Java2D drawRect()

[Tian Zhang]

Hi there!

I am just getting started with Java2D (more accurately, "restarted" after an 8 year break from Java ) and have hit an interesting behaviour when playing with Java2D. Here is the code in question:

public class Renderer extends JPanel {

    public Renderer() {}

    @Override
    public void paintComponent(Graphics graphics) {
        super.paintComponent(graphics);

        Graphics2D g2d = (Graphics2D) graphics;

        g2d.setStroke(new BasicStroke());
        g2d.drawRect(100, 100, 10, 10);
    }

    ...
}

The code above should draw an rectangle when the Render is added to a JFrame, however ends up drawing a square with with the bottom edge misaligned (see attachment).

The issue goes away if I force BasicStroke(1.1f), however feel that this is a bit of a hack.

Why does the miss-alignment happen and what is the "best practise fix" for this?


Thanks!
Tian

[Piet Souris]

hi Tian,

I do not see any mis-alignment on my screen. Of course, 10 by 10 is a bit small for my eyes to see
it sharp, but as said, I see nothing wrong. And when I enlarge the rectangle (say 100 x 100 or
200 x 200), and/or use a BasicStroke(7), I see nothing wrong.

If you enlarge your rectangle as well, do you still see this effect?

Greetz,
Piet

[Tian Zhang]

Hello Piet,

The size of the rectangle seems to be irrelevant, and the misalignment does not happen with stroke width > 1. Furthermore the misalignment goes away after resizing the JFrame too...

I've distilled the code down to the following:

import java.awt.Graphics;
import java.awt.Graphics2D;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;


public class Program extends JFrame {
    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                Program program = new Program();
                program.setVisible(true);
            }
        });
    }

    public Program() {
        initialiseUI();
    }

    private void initialiseUI() {
        setSize(400, 300);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationRelativeTo(null);

        add(new JPanel() {
            public void paintComponent(Graphics graphics) {
                super.paintComponent(graphics);

                Graphics2D g2d = (Graphics2D) graphics;
                g2d.drawRect(50, 50, 100, 100);
            }
        });
    }
}

Strangely enough, the code renders fine with jdk1.7.0_67 (see attachment) and the misalignment only seems to happen with jdk1.8.0_20 (see attachment).

(You may need to zoom into the images to see the pixel that's sticking out)

Tian

[Piet Souris]

hi Tian,

indeed, I tested it on jdk1.7.0_25.
On my pc, I have Win XP 32bit, so at the moment I cannot test it on java8.
I'll have a look later this evening, using my wife's laptop.

Greetz,
Piet

[Piet Souris]

hi Tian,

well, I tried it on 1.8_20, but I still see nothing strange here. I ran a loop,
creating lots of rectangles, but they were all perfect. I also tried several
StrokeWidths, again nothing abnormal.

Greetz,
Piet