A89: Re: Rotating Sprites

To: <assembly-89@lists.ticalc.org>
Subject: A89: Re: Rotating Sprites
From: "Sebastian Reichelt" <SebastianR@gmx.de>
Date: Wed, 7 Feb 2001 22:35:50 +0100
Organization: SeReSoft
References: <000701c0914b$bed86000$93504f40@ees.eesc.com>
Reply-To: assembly-89@lists.ticalc.org


Hi!

|     I have several ideas for some games, which require displaying a sprite
| at various angles. I remember something about using matrices to do this,
but
| I don't know how to implement this.  I'm looking for a C function which
can
| quickly rotate a sprite at various angles. Any ideas?

Depending on what you want, yes.  If the angles are just 90°, 180°, and
270°, this is rather easy to do.  180° just involves switching rows in the
sprite from the outside to the inside or verse vica.  90° and 270° are more
complicated:  You'll have to test each bit and put it in its new location.
I don't want to think about any details right now, but the fact is that it's
doable.

All other angles involve a lot of math, especially trigonometry.  For small
sprites, this also reduces quality a lot.  Calculating new positions for all
pixels is really slow as well.  I would recommend vectorizing your sprites
into polygons and calculating the new points for all corners of the
polygons.  Again, this involves trig; remember that floating point functions
are slow.  I don't want to go into any detail here; I assume you can do the
math.

Sorry if I wasn't able to help a lot.

Bye,
Sebastian

Follow-Ups:

A89: Re: Re: Rotating Sprites

From: "B Clark" <nix249@mich.com>

References:

A89: Rotating Sprites

From: "B Clark" <nix249@mich.com>