Path: utzoo!attcan!uunet!mcsun!ukc!tcdcs!bofin!cjmchale
From: cjmchale@cs.tcd.ie (Ciaran McHale)
Newsgroups: comp.windows.x
Subject: Re: porting unstructured graphics code to X
Message-ID: <1991Mar1.111215.11134@cs.tcd.ie>
Date: 1 Mar 91 11:12:15 GMT
References: <1991Feb25.212501.1776@yogi.fhhosp.ab.ca>
Organization: DSG, Dept. of Comp. Sci., Trinity College, Dublin.
Lines: 36

In <1991Feb25.212501.1776@yogi.fhhosp.ab.ca> henry@yogi.fhhosp.ab.ca writes:

>I have a pile of code that needs to run under X.  It all uses
>graphic primitive calls (lines, dots, crosses) that are PLOT-10 like.
>
>I'm unenthused about doing a lot of code rewrites to bundle graphics
>code into repaint procedures.
>
>Is there any easy way to port the code so that I can just draw into
>a window, and *not* have to worry about redrawing from Expose events?

There are advantages and disadvantages to the following
suggestion but here goes ...

X allows the programmer to create a pixmap, which can be
thought of as an off-screen window. The term "drawable"
refers to either a pixmap or a window. Most [%] of the Xlib
graphic routines to draw lines, circles etc work on
drawables, i.e., either pixmaps of windows. So you could
create a pixmap (using XCreatePixmap), and draw into that.
Then your expose handler simply uses XCopyArea to copy from
the pixmap to the exposed section of the window.

[%] You can clear a window (via XClearWindow or XClearArea)
but you can't clear a pixmap simply because a pixmap doesn't
have a background colour. Instead, if you want to clear a
pixmap then you should use XFillRectangle to fill it with a
suitable "background" colour.


Ciaran.
-- 
Ciaran McHale		"Verbosity says it all"			      ____
Department of Computer Science, Trinity College, Dublin 2, Ireland.   \  /
Telephone: +353-1-772941 ext 1538	FAX: +353-1-772204	       \/
Telex: 93782 TCD EI			email: cjmchale@cs.tcd.ie