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