Permanently changing the background

1. Not relevant to writing a screensaver module, only somewhat related.
2. create a pixmap as large as the screen;

     /* create a pixmap as large as the root window */
     pix = XCreatePixmap (dpy, root, wa.width, wa.height, wa.depth);
   

3. clear the pixmap

     /* clear the pixmap (not done by default) */
     XSetForeground(dpy, g, WhitePixelOfScreen(DefaultScreenOfDisplay(dpy)) );
     XFillRectangle (dpy, pix, g, 0, 0, wa.width, wa.height);
   

4. draw into it (use the same functions for drawing into a window but XClearArea and XClearWindow

     /* draw in the pixmap */
     for(i=0; i<500; i++) {
         /* set a random foreground color */
         XSetForeground(dpy, g, xcolors[random()%NCOLORS].pixel);
   
   
         /* draw a square */
         XFillRectangle (dpy, pix, g, random()%(wa.width-50),
                         random()%(wa.height-40), 50, 40);
     }
   

5. set it as the background of the root window

     /* set the pixmap as the background of the root window */
     XSetWindowBackgroundPixmap (dpy, root, pix);
   

6. clear the window (the background is not displayed unless some redrawing has to be made)

     /* clear the root window to make the pixmap visible */
     XClearWindow (dpy, root);