Path: utzoo!yunexus!geac!syntron!jtsv16!uunet!seismo!sundc!pitstop!sun!amdcad!ames!sgi!msc@canth.SGI.COM
From: msc@canth.SGI.COM (Mark Callow)
Newsgroups: comp.windows.news
Subject: Re: Canvases in negative space
Summary: problem description
Keywords: Transformations
Message-ID: <21066@sgi.SGI.COM>
Date: 25 Oct 88 23:36:10 GMT
Article-I.D.: sgi.21066
References: <646@ecrcvax.UUCP>
Sender: daemon@sgi.SGI.COM
Organization: Silicon Graphics, Inc., Mountain View, CA
Lines: 25

There are two problems here:

1.	movecanvas moves the current canvas to x y relative to its parent.
	The problem is that x & y are in the coordinate system of the
	canvas being moved but are relative to the parents origin.  This
	is very tricky.
	
	This is fixed in xnews.  A new movecanvas operator takes an
	extra argument, the canvas, and moves it to an absolute x, y
	in the canvases own coordinate system.

2.	The second problem is that the underlying pixrect code does
	not understand how to make region pixrects that are to top
	or left of the primary pixrect.  The underlying code called
	by movecanvas as tests to prevent -ve x or y values.  It
	sets them to zero.

	I don't know if this is fixed in xnews.  We fixed it in our
	NeWS server.

--
From the TARDIS of Mark Callow
msc@sgi.sgi.com, ...{ames,decwrl,sun}!sgi!msc
"There is much virtue in a window.  It is to a human being as a frame is to
a painting, as a proscenium to a play.  It strongly defines its content."