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From: lsr@apple.UUCP (Larry Rosenstein)
Newsgroups: comp.sys.mac
Subject: Re: Drawpicture from C - HELP!!
Message-ID: <6455@apple.UUCP>
Date: Mon, 12-Oct-87 13:09:57 EDT
Article-I.D.: apple.6455
Posted: Mon Oct 12 13:09:57 1987
Date-Received: Wed, 14-Oct-87 00:46:31 EDT
References: <773@sdcc18.ucsd.EDU>
Reply-To: lsr@apple.UUCP (Larry Rosenstein)
Organization: Advanced Technology Group, Apple Computer
Lines: 33
Keywords: Am I doing it wrong?!?

In article <773@sdcc18.ucsd.EDU> cs161aey@sdcc18.ucsd.EDU (Joe Gervais) writes:
>
>	I'm programing in Megmax C (v. 2.0 (?)) and after defining a picture
>and closing it, I can draw it in the original srcrect but if I try to move
>it I don't get anything.  I "believe" I'm doing it correctly, but I just
>don't get anything.  Even just offsetting the srcrect (so as not to change
>size and need scaling) it doesn't work.

This is a common problem with using pictures.  

When you open a picture, Quickdraw records the current state ofthe clipping
region in the picture.  When you draw a picture in a rectangle that is
offset from its creation rectangle, Quickdraw offsets the region as well.

The problem occurs because the default clipping in a new grafPort is the
largest possible rectangle.  Offsetting this rectangle by any amount causes
the coordinates to overflow, thus creating an empty region.  The empty
clipping region prevents anything from being drawn.

The solution is to always set the clipping before or right after calling
OpenPicture.  The general rule of thumb is to call ClipRect with the same
rectangle passed to OpenPicture.


-- 
Larry Rosenstein

Object Specialist
Apple Computer

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