvent doesn't block */
        XIfEvent(display, &event, &isMapNotify, (XPointer)&data->xwindow);
        XFlush(display);
    }
}

Expected behavior: SDL_CreateRenderer return successfully
Observed behavior: program freezes forever.