ref: 702e1d92ff4e270f5be88d1b5b190c4de758a101
dir: /qb.c/
/*
* Ken Shoemake's Quaternion rotation controller
* “Arcball Rotation Control”, Graphics Gems IV § III.1, pp. 175-192, August 1994.
*/
#include <u.h>
#include <libc.h>
#include <bio.h>
#include <thread.h>
#include <draw.h>
#include <memdraw.h>
#include <mouse.h>
#include <keyboard.h>
#include <geometry.h>
#include "libobj/obj.h"
#include "libgraphics/graphics.h"
#include "fns.h"
static int
min(int a, int b)
{
return a < b? a: b;
}
/*
* Convert a mouse point into a unit quaternion, flattening if
* constrained to a particular plane.
*/
static Quaternion
mouseq(Point2 p, Quaternion *axis)
{
double l;
Quaternion q;
double rsq = p.x*p.x + p.y*p.y; /* quadrance */
if(rsq > 1){ /* outside the sphere */
rsq = sqrt(rsq);
q.r = 0;
q.i = p.x/rsq;
q.j = p.y/rsq;
q.k = 0;
}else{ /* within the sphere */
q.r = 0;
q.i = p.x;
q.j = p.y;
q.k = sqrt(1 - rsq);
}
if(axis != nil){
l = dotq(q, *axis);
q.i -= l*axis->i;
q.j -= l*axis->j;
q.k -= l*axis->k;
l = qlen(q);
if(l != 0){
q.i /= l;
q.j /= l;
q.k /= l;
}
}
return q;
}
void
qb(Rectangle r, Point p0, Point p1, Quaternion *orient, Quaternion *axis)
{
Quaternion q, down;
Point2 rmin, rmax;
Point2 s0, s1; /* screen coords */
Point2 v0, v1; /* unit sphere coords */
Point2 ctlcen; /* controller center */
double ctlrad; /* controller radius */
rmin = Vec2(r.min.x, r.min.y);
rmax = Vec2(r.max.x, r.max.y);
s0 = Vec2(p0.x, p0.y);
s1 = Vec2(p1.x, p1.y);
ctlcen = divpt2(addpt2(rmin, rmax), 2);
ctlrad = min(Dx(r), Dy(r));
v0 = divpt2(subpt2(s0, ctlcen), ctlrad);
down = invq(mouseq(v0, axis));
q = *orient;
v1 = divpt2(subpt2(s1, ctlcen), ctlrad);
*orient = mulq(q, mulq(down, mouseq(v1, axis)));
}