GLX and Removing Window Borders 
By Jaya Kanajan, SGI

H1. Introduction:

Sometimes having window borders is good, but when you're trying to go
full screen, havng a window border is a problem. So this ultra-short
article is simply to answer the question that we were asked at a
recent meeting: "I have my GL app ported and running with ProPack
1.3-VW on my 550 but I can't get rid of the window borders for some
reason.".

H1. Details

There are several ways to remove winodw borders, one is to instruct
the window manager manually by adding an entry to the applications
Xdefaults file like myapp*border: 0

This works, because the X server start scripts are setup to read the
Xdefaults and app-defaults files on startup in order to set properties
and preferences for various applications. However, that's not too
handy if you want to be able to go back and forth with having a border
versus not having a border easily. You can solve this problem using
(X11) XChangeProperty to tell the window manager (at least Motif
compliant window managers) to remove window border and other
decorations. 

H1. Conclusion
Use the Xdefaults/app-defaults mechanism if your application is always
full screen. If you want to do it within your own code, use the
XChangeProperty method to suggest removing window decorations. I
tested the follwing application on my Silicon Graphics 550 with
ProPack 1.3-VW on a VR7 graphics card and it works fine.

H1. Example Application

rmwmborder.c
===============================================================================
/* 
 *  jaya@sgi.com
 *  glx without window border example
 */

#include <X11/Xlibint.h>
#include <Xm/MwmUtil.h>
#include <GL/gl.h>
#include <GL/glx.h>
#include <stdio.h> 

static Atom wm_atom = 0;

Window makewindow(Display* dpy, int w, int h, int x, int y) {
    XSetWindowAttributes winattribs;
    Colormap cmap;
    XVisualInfo* vis;
    Window win;
    GLXContext ctxt;
    PropMwmHints hints;

    int attribs[] = { GLX_RGBA, GLX_DOUBLEBUFFER, None };

    vis = glXChooseVisual( dpy, DefaultScreen( dpy ), attribs );
 
    cmap = XCreateColormap( dpy, RootWindow(dpy, vis->screen), vis->visual,
                            AllocNone );

    winattribs.colormap = cmap;
    winattribs.border_pixel = 0;
    winattribs.background_pixel = 0;
    win = XCreateWindow( dpy, RootWindow(dpy, vis->screen),
                         x, y, w, h, 0, vis->depth, 
                         InputOutput, vis->visual, 
                         CWColormap|CWBorderPixel|CWBackPixel,
                         &winattribs );
    
   wm_atom = XInternAtom(dpy, "_MOTIF_WM_HINTS", False);
   hints.decorations = 0x0; 
   hints.flags |= MWM_HINTS_DECORATIONS; 
   XChangeProperty(dpy, win, wm_atom, wm_atom, 32,
                   PropModeReplace, (unsigned char *)&hints,
                   PROP_MOTIF_WM_HINTS_ELEMENTS);
    XStoreName(dpy, win, "drawpixels test");
    XSelectInput(dpy, win, ExposureMask | StructureNotifyMask |
                 KeyReleaseMask );
    XMapWindow( dpy, win );
    XFlush( dpy );
   
    ctxt = glXCreateContext( dpy, vis, 0, GL_TRUE );
    glXMakeCurrent(dpy, win, ctxt);

    glViewport(0, 0, (GLint)w, (GLint)h);
    glMatrixMode( GL_PROJECTION );
    glLoadIdentity();
    glOrtho(0, w, 0, h, -1, +1);
    glRasterPos2f(0.0, 0.0);
    
    return win;
}



int main(int argc, char **argv) {

    Display *dpy = XOpenDisplay(NULL);
    Window   win;
    GLenum gltype = GL_RGBA;
    GLenum glformat = GL_UNSIGNED_BYTE;
    int i,j;
    
    int w = 300;
    int h = 300;
    int x = 0;
    int y = 0;
    char *buf,*ptrbuf,*buf2,*ptrbuf2;
 
    win = makewindow(dpy,w,h,x,y);
    buf = (char*) malloc(w*h*4*sizeof(char));
    ptrbuf = buf;
    for (i=0;i<h;i++) {
      for(j=0;j<w;j++) {
        *buf++ = 255;
        *buf++ = 1;
        *buf++ = 255;
        buf++;
      }
    }

    buf2 = (char*) malloc(w*h*4*sizeof(char));
    ptrbuf2 = buf2;
    for (i=0;i<h;i++) {
      for(j=0;j<w;j++) {
        *buf2++ = 255 * ((double)(j+1) / (double)w);
        *buf2++ = 255 * ((double)(i+1) / (double)h);
        *buf2++ = 0;
        buf2++;
      }
    }
      
    for (i=0;i<h;i++) {
      if (i%2) {
        glDrawPixels(w,h,gltype,glformat,ptrbuf);
      } else {
        glDrawPixels(w,h,gltype,glformat,ptrbuf2);
      }
      glXSwapBuffers(dpy,win);
    }
    sleep(5);
    return 0;
}