Can't get Xlib window to display

tron_thomas · 03-12-2009, 11:34 PM

I am having trouble writing an Xlib application that displays a window. The most frustrating thing is that I've written applications like this before, and never had any problems. For some reason I cannot get this program to work properly. I'm running KDE and when I launch the program, a "button" for the application will appear on the application panel, however, no window will display. It is possible to right click on the panel button and select the Close item which will successfully close the window.

The following is source code that when built will exhibit the behaviour described above:

Code:

#include <cstring>
#include <X11/Xlib.h>
#include <GL/glx.h>

int main()
{
    Display* display = ::XOpenDisplay(NULL);

    int glXAttributes[] = 
    {
        GLX_RGBA,
        GLX_RED_SIZE, 1,
        GLX_GREEN_SIZE, 1,
        GLX_BLUE_SIZE, 1,
        GLX_DEPTH_SIZE, 1,
        GLX_DOUBLEBUFFER,
        None
    };

    XVisualInfo* visualInfo = ::glXChooseVisual(display, 0, glXAttributes);
    
    Window rootWindow = DefaultRootWindow(display);
    
    XSetWindowAttributes attributes;
    ::memset(&attributes, 0, sizeof(attributes));
    attributes.colormap = ::XCreateColormap(display, rootWindow,
        visualInfo->visual, AllocNone);

    int x = 0;
    int y = 0;
    
    unsigned int width = 640;
    unsigned int height = 480;

    Window window = ::XCreateWindow(display, rootWindow, x, y, width, height,
        0, visualInfo->depth, InputOutput, visualInfo->visual,
        CWBorderPixel | CWColormap, &attributes);
        
    ::XFree(visualInfo);
    
    Atom atom = ::XInternAtom(display, "WM_DELETE_WINDOW", False);
    ::XSetWMProtocols(display, window, &atom, 1);
    
    ::XSelectInput(display, window, ExposureMask | KeyPressMask |
        ButtonPressMask | ButtonReleaseMask | StructureNotifyMask);
    
    ::XMapWindow(display, window);
    
    bool loop = true;
    XEvent event;
    do{
        ::XNextEvent(display, &event);
        if(ClientMessage == event.type){
            if(event.xclient.data.l[0] == static_cast<long>(atom)){
                loop = false;
            }
        }
    }while(loop);
    
    ::XDeleteProperty(display, window, atom);
    ::XDestroyWindow(display, window);
    ::XFlush(display);
    ::XCloseDisplay(display);

    return 0;
}

What is needed so this program will successfully display a window?

fantas · 03-13-2009, 08:24 AM

Does it give you any error messages (i.e. when running your application from a terminal) ?
First thing I'd check in an OpenGL app is if OpenGL is generally supported (glXQueryExtension) and then deciding what to do next.

tron_thomas · 03-13-2009, 09:53 AM

I have always been launching the program from GDB, and I have never noticed the program emitting any error information. This is just another aspect that adds to the frustration of the problem.

OpenGL is definitely supported. Other application I've written like this use OpenGL and they work fine. I cannot determine what the difference is between this more recent application which doesn't work and the former applications what work just fine.

fantas · 03-13-2009, 10:25 AM

Could it be because of you specifying the bordersize as null but adding the CWBorderPixel mask ? Weird, but stranger things do happen sometimes.
Otherwise, did you try yet to replace the gl-specific arguments to XCreateWindow with "CopyFromParent" to rule out that it's something gl-specific ?

Well, that's at least the two next thoughts I had about your code. If they don't give any more hints I guess it's time to check all return values etc., and see where it all goes wrong.

paulsm4 · 03-13-2009, 12:09 PM

Hi -

It builds and runs fine for me:

SuSE Linux 9.3, X11 R6.8.2

Are you sure $DISPLAY is set correctly? Are you able to run your program directly from the command prompt? Do standard X clients (e.g. "xclock") run OK from the same command prompt?

Sorry I can't be of more help :-(

Your .. PSM

SciYro · 03-13-2009, 12:12 PM

Could it be your window manager? Your program works on my computer, showing a window with screen garabage inside it. (fvwm on gentoo)

Maybe try adding a flush after mapping the window?

tron_thomas · 03-13-2009, 11:40 PM

I changed:

Code:

Window window = ::XCreateWindow(display, rootWindow, x, y, width, height,
    0, visualInfo->depth, InputOutput, visualInfo->visual,
    CWBorderPixel | CWColormap, &attributes);

to

Code:

Window window = ::XCreateWindow(display, rootWindow, x, y, width, height,
    1, visualInfo->depth, InputOutput, visualInfo->visual,
    CWBorderPixel | CWColormap, &attributes);

and now the window is displaying. Thanks everyone for you help

fantas · 03-14-2009, 01:41 PM

So my first guess was right. Glad that it works now.

paulsm4 · 03-14-2009, 01:43 PM

Wow - that's odd!

I know that border_width must be 0 for an InputOnly window, but I wasn't aware of any restriction where it *couldn't* be zero...

SUGGESTION:
I think maybe fantas hit it on the head:

Quote:

Could it be because of you specifying the bordersize as null but adding the CWBorderPixel mask?

Try *removing* CWBorderPixel, change border_width back from 1 to 0, and see if it works now.

QUESTION:
I'm also curious about your version info:
a) platform (e.g. Ubuntu 8.04),
b) X Windows version,
... and ...
c) desktop Window Manager (e.g. KDE xy.z)

Thanx in advance .. PSM

tron_thomas · 03-14-2009, 02:14 PM

I removed the CWBorderPixel flag from the XCreateWindow and changed the border_width back to zero. The window failed to display.

I'm running Fedora 9 on an Intel Core2 Duo system.
X-Server version 11
KDE 4.2.0
NVIDIA GeForce 7600 GT/PCI/SSE2
Compiz Window Manager with Slate Horn Emerald theme.

fantas · 03-14-2009, 02:24 PM

Less weird now (at least to me as I would have been surprised that X11 could choke on such a situation), but still enough weird that a zero-size border should give such a result.
I have no ideas about KDE or Compiz though, but in this light it sounds like that's where the bug (if we can call it like that) originates from.