From 702e1d92ff4e270f5be88d1b5b190c4de758a101 Mon Sep 17 00:00:00 2001
From: rodri <rgl@antares-labs.eu>
Date: Tue, 14 May 2024 16:40:49 +0000
Subject: use real lengths in solar. bring a qball for vis.

---
 qb.c | 86 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 86 insertions(+)
 create mode 100644 qb.c

(limited to 'qb.c')

diff --git a/qb.c b/qb.c
new file mode 100644
index 0000000..1485b9a
--- /dev/null
+++ b/qb.c
@@ -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)));
+}
-- 
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