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From: bernie@eric.ecr.mu.oz (Bernie Kirby)
Newsgroups: comp.windows.x
Subject: Re: 3d rotation in room coords?
Summary: Here is one alternative...
Message-ID: <6999@munnari.oz.au>
Date: 6 Mar 91 07:54:59 GMT
References: <9103050342.AA20065@maui.coral.com>
Sender: news@cs.mu.oz.au
Lines: 102

In article <9103050342.AA20065@maui.coral.com>, tomt@maui.coral.COM (Tom Tulinsky) writes:
> 
> I'd like to allow the user to do 3d rotations of an object in the
> 'room' coordinate system; i.e. y is toward the ceiling, x is to his
> right, and z is out of the screen (rt-handed).  I want this to be true
> even after he has done some rotations....  The naive way of
> implementing rotations accumulates them so that a 90 deg. y rotation,
> the x axis is now pointing out of the screen, where the room z axis
> is.  
> 
> I've tried everything I can think of, and can't get it to work.
> 
> My latest version, (using the Vogle package from uunet, somewhat like

	Here is a Vogle program that presents one alternative...
	When you press button 1 (on the mouse) it rotates about X,
	when you press button 2 (on the mouse) it rotates about Y,
	when you press button 3 (on the mouse) it rotates about Z.

	When you press all 3 buttons it exits.

	The rotations are proportional to the x position of the cursor
	and continue to accumulate as long as the button is pressed.

	Bernie.

----------
#include <vogle.h>
#define R2D	(1.0 / D2R)

main()
{
	int             but, i, j;
	float           x, y;
	float           x_rot, y_rot, zrot, xrot, yrot;

	prefsize(512, 512);
	vinit("");	/* Get device from envirionment */

	makeobj(1);
		color(1);
		move(0.0, 0.0, 0.0);
		draw(0.4, 0.0, 0.0);
		drawchar('x');
		color(2);
		move(0.0, 0.0, 0.0);
		draw(0.0, 0.4, 0.0);
		drawchar('y');
		color(3);
		move(0.0, 0.0, 0.0);
		draw(0.0, 0.0, 0.4);
		drawchar('z');
	closeobj();


	backbuffer();

	zrot = yrot = xrot = 0.0;

	while ((but = slocator(&x, &y)) <= 4) {	/* get mouse x,y */

		color(BLACK);
		clear();


		/*
		 * This one rotates about the normal orthogonal unrotated
		 * axes... but needs button 1 for about Y button 2 for
		 * about X, button 3 for Z.
		 */
		pushmatrix();	/* Save original... */
			translate(.4, 0.0, 0.0);
			rotate(yrot, 'y');
			rotate(xrot, 'x');
			rotate(zrot, 'z');
			if (but == 1) {
				xrot += 100.0 * -x;
			} else if (but == 2) {
				yrot += 100.0 * -x;
			} else if (but == 4) {
				zrot += 100.0 * -x;
			}

			callobj(1);
		popmatrix();
		/*
		 * This lot does it the normal way... ie if you rotate
		 * about the X-axis then rotate about Y the Y rotation
		 * is about the new X-rotated axis.
		 */
		pushmatrix();
			y_rot = 100.0 * -x;
			x_rot = 100.0 * -y;
			translate(-0.4, 0.0, 0.0);
			rotate(y_rot, 'y');	/* do y rot */
			rotate(x_rot, 'x');	/* do x rot */
			callobj(1);
		popmatrix();

		swapbuffers();
	}
}