Question about distance of a point to a segment

Question

The following code uses Line2D.ptSegDist in order to find the closest distance of each point from (0, 0), (0, 1)... to (100, 100). If the distance returned from the method is r (0), then the 1x1 rectangle being drawn is white, but the line drawn in the loops is dotted and not like the one drawn by the Graphics.drawLine method. The line is drawn correctly when r's value is changed to 0.5, but I do not believe that that is the proper way to handle the value returned, because if the line is diagonal (0, 0, 10, 10), then r can remain as 0. My goal is to test to see if a point is contained on a given line. I can achieve this by using the Bresenham line algorithm, but I was wondering if it's possible to do it using the Line2D.ptSegDist method, and if so, how could I go about doing this?
import java.awt.Color;
import java.awt.Graphics;
import java.awt.geom.Line2D;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class PtSegDistTest extends JPanel {
    private final double x1 = 9;
    private final double y1 = 22;
    private final double x2 = 19;
    private final double y2 = 92;
    private final double r = 0.0;
    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        for (int i = 0; i < 100; i++) {
            for (int j = 0; j < 100; j++) {
                g.setColor(Line2D.ptSegDist(x1, y1, x2, y2, i, j) <= r
                        ? Color.WHITE : Color.BLACK);
                g.fillRect(i, j, 1, 1);
        g.setColor(Color.WHITE);
        g.drawLine((int) x1 + 10, (int) y1, (int) x2 + 10, (int) y2);
    public static void main(String[] args) {
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(new PtSegDistTest());
        f.setSize(250, 250);
        f.setVisible(true);
}Thank you for your help.

Answer 1

Thank you for helping me to understand. I was hoping that I could use the method in order to test to see if a point was on the line by using the distance method. The Bresenham line algorithm works fine, but do you know of any other way (just out of curiosity) that doesn't involve going through each individual point on the line that would achieve similar results?
What I'm trying to do is take two arbitrary points with a distance of 15, and see if any other arbitrary points fall between that line. I've found that the margin for "pixels sufficiently close to the line" is 0.5 (as noted above), but when I use this margin, some different points appear and are missing in comparison to the Bresenham line algorithm
Edited by: batj on May 16, 2010 6:23 AM