tqball.c - plan9port - [fork] Plan 9 from user space
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       tqball.c (1374B)
       ---
            1 /*
            2  * Ken Shoemake's Quaternion rotation controller
            3  */
            4 #include <u.h>
            5 #include <libc.h>
            6 #include <draw.h>
            7 #include <stdio.h>
            8 #include <event.h>
            9 #include <geometry.h>
           10 #define        BORDER        4
           11 static Point ctlcen;                /* center of qball */
           12 static int ctlrad;                /* radius of qball */
           13 static Quaternion *axis;        /* constraint plane orientation, 0 if none */
           14 /*
           15  * Convert a mouse point into a unit quaternion, flattening if
           16  * constrained to a particular plane.
           17  */
           18 static Quaternion mouseq(Point p){
           19         double qx=(double)(p.x-ctlcen.x)/ctlrad;
           20         double qy=(double)(p.y-ctlcen.y)/ctlrad;
           21         double rsq=qx*qx+qy*qy;
           22         double l;
           23         Quaternion q;
           24         if(rsq>1){
           25                 rsq=sqrt(rsq);
           26                 q.r=0.;
           27                 q.i=qx/rsq;
           28                 q.j=qy/rsq;
           29                 q.k=0.;
           30         }
           31         else{
           32                 q.r=0.;
           33                 q.i=qx;
           34                 q.j=qy;
           35                 q.k=sqrt(1.-rsq);
           36         }
           37         if(axis){
           38                 l=q.i*axis->i+q.j*axis->j+q.k*axis->k;
           39                 q.i-=l*axis->i;
           40                 q.j-=l*axis->j;
           41                 q.k-=l*axis->k;
           42                 l=sqrt(q.i*q.i+q.j*q.j+q.k*q.k);
           43                 if(l!=0.){
           44                         q.i/=l;
           45                         q.j/=l;
           46                         q.k/=l;
           47                 }
           48         }
           49         return q;
           50 }
           51 void qball(Rectangle r, Mouse *m, Quaternion *result, void (*redraw)(void), Quaternion *ap){
           52         Quaternion q, down;
           53         Point rad;
           54         axis=ap;
           55         ctlcen=divpt(addpt(r.min, r.max), 2);
           56         rad=divpt(subpt(r.max, r.min), 2);
           57         ctlrad=(rad.x<rad.y?rad.x:rad.y)-BORDER;
           58         down=qinv(mouseq(m->xy));
           59         q=*result;
           60         for(;;){
           61                 *m=emouse();
           62                 if(!m->buttons) break;
           63                 *result=qmul(q, qmul(down, mouseq(m->xy)));
           64                 (*redraw)();
           65         }
           66 }