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Diffstat (limited to 'qb.c')
| -rw-r--r-- | qb.c | 86 |
1 files changed, 86 insertions, 0 deletions
@@ -0,0 +1,86 @@ +/* + * 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))); +} |