A few questions about sca

  To: comp.lang.java.gui
I have attached a small program at the end of this post and I have a few
questions about it relating to transforms. It basically draws a rectangle
and two lines within it that intersect in the middle with the rendering
scaling as the dimensions of the window change.

Now, if you run the program change the size of the frame so that it is
either very wide and short or very narrow and tall you will see that the end
points of one of the central lines extend beyond the bounds of the
rectangle.

1. Why is this?
2. At first I thought it was because the line was longer than it should be
as the width of the rectangle is 80 but the line goes from position 0 to 80
so I tried it with a line from 0 to 79. However, then there is a small gap
appearing at certain dimensions between the end of the line and the edge of
the rectangle. Why is there a gap?
3. The most peculiar thing though is that if you resize the frame down to
zero width and height and then resize it to those larger dimensions that
caused the original problem, the problem with the lines extending beyond the
rectangle goes away. Why does it go away?
4. I thought perhaps I need to do some clipping but if you comment out the
setClip() line you will see that some of the thickness of the rectangle's
edges disappears at higher scales. Why is this? I mean if I am using the
rectangle as the clip region, why is part of it being excluded?

Here's the code:

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.geom.AffineTransform;

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

public class TransTest extends JFrame {

    private class MyPanel extends JPanel {

        @Override
        public void paintComponent(final Graphics g) {
            final Graphics2D g2d = (Graphics2D)g;
            final double scaleFactorX = this.getWidth() / 100.0;
            final double scaleFactorY = this.getHeight() / 100.0;
            final AffineTransform at =
                new AffineTransform(AffineTransform.getScaleInstance(scaleFactorX,
scaleFactorY));
            final int width = this.getWidth();
            final int height = this.getHeight();
            final int tx = 10 + (int)((width - 100.0 * scaleFactorX) / 2.0 /
scaleFactorX);
            final int ty = 10 + (int)((height - 100.0 * scaleFactorY) / 2.0 /
scaleFactorY);
            g2d.transform(at);
            g2d.translate(tx, ty);
            final Rectangle r = new Rectangle(0, 0, 80, 80);
            // g2d.setClip(r);
            g2d.draw(r);
            g2d.drawLine(0, 40, 80, 40);
            g2d.drawLine(40, 0, 40, 80);
        }
    }

    public TransTest() {
        this.setLayout(new BorderLayout());
        final MyPanel panel = new MyPanel();
        this.add(panel, BorderLayout.CENTER);
        panel.setBackground(Color.WHITE);
        this.pack();
        this.setSize(500, 520);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setLocationRelativeTo(null);
    }

    public static void main(final String[] args) {
        EventQueue.invokeLater(new Runnable() {

            public void run() {
                new TransTest().setVisible(true);
            }
        });
    }
}

--
And loving it,

-Qu0ll (Rare, not extinct)
_________________________________________________
Qu0llSixFour@gmail.com
[Replace the "SixFour" with numbers to email me]

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