Collisions / Intersections

Collisions are important in games. Java has a simple built in collision method that detects if two rectangles collide (ie. intersect). There is nothing for any other shape.

We want to write a program to determine if a line and a circle intersect.
You can download and run my program to see how it looks: CircleLineIntersect.jar. Windows: click on the jar file to run it. Linux (and Mac?) in a terminal type "java -jar CircleLineIntersect"

What to do:

• Make a cicle on the screen that is draggable
• Make a line on the screen that is draggable. I use <shift>-drag to move the left end of the line and <control>-drag to move the right end.
• Now calculate if the line touches the circle.
  There are some simple cases we can check first:
  1. Is the circle far from the line (beyond the radius + half the length of the line)
  2. Is the endpoint of the line in the circle?
• Other than these two, we have to actually calculate if the line touches the circle. This will involve knowlege of geometry and algebra.

Please colour code the background so that it shows which situation the line and circle are in.

NOTE: to start with you can just hardcode the coordinates of the circle and line. Later on you can make them draggable.

DrawingPanel panel;
Circle circle;
Point l1, l2;
[...]

circle = new Circle(270,250,100);
l1 = new Point(150,150);
l2 = new Point(600,200);
[...]

class Circle {
	int x,y,r;
	
	Circle(int x, int y, int r) {			
		this.x = x;
		this.y = y;
		this.r = Math.abs(r); //negative radii not allowed
	}
	
	void paint(Graphics2D g2) {
		g2.setColor(Color.BLACK);
		g2.drawOval(x-r, y-r, r+r, r+r);
	}
}