X-Git-Url: http://shamusworld.gotdns.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=src%2Fgeometry.cpp;h=82d24e84c492ca81e2f116b23b1d84d14fc53d1a;hb=dacd9dc2c1ac093e4945f7befaeb5ff1801a0f52;hp=f4918560990d8ddcd61709daf54aae49c6b4fadc;hpb=10cf4c797bed05831e976068b7504908279dc997;p=architektonas

diff --git a/src/geometry.cpp b/src/geometry.cpp
index f491856..82d24e8 100644
--- a/src/geometry.cpp
+++ b/src/geometry.cpp
@@ -525,6 +525,21 @@ Vector Geometry::GetNormalOfPointAndLine(Point p, Line * l)
 	return normal;
 }
 
+//
+// Returns the orientation of the points when traversed in order (from p1 to
+// p2 to p3).  +1 = CCW, -1 = CW, 0 = colinear
+//
+int Geometry::Orientation(Point p1, Point p2, Point p3)
+{
+	double xx = p2.x - p1.x, yy = p2.y - p1.y;
+	double aa = p3.x - p1.x, bb = p3.y - p1.y;
+
+	// Mult by -1 if screen coords already transformed
+	double zz = (xx * bb) - (yy * aa);
+
+	return (zz < 0 ? -1 : (zz == 0 ? 0 : 1));
+}
+
 Circle Geometry::FindCircleForThreePoints(Point p1, Point p2, Point p3)
 {
 	// We use matrices and determinants to find the center and radius of the
@@ -582,6 +597,27 @@ Circle Geometry::FindCircleForThreePoints(Point p1, Point p2, Point p3)
 	return c;
 }
 
+Arc Geometry::FindArcForThreePoints(Point p1, Point p2, Point p3)
+{
+	int orientation = Orientation(p1, p2, p3);
+
+	// Sanity check: if points are colinear, there is no arc
+	if (orientation == 0)
+		return Arc();
+
+	Circle c = FindCircleForThreePoints(p1, p2, p3);
+	double a1 = Vector::Angle(c.p[0], p1);
+	double a2 = Vector::Angle(c.p[0], p2);
+	double span = a2 - a1;
+
+	if (orientation < 0 && span > 0)
+		span -= TAU;
+	else if (orientation > 0 && span < 0)
+		span += TAU;
+
+	return Arc(c.p[0], c.radius[0], a1, span);
+}
+
 double Geometry::Determinant3x3(double a11, double a12, double a13, double a21, double a22, double a23, double a31, double a32, double a33)
 {
 	return (a11 * ((a22 * a33) - (a32 * a23)))
@@ -602,7 +638,6 @@ Arc Geometry::Unpack(Point tail, Point head, double bump)
 
 	// N.B.: The radius can also be found with r = (a² + h²) / 2h where a is
 	// the 1/2 length of the line segment and h is the bump length.
-//	double radius = (length + (1.0 / length)) / 2.0;
 	double radius = 0.5 * (((length * length) + (bumpLen * bumpLen)) / bumpLen);
 	Vector ctrVec = mpNormal * (radius - bumpLen);
 	Point center = midpoint + ctrVec;
@@ -621,3 +656,19 @@ Arc Geometry::Unpack(Point tail, Point head, double bump)
 
 	return Arc(center, radius, angle1, span);
 }
+
+double Geometry::Pack(Arc * a)
+{
+	Point p1 = a->p[0] + (Vector(cos(a->angle[0]), sin(a->angle[0])) * a->radius[0]);
+	Point p2 = a->p[0] + (Vector(cos(a->angle[0] + a->angle[1]), sin(a->angle[0] + a->angle[1])) * a->radius[0]);
+	double endpointLen = Vector::Magnitude(p1, p2) / 2.0;
+
+	// Bump height can be found with h = r ± sqr(r² - a²) where r is the
+	// radius, and a is the 1/2 length of the endpoint's line segment.  The
+	// plus/minus term is positive if the arc span is less than 1/2 TAU,
+	// negative if the arc span is greater than 1/2 TAU.
+	double discriminant = sqrt((a->radius[0] * a->radius[0]) - (endpointLen * endpointLen));
+	double bumpLen = a->radius[0] + (discriminant * (fabs(a->angle[1]) < HALF_TAU ? 1.0 : -1.0));
+
+	return (bumpLen / endpointLen) * (a->angle[1] > 0 ? -1.0 : 1.0);
+}