ref: eddb2d366ba452ff2993aa4c827150767a1fcc59
dir: /qball.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" #define MIN(a, b) ((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 */ q.r = 0; if(rsq > 1){ /* outside the sphere */ rsq = 1/sqrt(rsq); q.i = p.x*rsq; q.j = p.y*rsq; q.k = 0; }else{ 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 qball(Rectangle r, Point p0, Point p1, Quaternion *orient, Quaternion *axis) { Quaternion qdown, qdrag; Point2 rmin, rmax; Point2 v0, v1; /* unit sphere coords */ Point2 ctlcen; /* controller center */ double ctlrad; /* controller radius */ if(orient == nil) return; rmin = Vec2(r.min.x, r.min.y); rmax = Vec2(r.max.x, r.max.y); ctlcen = divpt2(addpt2(rmin, rmax), 2); ctlrad = MIN(Dx(r)/2, Dy(r)/2); v0 = divpt2(Vec2(p0.x-ctlcen.x, ctlcen.y-p0.y), ctlrad); v1 = divpt2(Vec2(p1.x-ctlcen.x, ctlcen.y-p1.y), ctlrad); qdown = mouseq(v0, axis); qdrag = mulq(mouseq(v1, axis), qdown); *orient = mulq(qdrag, *orient); }