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From: oster@dewey.soe.berkeley.edu (David Phillip Oster)
Newsgroups: comp.windows.x
Subject: Re: Widget tracking
Message-ID: <20907@ucbvax.BERKELEY.EDU>
Date: Tue, 22-Sep-87 17:45:48 EDT
Article-I.D.: ucbvax.20907
Posted: Tue Sep 22 17:45:48 1987
Date-Received: Thu, 24-Sep-87 07:12:37 EDT
References: <870922-063108-11818@Xerox>
Sender: usenet@ucbvax.BERKELEY.EDU
Reply-To: oster@dewey.soe.berkeley.edu.UUCP (David Phillip Oster)
Organization: School of Education, UC-Berkeley
Lines: 29

The way the problem of non-square buttons is solved on the Macintosh
is two-fold. 

First, there is a collection of subroutines for manipulating arbitrary
sets of polygons (drawing them, rescaling them, checking if a point is
inside, doing union, intersection, set difference.)  The internal
representation is a Ycoordinate sorted list of Xcoordinate sorted list
of pixels that are inside the set of polygons.

However, some shapes (like those of icons) are too jagged for this
representation to be efficient. In these cases, a bit map (called a
"mask") is used to give the shape of the object against the icon.

Now, suppose you want to see if a mouse coordinate point is inside one
of these little monsters.
1.) check to see if the point is inside the bounding rectangle.
2.) if it is, check to see if it is inside the actual object. In the
case of the set of polygons, the way you do this is obvious given the
internal representation.  In the case of a bitmap, you just translate
the point into the local coordiantes of the bitmap, and see if that
bit is on.

In either case, if the mouse point is in the widget, you consume the
mouse point. If it is not in this widget, you pass the point on to any
object that may be under you.

--- David Phillip Oster            --My Good News: "I'm a perfectionist."
Arpa: oster@dewey.soe.berkeley.edu --My Bad News: "I don't charge by the hour."
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