Path: chuka.playstation.co.uk!scea!greg_labrec@interactive.sony.com
From: Elliott Lee <tenchi@netmagic.net>
Newsgroups: scee.yaroze.programming.2d_graphics
Subject: Re: Rotation problems
Date: Fri, 06 Mar 1998 17:30:03 -0800
Organization: Cisco Systems
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Message-ID: <3500A31B.174703CD@netmagic.net>
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Yeah, I noticed the same weird behaviour too when rotating/sizing an
image of about 240x180 (or something like that).  This happened a lot
when the edges of the sprite were clipped by the viewing window as it
rotated around.  Maybe you can try breaking up your image into four
TIMs with their mx,my set to the inside corners and rotate about that?

	+--------------+--------------+
	|              |              |
	|              |              |
	|   Part 1     |   Part 2     |
	|              |              |
	|            mx|mx            |
	|            my|my            |
	+--------------+--------------+
	|            mx|mx            |
	|            my|my            |
	|   Part 3     |   Part 4     |
	|              |              |
	|              |              |
	|              |              |
	+--------------+--------------+

Yeah, you shouldn't have to do this, but maybe this might work.  One
problem I see with this already is that if the GPU is using fixed-
point vectors, you might end up seeing cracks where the four images
are joined together.

btw: what are you using 2+ 256x256x8 sprites for anyhoo?

Just a thought,
- e!
  tenchi@netmagic.net
  http://www.netmagic.net/~tenchi/


Robert Swan wrote:
> 
> I've been using rotation on sprites extensively in my game, but have
> come up with the following problems that REALLY annoy me. Is there
> something obvious I am doing wrong, or is it (as I assume) yet another
> bug in the psx (I was going to put 'another' in caps, but thought two
> capitalised words would merely annoy)
> 
> I have a sprite of size 256 by 256. (8 bit). It is perfectly within a
> texture page. I put it on screen, with about 5 others, and the
> computer slows right down; ridiculously so. Considering the processor
> can handle several hundred 32 by 32 sprites per frame, a couple of
> 256x256 should be no problem. But it gets worse. I really wanted to
> have these sprites zoomed by a factor of 2 and rotating. What happens
> is that the sprites flicker on and off at random, and slow down the
> game even further. I tried a workaround of using a 128x128 sprite and
> zooming it by four, but to no avail. here are some strange results
> I've found -
> 
> 256x256 sprite - very slow
> 256x256 sprite with rotation and/or scaling above x1 - not only very
> slow, but flickers on and off
> 128x128 sprite with scaling x2 works
> 128x128 sprite with scaling above x2 and/or rotation flickers and
> slows down
> smaller sprites than 128x128 when scaled above x3-4 with rotation it
> appears that certain angle values are ignored. Eg, when at angles
> 1024, 2048 etc it draws it as though at angle 0
> 
> These problems are wierd and annoying. It now means instead of having
> a lovely huge 256x256 sprite scaled to be over a screen in height I
> now have to settle for a measly 128x128 sprite that looks tiny
> (especially since I switched my game to hi res mode)
> 
> I've got enough packet workspace... any suggestions before I smash up
> my university's property?
> 
> Robert Swan
> rs108@mdx.ac.uk
> http://www.netyaroze-europe.com/~middex2