在两个节点（圆）之间绘制一条边（线）

Question

I am working on a dependancy graph that consists of multiple nodes and multiple directed edges from one node to another in the graph.

I am trying to draw a visualation of the graph by adding n number of nodes as circles and edges between those nodes as a line.

I a using Graphics library of Java along with JPanel and Jframe.

This is currently the code I have made:

public class LoopUnrolling extends JPanel{


static int length = 5;
static String graph[][] = new String[length][length];


@Override
public void paintComponent(Graphics g){

    super.paintComponent(g);

    Random random = new Random();

    int x1 = random.nextInt(500);
    int y1 = random.nextInt(100);

    int x2 = random.nextInt(500);
    int y2 = random.nextInt(100);

    g.setColor(Color.red);
    g.drawOval(x1,y1,30,40);
    g.drawOval(x2,y2,30,40);
    g.drawLine(x1, y1, x2, y2);



}
public static void main(String[] args) {

         LoopUnrolling paintObject = new LoopUnrolling();
         JFrame jf = new JFrame();
         jf.setTitle("Dependancy Graph");
         jf.setSize(600,400);
         jf.setVisible(true);
         jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
         jf.add(paintObject);
        }


 }

I was able to draw two circles and a line but the problem I am getting is connecting those two circles with an edge.

I have drawn each node at a random place on the canvas and want to add a Line between those two nodes. The line has Point1(x1,y1) and Point2(x2,y2). These points should be the points on two different Node's(Circles) outline

Answer 1

You have two ellipses with centers

 cx1 = x1 + w1/2, cy1 = y1 + h1/2 
 and 
 cx2 = x2 + w2/2, cy2 = y2 + h2/2 

where wxx and hxx are width and height of ellipse (third and fourth parameters of drawOval )

Get difference vector

 dx = cx2 - cx1
 dy = cy2 - cy1

Normalize it

 len  = sqrt(dx*dx + dy*dy)
 dx = dx / len
 dy = dy / len

Now calculate points at circumference

 r1 = 0.5 * w1 * h1 / sqrt(w1*w1*dy*dy+h1*h1*dx*dx)
 px1 = cx1 + r1 * dx
 py1 = cy1 + r1 * dy

 r2 = 0.5 * w2 * h2 / sqrt(w2*w2*dy*dy+h2*h2*dx*dx)
 px2 = cx2 - r2 * dx
 py2 = cy2 - r2 * dy

And draw line segment (px1,py1)-(px2,py2)

Sample Delphi implementation and result: