Xlib Docs and/or How do I tell my WM to hide borders and title bar...

Carl Worth cworth at cworth.org
Wed Oct 20 06:23:08 PDT 2004

On Thu, 7 Oct 2004 17:38:20 -0400, Sergei Mutovkin wrote:
> I'm writing my first ever program with Xlib, either I look in the
> wrong places or there is no documentation with example available
> anywhere (except the most basic stuff)... I wonder about some very
> simple techniques...

First, it's worth pointing out that using raw Xlib is somewhat
incompatible with "simple techniques". It's generally much easier to use
a toolkit (such as GTK+ or QT) that sits on top of Xlib.

> 1. I want to create full screen window that will be on top of any
> other window...

That feature requires interaction with the window manager. The X
protocol doesn't mandate how this should occur, but external
conventions have grown up. First, there is the ICCCM (Inter-Client
Communication Conventions Manual):


And, more recently, the Extended Window Manager Hints (EWMH) which
extend the ICCCM:


I notice that EWMH supports _NET_WM_STATE property with a value of
_NET_WM_STATE_FULLSCREEN. So, if your window manager supports EWMH
(which any WM worth its salt should), then you should be just one
property away from getting this to work.

> 2.  How do I tell X to cache the graphics that I have drawn on the
> screen, so that if something gets on top of my window, I will not have
> re-draw everything after catching this event? (i.e. i don't want to
> sit in a loop listening and checking if event to redraw has arrived).

You can draw to a pixmap and set that pixmap to be the window background
with XSetWindowBackgroundPixmap. After that, the server will handle all
expose events so that you don't have to.

> 3. xClock application if loaded with Render enabled X has anti-aliased
> graphics... I wonder if anti-aliasing is achievable on simple graphics
> function of Xlib like XDrawLine, etc?

Not with these graphics calls. Xlib is intended to bind rather tightly
to the X protocol. And the protocol specifies precisely the pixelization
that must occur when drawing lines, etc.

The new approach, (and what xclock uses), is that the Render extension
provides a new protocol request for drawing antialiased, primitive
polygons (trapezoids). To make that easy to work with, you'll need code
to break up the shapes you want to draw into these trapezoids. That's
what the cairo library is intended to do:


With cairo, the analogue of XDrawLine would be:

	cairo_move_to (cr, x1, y1);
	cairo_line_to (cr, x2, y2);
	cairo_stroke (cr);

But with the advantage that you can specify the endpoints with sub-pixel
precision and that the coordinates can pass through an arbitrary affine
transformation (for scaling, rotating, etc.).

> 4. By default XDrawString doesn't use Anti-aliasing on the fonts, how
> would anyone go enabling it?

Again, XDrawString is a now old-fashioned way to draw text. It relies on
the text support inside the X server with server-side fonts. The new way
is to use client-side rendering of fonts with the glyph support in
XRender. Again, there are libraries to help with this such as Xft and

And, again, a modern toolkit will take care of most of these issues for
you automatically. The font work is there already, and we're working to
get the cairo graphics support into upcoming major releases of toolkits.

> I hope I didn't ask too many questions to annoy people here... I feel
> I'm ready to run and buy some book like "XLib In A Nutshell",

Something like that wouldn't be of much use for the modern approaches to
graphics in X. It's very likely that it's time for somebody to write a
new book.

I hope that helps,


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