Path: utzoo!mnetor!uunet!lll-winken!lll-tis!ames!pasteur!ucbvax!UCONNVM.BITNET!STEIN
From: STEIN@UCONNVM.BITNET
Newsgroups: comp.sys.apple
Subject: Quickdraw
Message-ID: <8804122040.aa11841@SMOKE.BRL.ARPA>
Date: 13 Apr 88 01:42:00 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 55


I've started playing around with assembly language using the
GS Toolbox and am having some difficulty deciphering some
facts about Quickdraw's coordinate system from the
documentation I am using -- Michael Fischer's Apple IIGS
Technical Reference and Gary Little's Exploring the Apple
IIGS.  I think I have the concepts down, but the definitions
of various rectangles in those books seem to me to be
ambiguous and perhaps even contradictory.

The following is the state of my understanding.  I would
appreciate corrections and enlightenment.

There is a global coordinate system and a local coordinate
system.  Both are calibrated in pixels.  The global
coordinate system (I think) is tied to the hardware, with
the origin [0,0] representing the upper left hand corner of
the screen.  The lower right hand corner would usually be
[200,640] (with the vertical coord first, horizontal
second).

The local coordinate system seems to be an imaginary
coordinate system based on a theoretical underlying document
size supplied by the user.  The underlying document is
conceptualized as a rectangle.

When a window is defined, it is placed at a given location
on the screen (based on the upper left hand corner) at a
given size.  It can be placed there, and sized, via the
global coordinate system.

The content in the window shown on the screen is corresponds
to a rectangular portion of the underlying document.  The
size and placement of that portion, relative to the
underlying document, is indicated by the scroll bars.

I am virtually certain that the above description is
correct.  My major uncertainty deals with the terminology
used in the references I have, particularly BoundsRect and
PortRect.

PortRect seems to refer to the local coordinates of the
vertices of the window.  But I'm uncertain what BoundsRect
refers to.  Also, clearly there must be terminology
referring to the size of the display screen (or desktop?)
and the placement, in global coordinates, of the window on
the desktop.  These initial coordinates are passed to the
window manager when a window is defined, but the coordinates
(global) change when the window is resized or moved, and I
haven't recognized a reference to them.


ARPA:   stein%uconnvm.bitnet@mitvma.mit.edu        Alan H. Stein
BITNET: STEIN@UCONNVM                          University of Connecticut
UUCP:   ...ihnp4!psuvax1!UCONNVM.BITNET!STEIN        at Waterbury
CompuServe: 71545,1500  Genie:  ah.stein       Department of Mathematics