1 /*
2  * Ken Shoemake's Quaternion rotation controller
3  */
4 #include <u.h>
5 #include <libc.h>
6 #include <draw.h>
7 #include <stdio.h>
8 #include <event.h>
9 #include <geometry.h>
10 #define	BORDER	4
11 static Point ctlcen;		/* center of qball */
12 static int ctlrad;		/* radius of qball */
13 static Quaternion *axis;	/* constraint plane orientation, 0 if none */
14 /*
15  * Convert a mouse point into a unit quaternion, flattening if
16  * constrained to a particular plane.
17  */
18 static Quaternion mouseq(Point p){
19 	double qx=(double)(p.x-ctlcen.x)/ctlrad;
20 	double qy=(double)(p.y-ctlcen.y)/ctlrad;
21 	double rsq=qx*qx+qy*qy;
22 	double l;
23 	Quaternion q;
24 	if(rsq>1){
25 		rsq=sqrt(rsq);
26 		q.r=0.;
27 		q.i=qx/rsq;
28 		q.j=qy/rsq;
29 		q.k=0.;
30 	}
31 	else{
32 		q.r=0.;
33 		q.i=qx;
34 		q.j=qy;
35 		q.k=sqrt(1.-rsq);
36 	}
37 	if(axis){
38 		l=q.i*axis->i+q.j*axis->j+q.k*axis->k;
39 		q.i-=l*axis->i;
40 		q.j-=l*axis->j;
41 		q.k-=l*axis->k;
42 		l=sqrt(q.i*q.i+q.j*q.j+q.k*q.k);
43 		if(l!=0.){
44 			q.i/=l;
45 			q.j/=l;
46 			q.k/=l;
47 		}
48 	}
49 	return q;
50 }
51 void qball(Rectangle r, Mouse *m, Quaternion *result, void (*redraw)(void), Quaternion *ap){
52 	Quaternion q, down;
53 	Point rad;
54 	axis=ap;
55 	ctlcen=divpt(addpt(r.min, r.max), 2);
56 	rad=divpt(subpt(r.max, r.min), 2);
57 	ctlrad=(rad.x<rad.y?rad.x:rad.y)-BORDER;
58 	down=qinv(mouseq(m->xy));
59 	q=*result;
60 	for(;;){
61 		*m=emouse();
62 		if(!m->buttons) break;
63 		*result=qmul(q, qmul(down, mouseq(m->xy)));
64 		(*redraw)();
65 	}
66 }