/**
 * Returns whether a circle is within view of an object at the origin 
 * facing some direction.
 * 
 * @param origin
 * 	The origin of the view.
 * @param direction
 * 	The direction of the view, must be a normalized vector.
 * @param fov
 * 	The vector where x=cos(FOV/2) and y=sin(FOV/2), must be normalized by definition.
 * @param circle
 * 	The center of the circle.
 * @param radius
 * 	The radius of the circle.
 * @param entirely
 * 	True if this method should return whether the circle is completely 
 * 	within view, or false if this method should return whether the circle 
 * 	is partially within view.
 * @return
 * 	True if the target is in view, otherwise false.
 */
public static boolean isCircleInView( Vector origin, Vector direction, Vector fov, Vector circle, float radius, boolean entirely )
{
	// Calculate upper and lower vectors
	// Calculate forward vector between target and origin
	// Rotate forward by upper, resulting vector.y is the distance from upper to target
	// Rotate forward by lower, resulting vector.y is the distance from lower to target
	// If it doesn't matter if it's entirely in view, add radius*2 to the distances.
	
	float fovy = Math.abs( fov.y );
	float dxfx = direction.x * fov.x;
	float dxfy = direction.x * fovy;
	float dyfx = direction.y * fov.x;
	float dyfy = direction.y * fovy;
	float upperX = (dxfx - dyfy);
	float upperY = (dxfy + dyfx);
	float lowerX = (dxfx + dyfy);
	float lowerY = (dyfx - dxfy);
	float forwardX = circle.x - origin.x;
	float forwardY = circle.y - origin.y;
	float upperDist = (upperX * forwardY + upperY * forwardX);
	float lowerDist =-(lowerX * forwardY + lowerY * forwardX);
	
	if (!entirely)
	{
		upperDist += radius * 2;
		lowerDist += radius * 2;
	}
	
	return (lowerDist >= radius && upperDist >= radius) || // FOV <= 90
			 (fov.x < 0 && (upperDist >= radius || lowerDist >= radius)); // FOV >= 90
}