From d1e9002f81f14fbfef1ebc4261edccd9eb97b72c Mon Sep 17 00:00:00 2001
From: rsc <devnull@localhost>
Date: Tue, 4 Jan 2005 21:23:01 +0000
Subject: 3D geometry

---
 src/libgeometry/qball.c | 66 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 66 insertions(+)
 create mode 100644 src/libgeometry/qball.c

(limited to 'src/libgeometry/qball.c')

diff --git a/src/libgeometry/qball.c b/src/libgeometry/qball.c
new file mode 100644
index 00000000..b73ecc51
--- /dev/null
+++ b/src/libgeometry/qball.c
@@ -0,0 +1,66 @@
+/*
+ * Ken Shoemake's Quaternion rotation controller
+ */
+#include <u.h>
+#include <libc.h>
+#include <draw.h>
+#include <stdio.h>
+#include <event.h>
+#include <geometry.h>
+#define	BORDER	4
+static Point ctlcen;		/* center of qball */
+static int ctlrad;		/* radius of qball */
+static Quaternion *axis;	/* constraint plane orientation, 0 if none */
+/*
+ * Convert a mouse point into a unit quaternion, flattening if
+ * constrained to a particular plane.
+ */
+static Quaternion mouseq(Point p){
+	double qx=(double)(p.x-ctlcen.x)/ctlrad;
+	double qy=(double)(p.y-ctlcen.y)/ctlrad;
+	double rsq=qx*qx+qy*qy;
+	double l;
+	Quaternion q;
+	if(rsq>1){
+		rsq=sqrt(rsq);
+		q.r=0.;
+		q.i=qx/rsq;
+		q.j=qy/rsq;
+		q.k=0.;
+	}
+	else{
+		q.r=0.;
+		q.i=qx;
+		q.j=qy;
+		q.k=sqrt(1.-rsq);
+	}
+	if(axis){
+		l=q.i*axis->i+q.j*axis->j+q.k*axis->k;
+		q.i-=l*axis->i;
+		q.j-=l*axis->j;
+		q.k-=l*axis->k;
+		l=sqrt(q.i*q.i+q.j*q.j+q.k*q.k);
+		if(l!=0.){
+			q.i/=l;
+			q.j/=l;
+			q.k/=l;
+		}
+	}
+	return q;
+}
+void qball(Rectangle r, Mouse *m, Quaternion *result, void (*redraw)(void), Quaternion *ap){
+	Quaternion q, down;
+	Point rad;
+	axis=ap;
+	ctlcen=divpt(addpt(r.min, r.max), 2);
+	rad=divpt(subpt(r.max, r.min), 2);
+	ctlrad=(rad.x<rad.y?rad.x:rad.y)-BORDER;
+	down=qinv(mouseq(m->xy));
+	q=*result;
+	for(;;){
+		*m=emouse();
+		if(!m->buttons) break;
+		*result=qmul(q, qmul(down, mouseq(m->xy)));
+		(*redraw)();
+	}
+}
-- 
cgit v1.2.3