X-Git-Url: http://shamusworld.gotdns.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=src%2Fvector.cpp;h=57f49fbb8b1d4bc7ae1566c91cdb58586691895f;hb=742d2aa9bb46bce4f690474fa22f5980e175e55e;hp=11ddb6494962b724e8166b05502baa27612c0295;hpb=fd5a80446b2abfdfb9d8951fcc03fb1b55ad707c;p=architektonas

diff --git a/src/vector.cpp b/src/vector.cpp
index 11ddb64..57f49fb 100644
--- a/src/vector.cpp
+++ b/src/vector.cpp
@@ -31,6 +31,15 @@ Vector::Vector(Vector tail, Vector head): x(head.x - tail.x), y(head.y - tail.y)
 }
 
 
+// Create vector from angle + length (2D; z is set to zero)
+void Vector::SetAngleAndLength(double angle, double length)
+{
+	x = cos(angle) * length;
+	y = sin(angle) * length;
+	z = 0;
+}
+
+
 Vector Vector::operator=(Vector const v)
 {
 	x = v.x, y = v.y, z = v.z;
@@ -185,7 +194,8 @@ Vector Vector::Unit(void)
 {
 	double mag = Magnitude();
 
-	// If the magnitude of the vector is zero, then the Unit vector is undefined...
+	// If the magnitude of the vector is zero, then the Unit vector is
+	// undefined...
 	if (mag == 0)
 		return Vector(0, 0, 0);
 
@@ -195,17 +205,17 @@ Vector Vector::Unit(void)
 
 double Vector::Magnitude(void)
 {
-	return sqrt(x * x + y * y + z * z);
+	return sqrt((x * x) + (y * y) + (z * z));
 }
 
 
 double Vector::Angle(void)
 {
-	// acos returns a value between zero and PI, which means we don't know which
-	// quadrant the angle is in... Though, if the y-coordinate of the vector is
-	// negative, that means that the angle is in quadrants III - IV.
+	// acos returns a value between zero and TAU/2, which means we don't know
+	// which quadrant the angle is in... However, if the y-coordinate of the
+	// vector is negative, that means that the angle is in quadrants III - IV.
 	double rawAngle = acos(Unit().x);
-	double correctedAngle = (y < 0 ? (2.0 * PI) - rawAngle : rawAngle);
+	double correctedAngle = (y < 0 ? TAU - rawAngle : rawAngle);
 
 	return correctedAngle;
 }
@@ -219,13 +229,13 @@ bool Vector::isZero(double epsilon/*= 1e-6*/)
 
 // Class methods
 
-double Vector::Dot(Vector v1, Vector v2)
+/*static*/ double Vector::Dot(Vector v1, Vector v2)
 {
 	return (v1.x * v2.x) + (v1.y * v2.y) + (v1.z * v2.z);
 }
 
 
-double Vector::Magnitude(Vector v1, Vector v2)
+/*static*/ double Vector::Magnitude(Vector v1, Vector v2)
 {
 	double xx = v1.x - v2.x;
 	double yy = v1.y - v2.y;
@@ -234,10 +244,19 @@ double Vector::Magnitude(Vector v1, Vector v2)
 }
 
 
+//
+// Convenience function
+//
+/*static*/ double Vector::Angle(Point p1, Point p2)
+{
+	return Vector(p1, p2).Angle();
+}
+
+
 // Returns the parameter of a point in space to this vector. If the parameter
 // is between 0 and 1, the normal of the vector to the point is on the vector.
 // Note: v1 is the tail, v2 is the head of the line (vector).
-double Vector::Parameter(Vector tail, Vector head, Vector p)
+/*static*/ double Vector::Parameter(Vector tail, Vector head, Vector p)
 {
 	// Geometric interpretation:
 	// The parameterized point on the vector lineSegment is where the normal of
@@ -253,15 +272,27 @@ double Vector::Parameter(Vector tail, Vector head, Vector p)
 }
 
 
-// Return the normal to the linesegment formed by the passed in points.
-// (Not sure which is head or tail, or which hand the normal lies)
-// [v1 should be the tail, v2 should be the head, in which case the normal should
-//  rotate anti-clockwise.]
-///*static*/ Vector Vector::Normal(Vector v1, Vector v2)
+// Return the 2D normal to the linesegment formed by the passed in points.
+// The normal thus calculated should rotate anti-clockwise.
 /*static*/ Vector Vector::Normal(Vector tail, Vector head)
 {
-//	Vector v = (v1 - v2).Unit();
 	Vector v = (head - tail).Unit();
 	return Vector(-v.y, v.x);
 }
 
+
+/*static*/ double Vector::AngleBetween(Vector a, Vector b)
+{
+	// This is done using the following formula:
+	// (a . b) = ||a|| ||b|| cos(theta)
+	// However, have to check for two degenerate cases, where a = cb:
+	// 1) if c > 0, theta = 0; 2) if c < 0, theta = 180°.
+	// Also, the vectors a & b have to be non-zero.
+	// Also, have to check using an epsilon because acos will not return an
+	// exact value if the vectors are orthogonal.
+	if (a.isZero() || b.isZero())
+		return 0;
+
+	return acos(a.Dot(b) / (a.Magnitude() * b.Magnitude()));
+}
+