Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!mcvax!hp4nl!rivm!ccemdd
From: ccemdd@rivm.UUCP (Marco Dedecker)
Newsgroups: comp.sys.amiga
Subject: Re: how does one change the size of an iff picture
Message-ID: <1353@rivm05.UUCP>
Date: 1 Jun 89 07:28:40 GMT
References: <16520@louie.udel.EDU>
Organization: RIVM, Bilthoven, The Netherlands
Lines: 51

In article <16520@louie.udel.EDU>, MFM1%LEHIGH.BITNET@ibm1.cc.lehigh.edu (mark masters) writes:
> 
> 
> Okay, I've a question on how one could zoom in on a section of an IFF
> picture from within a program.  That is to say I've been working on an
> animation program, and I need to zoom in on a picture which has been
> loaded into memory and I have no Idea on how to change its size. Any
> help will be tremendously, incredibly, hugely appreciated.
> 
> mark
> <mfm1@lehigh>

Well actually, you can change the size of it, but by doing that you
won't zoom in.  If you want to zoom in you have to calculate a new
screen. In order to do this you have to know where you can find the
bitmaps of your IFF picture.

Suppose : 
- You have a picture 320*200, 5 bitplanes (32 colors).
- You wish to zoom in a screen of lets say 160*100  (1/4 of the screen).
- You wish to zoom in on the upper left corner (where X is).
	(0,0)		(160,0) 		(320,0)
		  X
	(0,100)		(160,100)		(320,100)

	(0,200)		(160,200)		(320,200)

What do you do :
- You define a second screen (320*200, 5 bitplanes). 
- You take the 1st bit from the first line of your original picture,
  and you display it twice on the first line of the new screen.
- After one line is done you duplicate the first line of the new picture
  to the second line of the new picture.

Example :

	The 1st byte of your picture : 10101100

	On the new picture it will become : 1100110011110000
	                                    1100110011110000

Keep in mind that if you are using this methode it will eat A LOT of
CPU time. You could try creating the new picture in fases (one
bitplane every vblank). You might also try using the blitter to
create the new picture.

I don't know if this is what you had in mind, but I hope it will be of
some help.


Marco Dedecker