How to draw custom components on a resizeable JPanel with a specific coordinate system?

Question

I'm working on a graph-tree visualizing application. The program could create different layouts for visualizing trees. By tree I mean a Node object which could have a Node as a parent, and a list of nodes called children. By creating layout for a tree, I mean setting an X and a Y coordinate of each node of the tree. There are multiple layout algorithms all of them are in an implementation of a LayoutAlgorithm interface, and one of their methods takes a root node (the one node of the tree without a parent), and calculating the X and Y coordinate for each node of the tree.

To visualize these layouts, I could use a JPanel, and tell exactly in which coordinate I'd like to draw my nodes, and after, I could draw lines between them. Thats a bit problemmatic, because, I'd like to draw a node with x=0 and y=0 coordinates to the left side horizontally and to the middle vertically. To achieve that, I could simply offset the y-coordinates of each node, and draw them after, but I'd want the JPanel to be resizable. Thats also achivable by redrawing each of the nodes after a resize operation happened. But thats too much complexity, so Im wondering if there is an easier/simpler solution for that, like a custom LayoutManager for the JPanel.

I've tried several LayoutManager, but none of them are letting me put JComponents on the panel using coordinates.

Answer 1

By creating a custom JComponent class and overriding the paint method, its possible to offset the coordinates of the components and graphics to be drawn, by calling the g.translate(...) method.

import javax.swing.*;
import java.awt.*;

public class VerticallyAlignedJPanel extends JPanel {

    public VerticallyAlignedJPanel() {
        super();
        setLayout(null);
    }

    @Override
    protected void paintComponent(Graphics g) {
        g.translate(0, getHeight()/2);
        super.paintComponent(g);
    }
}