Pete's QBASIC Site

If I'm crazy go ahead and tell me, but it seems that the following should be possible, if not actually rather simple:

I'm looking for an algorithm to simplify 3D (it doesn't have to be EXTREME '28th Century' 3D) graphics rotation, specifically regarding image rotation along the Z-axis.

Think of the old Atari coin-op game, "Battlezone". The enemy tanks (which were vector "draws") could rotate 180 degrees, by increments of around 10. They could face the player, face perpendicularly to the player in either direction, or be aligned along any of several angles in between. I would like to be able to make images do essentially the same thing, without having to compose (and code) every image. Here's what I'm thinking:

There ought to be a way to write a program to plot an image at any angle between 0 and 90. One should be able to provide this program with two images, a "front" (0 degree), and a "side" (90 degree) image. The program would, having read both images, utilize the algorithm to provide a corresponding (by most measures it would actually be a "conglomerate") image for the given angle (between 1 and 89).

Of course, one might well write a program to calculate said algorithm, but such would be way beyond my means.

I searched the web for hours for an answer before coming here to clutter up this forum. Any help would be greatly appreciated.

I would especially appreciate any help before carrying a digital camera out to my workshop, cutting a length of 2x4, painting to outline its edges, decorating two of its sides, photographing it at 0, 10, 20, 30, 40, 50, 60, 70, 80, and 90 degrees relative the camera, uploading the images, and working for hours to approximate the algorithm in question!!!

Heh.

Ehm, you mean 2d rotation I believe? Like a rotozoomer? The formula for that is:
RotatedX = ScreenX * COS(angle) - ScreenY * SIN(angle)
RotatedY = ScreenX * SIN(angle) + ScreenY * COS(angle)

For more info, check:
The first two are about rotation only. The thirs is about rotozoomers (so also zooming and optimization, this may be good if you want to use it in a game. Check the example code too)
http://www.petesqbsite.com/sections/tut ... ation.html
http://www.petesqbsite.com/sections/tut ... tation.txt
http://www.petesqbsite.com/sections/tut ... otate.html

Nothing is SIMPLE when you don't know! Especially if it involves a 2 by 4!

How many sites are you gonna post this on?

Ted

Hey! 2x4's, second only to Petroleum, make all you know of The World go 'round!

Heh!

I only posted on the 2 websites of which you are (apparently) aware. I have a bad habit of drinking and driving (gin and surfing), I must admit, and I wanted an answer to this question!

I think that I made my tragic mistake by misnaming the axis in question. fork the Z-axis, boys. I want to rotate an image about the Y axis.

Y.

As in WHY?

We're talking Y.

ahum.

ehm.

Anyway~

Oh dear. Not these conventions again. Do you know how to multiply matrices? Not code them in, but matrices do clarify it up quite a bit.

On a 2d coordinate system:
let R be the roational matrix
let P be the set of 2d points
let Q be the point you want
In your case, just switch the 'y's with the 'z's . This is the same thing as Codemss' presented equations, though in a shorter notation. DirectX and OpenGL use rotational matrices. If you can create a matrice class, and some functions for them (methods possibly), the work thereafter is very simple. Then a matrice can take care of 3d rotation, scaling, reflection, and other little manipulations. All you have to so is to know what numbers go where.

My rant probably seems hard to understand. I didn't understand it at first, and it took me some time to figure it out. But if you're going into 3d graphics and design, matrices are a very important tool.

I've got some programs that can do 3d graphics and rotation (with a movable camera!).

You also might want to use a depth array (is it a buffer?) so that things in the back can't be drawn above things in the front. But it'll take some work.