Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!sun-barr!newstop!sun!pepper!cmcmanis
From: cmcmanis%pepper@Sun.COM (Chuck McManis)
Newsgroups: comp.sys.amiga
Subject: Re: Denise/Paula/Agnus/Gary/Portia
Message-ID: <122977@sun.Eng.Sun.COM>
Date: 22 Aug 89 19:54:23 GMT
References: <1388@bnr-fos.UUCP> <713@neptune.UUCP> <522@tardis.Tymnet.COM> <4705@tekig5.PEN.TEK.COM>
Sender: news@sun.Eng.Sun.COM
Reply-To: cmcmanis@sun.UUCP (Chuck McManis)
Distribution: comp.sys.amiga
Organization: Sun Microsystems, Mountain View
Lines: 55


			NEW LAYOUT OF BITPLANES
              Addr   <---------- layout in memory --------->
             0x0000  +---------+---------+---------+---------+
             0x0140  |         |         |         |         |
              ...    |         |         |         |         |
             0xF9FF  +---------+---------+---------+---------+
                      <--bp0--> <--bp1--> <--bp2--> <--bp3-->

	Figure 1. Deven's drawing. (Addresses Assume 640 X 200 X 4 screen)

			TRADITIONAL LAYOUT OF BITPLANES
			Addr	<- layout ->
			0x0000  +----------+
			0x0050  |          |
			 ...    |          |<--bp0--> 
			0x3E80  +----------+
			0x3F00  |          |
			 ...    |          |<--bp1--> 
			0x7D00  +----------+
			0x7D80  |          |
			 ...    |          |<--bp2--> 
			0xBB80  +----------+
			0xBC00  |          |
			 ...    |          |<--bp3--> 
			0xF9FF  +----------+
         
	Figure 2. My Drawing (Addresses still assume a 640 X 200 screen)

In article <4705@tekig5.PEN.TEK.COM> (Wayne Knapp) writes:
> Except that that blitter is just way too slow to do smooth scrolling,
> except for maybe low-res 4 bitplane stuff.  High-res 4 bitplane, 
> requires over 100ms even just to clear the memory, a simple one
> source blit. 
>                                    Wayne Knapp

Wayne you overlooked what was being said. Would someone with a 1M Agnus
*please* code this up. I'd do it, but I don't have such a beast yet. 

The key is that the "new" way of laying out the bitmaps can scroll the
entire screen with all four bitplanes with a *single* blit. And while 
the blit will not complete in a single frame time, the absolute worst
side effect you would see would be *one line* of pixels that were the
wrong color. Contrast that to the current situation where *every* pixel
on the screen can be the wrong color because of one blit is finished 
and the next is setting up. 

As Deven mentioned the only problem is that Amiga's with the old Agnus
can't take advantage of this technique because their blitters can't do
the big blit necessary.

--Chuck McManis
uucp: {anywhere}!sun!cmcmanis   BIX: cmcmanis  ARPAnet: cmcmanis@sun.com
These opinions are my own and no one elses, but you knew that didn't you.
"A most excellent barbarian ... Genghis Kahn!"