Slick Forums

   /**
    * Check if circle contains the line
    * @param line Line to check against
    * @return True if line inside circle
    */
   private boolean contains(Line line) {
        return contains(line.getX1(), line.getY1()) && contains(line.getX2(), line.getY2());
   }

    /**
     * Check if circle touches a line.
     * @param other The line to check against
     * @return True if they touch
     */
    private boolean intersects(Line other) {
        // put it nicely into vectors
        Vector2f lineSegmentStart = new Vector2f(other.getX1(), other.getY1());
        Vector2f lineSegmentEnd = new Vector2f(other.getX2(), other.getY2());
        Vector2f circleCenter = new Vector2f(getCenterX(), getCenterY());

        // calculate point on line closest to the circle center and then
        // compare radius to distance to the point for intersection result
        Vector2f closest;
        Vector2f segv = lineSegmentEnd.copy().sub(lineSegmentStart);
        Vector2f ptv = circleCenter.copy().sub(lineSegmentStart);
        float segvLength = segv.length();
        float projvl = ptv.dot(segv) / segvLength;
        if (projvl < 0)
        {
            closest = lineSegmentStart;
        }
        else if (projvl > segvLength)
        {
            closest = lineSegmentEnd;
        }
        else
        {
            Vector2f projv = segv.copy().scale(projvl / segvLength);
            closest = lineSegmentStart.copy().add(projv);
        }
        boolean intersects = circleCenter.copy().sub(closest).lengthSquared() <= getRadius()*getRadius();
       
        return intersects;
    }
}

   public boolean intersects(Shape shape)
    {
        if (shape instanceof Circle)
        {
            return shape.intersects(this);
        }
        return super.intersects(shape);
    }