X-Git-Url: http://shamusworld.gotdns.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=src%2Fgeometry.cpp;h=95d12c65068b16715086191e1d70c7e01483dcbd;hb=bf5a50feb0f84a4627a65c5b82c3ca2d2eefe54b;hp=b9158974ec97d902d4ff2e936a2cc4b43e469082;hpb=0fcc2d879e1e0ca17eeaceae2159f5143a06586f;p=architektonas

diff --git a/src/geometry.cpp b/src/geometry.cpp
index b915897..95d12c6 100644
--- a/src/geometry.cpp
+++ b/src/geometry.cpp
@@ -39,6 +39,29 @@ double Geometry::ParameterOfLineAndPoint(Point tail, Point head, Point point)
 }
 
 
+double Geometry::DistanceToLineFromPoint(Point tail, Point head, Point point)
+{
+	// Interpretation: given a line in the form x = a + tu, where u is the
+	// unit vector of the line, a is the tail and t is a parameter which
+	// describes the line, the distance of a point p to the line is given by:
+	// || (a - p) - ((a - p) . u) u ||
+	// We go an extra step: we set the sign to reflect which side of the line
+	// it's on (+ == to the left if head points away from you, - == to the
+	// right)
+	Vector line(tail, head);
+	Vector u = line.Unit();
+	Vector a_p = tail - point;
+	Vector dist = a_p - (u * (a_p).Dot(u));
+
+	double angle = Vector::Angle(tail, point) - line.Angle();
+
+	if (angle < 0)
+		angle += TAU;
+
+	return dist.Magnitude() * (angle < HALF_TAU ? +1.0 : -1.0);
+}
+
+
 Point Geometry::MirrorPointAroundLine(Point point, Point tail, Point head)
 {
 	// Get the vector of the intersection of the line and the normal on the
@@ -255,14 +278,12 @@ void Geometry::CheckLineToCircleIntersection(Object * l, Object * c)
 	// Radius is the hypotenuse, so we have to use c² = a² + b² => a² = c² - b²
 	double perpendicularLength = sqrt((c->radius[0] * c->radius[0]) - (distance * distance));
 
-	// Now, find the points using the length, then check to see if they are on
-	// the line segment
+	// Now, find the intersection points using the length...
 	Vector lineUnit = Vector(l->p[0], l->p[1]).Unit();
 	Point i1 = p + (lineUnit * perpendicularLength);
 	Point i2 = p - (lineUnit * perpendicularLength);
 
-	// Now we have our intersection points, next we need to see if they are on
-	// the line segment...
+	// Next we need to see if they are on the line segment...
 	double u = ParameterOfLineAndPoint(l->p[0], l->p[1], i1);
 	double v = ParameterOfLineAndPoint(l->p[0], l->p[1], i2);
 
@@ -342,3 +363,22 @@ Point Geometry::GetPointForParameter(Object * obj, double t)
 	return Point(0, 0);
 }
 
+
+Point Geometry::Midpoint(Line * line)
+{
+	return Point((line->p[0].x + line->p[1].x) / 2.0,
+		(line->p[0].y + line->p[1].y) / 2.0);
+}
+
+
+/*
+How to find the tangent of a point off a circle:
+
+ •  Calculate the midpoint on the point and the center of the circle
+ •  Get the length of the line segment from the and the center divided by two
+ •  Use that length to construct a circle with the point at the center and the
+    radius equal to that length
+ •  The intersection of the two circles are the tangent points
+
+*/
+