ref: 63191949b911658c3774e727061fcf166ad9ace2
dir: /sys/src/libgeometry/qball.c/
/*
* Ken Shoemake's Quaternion rotation controller
*/
#include <u.h>
#include <libc.h>
#include <draw.h>
#include <stdio.h>
#include <event.h>
#include <geometry.h>
#define BORDER 4
static Point ctlcen; /* center of qball */
static int ctlrad; /* radius of qball */
static Quaternion *axis; /* constraint plane orientation, 0 if none */
/*
* Convert a mouse point into a unit quaternion, flattening if
* constrained to a particular plane.
*/
static Quaternion mouseq(Point p){
double qx=(double)(p.x-ctlcen.x)/ctlrad;
double qy=(double)(p.y-ctlcen.y)/ctlrad;
double rsq=qx*qx+qy*qy;
double l;
Quaternion q;
if(rsq>1){
rsq=sqrt(rsq);
q.r=0.;
q.i=qx/rsq;
q.j=qy/rsq;
q.k=0.;
}
else{
q.r=0.;
q.i=qx;
q.j=qy;
q.k=sqrt(1.-rsq);
}
if(axis){
l=q.i*axis->i+q.j*axis->j+q.k*axis->k;
q.i-=l*axis->i;
q.j-=l*axis->j;
q.k-=l*axis->k;
l=sqrt(q.i*q.i+q.j*q.j+q.k*q.k);
if(l!=0.){
q.i/=l;
q.j/=l;
q.k/=l;
}
}
return q;
}
void qball(Rectangle r, Mouse *m, Quaternion *result, void (*redraw)(void), Quaternion *ap){
Quaternion q, down;
Point rad;
axis=ap;
ctlcen=divpt(addpt(r.min, r.max), 2);
rad=divpt(subpt(r.max, r.min), 2);
ctlrad=(rad.x<rad.y?rad.x:rad.y)-BORDER;
down=qinv(mouseq(m->xy));
q=*result;
for(;;){
*m=emouse();
if(!m->buttons) break;
*result=qmul(q, qmul(down, mouseq(m->xy)));
(*redraw)();
}
}