A.D.A. Amiga Demoscene Archive

  Welcome guest! Please register a new account or log in

  

  

  

log in with SceneID

  

Demos Amiga Demoscene Archive Forum / Coding / Curious about an old school effect

 

Author Message
RetroCoder
Member
#1 - Posted: 27 Apr 2007 10:41
Reply Quote
Hi,
Now i've relieved my curiosity about shade bobs and roto zoomers I was wondering if anyone knew how this old school effect is done:

Screenshot 6 (vertical colour bars)
http://ada.untergrund.net/showdemo.php?demoid=558

Is it sprites or 1 pixel high bobs and some kind of modulo trick?

Thanks guys.
xeron
Member
#2 - Posted: 27 Apr 2007 11:08
Reply Quote
Oh. Seems someone did HAM-6 Kefratraz Bars before I did it in:
http://ada.untergrund.net/showdemo.php?demoid=518

Heres how I did it:

1) Set modulo to -40 so that the top line is stretched across the whole screen
2) Set up a copper list that starts the blitter to copy your 1-pixel high graphics into the bitplanes on every rasterline
3) Put the CPU into a loop that changes the blitter parameters so that the graphic is drawn in a sine-wave

On the screenshot you refer to, i'd imagine the text is sprites.
Toffeeman
Member
#3 - Posted: 27 Apr 2007 12:28
Reply Quote
Thank Xeron I always wonderd how this effect was done. So basically you redisplay the same line every time and just copy in your bob in the correct place each line. Very cool idea :0)
Toffeeman
Member
#4 - Posted: 27 Apr 2007 13:22
Reply Quote
RetroCoder check out these Copper lists ;0)

http://ada.untergrund.net/showdemo.php?demoid=524
RetroCoder
Member
#5 - Posted: 27 Apr 2007 15:00
Reply Quote
Xerox, that rocks - thanks for the explanation - very pretty intro you made there :)

So, I guess you only need a 1 pixel high bitplane and you don't clear the buffer each frame - is that correct?

Toffee, I vaguely remember seeing that Rebels demo for the first time - very cool :)

ps this site is awesome! :)
xeron
Member
#6 - Posted: 1 May 2007 11:43
Reply Quote
Thats right; the screen is basically 320x1, and you use the copper to trigger the drawing of a new bit in sync with the display.

At the beginning of each from you do have to clear the screen, but of course the screen is one 256th of the normal size so its very quick to do that :)

 

  Please register a new account or log in to comment

  

  

  

 

A.D.A. Amiga Demoscene Archive, Version 3.0