Date: Sat, 09 Jul 2005 06:58:09 +0900 (JST)
Message-Id: <20050709.065809.78734215.garrigue at math.nagoya-u.ac.jp>
To: matthieu.dubuget at laposte.net
Cc: lablgtk at math.nagoya-u.ac.jp
Subject: Re: Double buffering ?
From: Jacques Garrigue <garrigue at math.nagoya-u.ac.jp>
In-Reply-To: <42CE8604.4080508 at laposte.net>
References: <42CE8604.4080508 at laposte.net>
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From: Matthieu Dubuget <matthieu.dubuget at laposte.net>

> I'm playing with lissajous.ml ($Id: lissajous.ml,v 1.9 2000/06/06 
> 03:51:04 garrigue Exp $), extracted from the example directory of lablgtk2.
> 
> I modified it to test drawing area as a tool to display living curves.
> 
> With my current implementation, the display is "fickering". This is 
> especially visible if the image displayed is not modified between two 
> exposures.
> 
>  I thought double buffering would allow to avoid this effect? And that 
> it was enabled by default with version 2 of gtk?

Double-buffering is enabled when drawing all widgets.
But lissajous.ml works at a lower level, by calling Gdk directly on an
on-screen window. This clearly bypasses double-buffering.
You can easily recover it by using a pixmap.
examples/timer.ml does this for instance: it first creates a pixmap,
draws on it, and then copies it to the screen. To avoid using too many
resources, it caches the pixmap and only creates a new one when the
size changes.

Jacques