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Path: utzoo!watmath!watnot!watcgl!fdfishman
From: fdfishman@watcgl.UUCP (Flynn D. Fishman)
Newsgroups: net.micro.amiga
Subject: Screen(Page)Flipping (or how the west was won)
Message-ID: <913@watcgl.UUCP>
Date: Sun, 10-Aug-86 23:15:11 EDT
Article-I.D.: watcgl.913
Posted: Sun Aug 10 23:15:11 1986
Date-Received: Mon, 11-Aug-86 03:21:38 EDT
Distribution: net
Organization: U of Waterloo, Ontario
Lines: 72

Of some interest to
>From 3comvax!mykes Thu Aug  7 09:15:59 EDT 1986
>From sun!cmcmanis Sun Aug 10 12:15:48 EDT 1986

I recently (yesterday) implemented a method of page flipping for
the experiments here.

What I did was create two screens (I guess windows would work fine
also)  and then I drew one image on one screen and the other
image on the other screen.  It is then possible to use the
intuition command ScreenToFront(screen), to toggle between the two screens.
You can then remove the flicker using the graphics command
WaitBOVP(ViewPort), or WaitTOF(); before toggling the screen.

Questions:
1) Does this take longer than a millisecond?
2) Does this use the Blitter chip and therefore effect the
     8520A-b chip we use for the timer?
3) Is this a good way to do things, assuming that we do not care
     about the user getting access to intuition?

P.S. there is also a ScreenToBack(screen) command and
WindowToFront(Window), WindowToBack(Window) if you want to use
Windows.  Windows might also have another advantage in that you
do not have to define a window to be the entire screen but rather
only a small portion of the screen, therefore saving memory.

There is also another method that could be used, although is is
somewhat limited if you are using a lot of colours (or shapes),
but is faster, and less of a memory hog.
You could place a different image on a different bit plane, and then
change the colour map.
i.e. lets say you have to black and white images.
1) you would define a two bitplane window
2) Set Draw Mode to COMPLEMENT{XOR} (i.e. SetDrMd(RastPort, COMPLEMENT) )
3) Set the pen colour to 1 (i.e. SetAPen(RastPort, 1)
4) Draw the first image
5) Set the pen colour to 2 (i.e. SetAPen(RastPort, 2)
6) Draw the second image
7) then to flash the image one, you would set Colour 1 AND colour 3
     to white (i.e. SetRGB4(ViewPort, 1, 15, 15, 15);
                      SetRGB4(ViewPort, 3, 15, 15, 15);
     and colour 2 to Black (SetRGB4(ViewPort, 2, 0, 0, 0);
  The reason you also set colour 3 to white is since where ever
  both images intersect the colour will be 3
  i.e. colour 1 = %01, 2 = %10 so 1 XOR 2 = (%10 XOR %01 = %11) = 3
8) to show the second image you would turn colour 2 and colour 3 white
       and colour 1 black

This will work with up to 4 black and white (or red and green) images in 
Hi-res mode and 5 (b&w) images in low-res mode. And would also work for 
two 4 colour images in both modes, however the colour maps get
more complex.

Again I would ask that anybody, and everybody please comment on
these two methods, in any way they feel like.

-- 

      FDFISHMAN (Flynn D. Fishman) @ WATCGL

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