Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!rutgers!apple!lsr
From: lsr@Apple.COM (Larry Rosenstein)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Fast image changes
Message-ID: <524@internal.Apple.COM>
Date: 1 Feb 89 18:23:41 GMT
Sender: usenet@Apple.COM
Organization: Apple Computer, Inc.
Lines: 23
References:<243@usage.csd.unsw.oz> <10050074@accuvax.nwu.edu> <2661@munnari.oz>

In article <2661@munnari.oz> jkjl@munnari.oz (John Lim) writes:
> >You cannot use CopyBits from a VBL task. CopyBits is on the list of 
traps
> >which might move or purge memory.
> >
> David Dunham in MacTutor quoted Steve Brecher as saying that CopyBits
> only moves memory when you are saving a Picture. That was many months
> ago, so i dont know how valid this comment would be today.

Probably right, except that CopyBits (as do all Quickdraw drawing calls) 
use the current port's clipping and visible region.  At interrupt level, 
you can't be sure that the region handles will be consistent.  They could 
be in the process of being moved by the Memory Manager. 

I suppose one could lock down the clipRgn and visRgn, but under Color 
Quickdraw, there might be other handles that would need to be locked as 
well (eg, the pixmap handle).


Larry Rosenstein
lsr@Apple.COM or {sun, nsc}!apple!lsr

AppleLink: Rosenstein1