Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!bloom-beacon!apple!Apple.COM!lsr
From: lsr@Apple.COM (Larry Rosenstein)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Saving area under dialog boxes (Re: WingZ)
Message-ID: <1763@internal.Apple.COM>
Date: 10 May 89 17:32:36 GMT
References: <2993@tank.uchicago.edu>
Sender: usenet@Apple.COM
Distribution: na
Organization: Objects-R-Us,  Apple Computer, Inc.
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In article <2993@tank.uchicago.edu> ra_robert@gsbacd.uchicago.edu writes:

> "draws" on the screen I first draw it on the screen (e.g. on the 
simplest level
> with calls such as LineTo)  and then blit it to my offscreen buffer 
(from which
> I refresh my image) for permanent storage when the drawn object is done 
(i.e,
> on MouseUp).  Wouldn't there be times when you need to CopyBits from 
screen

You can't do the blit only on the mouse up and support automatic 
scrolling.  The user could draw a shape that is larger than the window, so 
part of the shape would be offscreen by the tim you did the blit.

I think most painting programs draw offscreen and do 1 blit to put the 
image on screen.  If you try MacPaint, you will see that it draws the 
object as it will appear (rather than drawing an XOR outline), and if you 
shrink the object the original image appears.  The only way you can do 
this properly is if you do a CopyBits each time the user moves the mouse.  

Each of these operatiosn will involve a small rectangle, and will be very 
fast.  I did this in my MacApp painting program, and it worked well in 
both B&W and color.

Larry Rosenstein, Apple Computer, Inc.
Object Specialist

Internet: lsr@Apple.com   UUCP: {nsc, sun}!apple!lsr
AppleLink: Rosenstein1