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From: guilford@sunbird.steinmetz (james d guilford)
Newsgroups: comp.sys.amiga
Subject: Double Buffering
Message-ID: <7768@steinmetz.steinmetz.UUCP>
Date: Thu, 5-Nov-87 07:23:13 EST
Article-I.D.: steinmet.7768
Posted: Thu Nov  5 07:23:13 1987
Date-Received: Sun, 8-Nov-87 03:45:10 EST
Sender: news@steinmetz.steinmetz.UUCP
Reply-To: guilford@csv.rpi.edu (james d guilford)
Organization: General Electric CRD, Schenectady, NY
Lines: 21
Keywords: double buffering, vertical retrace, screens
Summary: Do you have to sync with the vertical retrace


I am planning to write some animation-type software, and so  I looked
up double buffering in the RKM. It suggested that I create two screens
and two sets of copper lists, and then to flip screens, I just replace
the copper list pointers.

My question is whether I still have to sync with the vertical retrace.
It seems to me that even after updating the copper-list pointers, they
will not be used until the next scan begins. Thus it would not be safe
to start rendering into the other screen until after at least one
vertical blanking period. Is this right?

I am thinking of creating an interrupt handler on the vertical
blanking list which would have a private message port. When I change
the copper list points, I would send it a message. When the vertical
retrace occurs, it would reply to the message. When I see the reply, I
know it is safe to start rendering the next screen. Is this the best
way to go?


--JimG (guilford@csv.rpi.edu)