Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!umich!samsung!cs.utexas.edu!sun-barr!newstop!sun!stpeter!cmcmanis
From: cmcmanis@stpeter.Sun.COM (Chuck McManis)
Newsgroups: comp.sys.amiga.tech
Subject: Re: How do you draw to the screen quickly?
Message-ID: <131690@sun.Eng.Sun.COM>
Date: 12 Feb 90 19:16:29 GMT
References: <1092@mindlink.UUCP>
Sender: news@sun.Eng.Sun.COM
Reply-To: cmcmanis@sun.UUCP (Chuck McManis)
Organization: Sun Microsystems, Mountain View
Lines: 25

In article <1092@mindlink.UUCP> a464@mindlink.UUCP (Bruce Dawson) writes:
>     [good comments about speeding up writing deleted]

> Warning:  When I last checked (several years ago I admit), DrawImage 
> didn't block menus (ie; didn't do a LockLayers()), meaning that menus
> could drop down and get drawn over by DrawImage(), thus munging the display.
> If this is still true, put your own LockLayers() calls around calls to
> DrawImage.

In fact what is going on here is that the Screen rastport doesn't have an
associated LayerInfo structure ('cuz it isn't layered) and this makes
it faster to write to because the software doesn't check for clipping or
"locked layers" but has the drawback that when Intuition thinks it has
the system "locked" (like when a menu is down) writing to the screen
will continue unconstrained. 

When righting to the Screen rastport you had better check your clipping
range and, if you use menus, do something like MENU_VERIFY to figure
out when menus are down.


--Chuck McManis
uucp: {anywhere}!sun!cmcmanis   BIX: cmcmanis  ARPAnet: cmcmanis@Eng.Sun.COM
These opinions are my own and no one elses, but you knew that didn't you.
"If it didn't have bones in it, it wouldn't be crunchy now would it?!"