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From: meekins@tortoise.cis.ohio-state.edu (timothy lee meekins)
Newsgroups: comp.sys.apple2
Subject: Re: Animation
Keywords: Animation
Message-ID: <108928@tut.cis.ohio-state.edu>
Date: 17 Apr 91 13:10:35 GMT
References: <1991Apr17.061057.22357@cs.uow.edu.au>
Sender: news@tut.cis.ohio-state.edu
Organization: The Ohio State University, Department of Computer and Information Science
Lines: 82

In article <1991Apr17.061057.22357@cs.uow.edu.au> u9050728@cs.uow.edu.au (Shane Kelvin Richards) writes:
>
>	Hello. I am hoping someone can help me. I am developing a set of
>animation routines for the //GS. So far its okay, BUT things are becoming
>a tad slow when many objects are on the screen. Heres how I am doing it..
>
>	If I want to put a shape on the screen, I go through a loop pulling
>off each background byte (that the shape will be using) anding it with the
>shapes mask (using a mask makes it really easy to have "see-through" holes
>in the shapes and so that the background moves around the shape if the 
>background and shape happen to fall in the same byte) then I ora the shape
>byte and place this calculated byte back on the screening (and yes I am
>using the shadow screen in bank $01 for faster reads). So this is the 
>basic process. It slows down quite considerably but I can't think of any
>other way of doing what  am trying to do. This is the place the shape
>down on top of the background nicely (so that it doesn't get jaggies if
>I had for instance just Stored the shape directly on the screen.
>
>       My question is, is my basic ideas/techniquie correct? Am I using
>the wrong method for fast shape manipulation. OR am I using the correct
>method and I should just try to improve upon my code and optimise where
>I can?
>
>      For simplicity I only let shapes move by 2 pixels so that they 
>always fall on a byte boundary. Also, I am usin the 320x200 resolution.
>
>	Any ideas, what other techniques are there?
>

If all your shapes are the same size, then try unrolling all your loops
in the shape drawing functions. Something like:

;
; On entry, X points to shape, Y points to screen
; Assume shape (for this example) is 8 bytes by 8 pixels.
;
DrawShape	phb		;Set to bank 1
		pea 	$0101
		plb
		plb

		lda	$2000+0*160+0,y
		and	>masktbl+0*8+0,x
		ora	>shapetbl+0*8+0,x
		sta	$2000+0*160+0,y

		lda	$2000+0*160+2,y
		and	>masktbl+0*8+2,x
		ora	>shapetbl+0*8+2,x
		sta	$2000+0*160+2,y

		...

		lda	$2000+6*160+6,y
		and	>masktbl+6*8+6,x
		ora	>shapetbl+6*8+6,x
		sta	$2000+6*160+6,y

		plb
		rts


It will take slightly more memory, but the speedup will be very noticable.


If you don't re-map the bank, and use long address for the screen instead,
you'll have to interchange the functions of the X & Y registers.

>

>-- 
>+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
>Shane Richards
>u9050728@cs.uow.edu.au
>+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-


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