added new helper methods

worked on gridWalker v3

geo/Circle2.h

@@ -5,6 +5,7 @@
 
 #include "Point2.h"
 #include "Ray2.h"
+#include "Line2.h"
 
 #include "../Assertions.h"
 
@@ -65,6 +66,24 @@ public:
 
 	}
 
+	/** does this circle intersect with the given ray? */
+	bool intersects(const Line2 line) const {
+
+		// https://math.stackexchange.com/questions/311921/get-location-of-vector-circle-intersection
+		Point2 dir = line.p2 - line.p1;
+		Point2 start = line.p1;
+		const float a = dir.x*dir.x + dir.y*dir.y;
+		const float b = 2 * dir.x * (start.x-center.x) + 2 * dir.y * (start.y - center.y);
+		const float c = (start.x-center.x) * (start.x-center.x) + (start.y - center.y)*(start.y - center.y) - radius*radius;
+		const float discr = b*b - 4*a*c;
+
+		if (discr < 0) {return false;}
+
+		const float t = (2*c) / (-b + std::sqrt(discr));
+		return (t <= 1) && (t >= 0);
+
+	}
+
 
 	/** configure this sphere to contain the given point-set */
 	void adjustToPointSet(const std::vector<Point2>& lst) {