advice on drawing a square wave pulse train

[Nikos Stavros]

I want to draw graphicaly a square wave pulse train. This will work by users pressing on a canvas and the x coord generating a toggle point (high or low switch). Can anyone reccomend any java packages or external packages where this could be done or will I have to create my own package.

[Craig Wood]

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import javax.swing.*;
 
public class SquareWave
{
    public static void main(String[] args)
    {
        SquareWave squareWave = new SquareWave();
        SquareWavePanel squareWavePanel = new SquareWavePanel();
        WaveMaker waveMaker = new WaveMaker(squareWavePanel);
        squareWavePanel.addMouseListener(waveMaker);
        JFrame f = new JFrame("click to make wave");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(squareWavePanel);
        f.getContentPane().add(squareWave.getControls(waveMaker), "South");
        f.setSize(500,300);
        f.setLocation(200,200);
        f.setVisible(true);
    }
 
    private JPanel getControls(final WaveMaker waveMaker)
    {
        final JButton start = new JButton("start");
        final JButton stop  = new JButton("stop");
        ActionListener l = new ActionListener()
        {
            public void actionPerformed(ActionEvent e)
            {
                JButton button = (JButton)e.getSource();
                if(button == start)
                    waveMaker.start();
                if(button == stop)
                    waveMaker.stop();
            }
        };
        start.addActionListener(l);
        stop.addActionListener(l);
        JPanel panel = new JPanel();
        panel.add(start);
        panel.add(stop);
        return panel;
    }
}
 
class SquareWavePanel extends JPanel
{
    GeneralPath wave = new GeneralPath();
    double waveX = 0.0;
    float width;
    double waveLength;
    final int deltaX = -2;  // direction is right to left
 
    protected void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        int w = getWidth();
        int h = getHeight();
        g2.setPaint(new Color(240, 220, 220));
        g2.draw(new Line2D.Double(w/2, 0, w/2, h));
        g2.draw(new Line2D.Double(0, h/2, w, h/2));
        g2.setPaint(Color.blue);
        AffineTransform at = AffineTransform.getTranslateInstance(waveX, 0.0);
        g2.draw(at.createTransformedShape(wave));
        // keep wave continuous as it passes through the view
        if(waveX + waveLength <= w + width)
        {
            double dx = waveX + waveLength - width;
            at.setToTranslation(dx, 0.0);
            g2.draw(at.createTransformedShape(wave));
        }
    }
 
    public void advance()
    {
        waveX += deltaX;
        if(waveX + waveLength <= width)
            waveX += waveLength - width;
        repaint();
    }
 
    /**
     * width and height of wave are determined by the
     * location of the mouse point relative to the
     * center of the view
     */
    protected void setWave(Point p)
    {
        int w = getWidth();
        int h = getHeight();
        // set width and height relative to center
        width = 2 * Math.abs(w/2 - p.x);
        // avoid small periods/high wave cycles
        if(width < 30.0f)
            width = 30.0f;
        float height = p.y - h/2;
        // start at far left of view
        waveX = 0.0f;
        float posX = 0;
        float posY = h/2 + height;
        // build the wave
        wave.reset();
        wave.moveTo(posX, posY);
        posX += width;
        wave.lineTo(posX, posY);
        // continue to fill the view
        while(posX < w)
        {
            posY = h/2 - height;
            wave.lineTo(posX, posY);
            posX += width;
            wave.lineTo(posX, posY);
            posY = h/2 + height;
            wave.lineTo(posX, posY);
            posX += width;
            wave.lineTo(posX, posY);
        }
        // save the length of the wave
        waveLength = posX;
        repaint();
    }
}
 
class WaveMaker extends MouseAdapter implements Runnable
{
    SquareWavePanel squareWavePanel;
    Thread thread;
    boolean animate;
    final int delay = 25;
 
    public WaveMaker(SquareWavePanel swp)
    {
        squareWavePanel = swp;
        animate = false;
    }
 
    public void start()
    {
        if(!animate)
        {
            animate = true;
            thread = new Thread(this);
            thread.setPriority(Thread.NORM_PRIORITY);
            thread.start();
        }
    }
 
    public void stop()
    {
        animate = false;
        thread = null;
    }
 
    public void run()
    {
        while(animate)
        {
            squareWavePanel.advance();
            try
            {
                Thread.sleep(delay);
            }
            catch(InterruptedException ie)
            {
                System.err.println("interrupt: " + ie.getMessage());
                animate = false;
            }
        }
    }
 
    public void mousePressed(MouseEvent e)
    {
        Point p = e.getPoint();
        squareWavePanel.setWave(p);
    }
}

[Nikos Stavros]

Thanks for that, very nice. I can see me using some of that code

[Nikos Stavros]

BTW how long did it take you to write that?

[Nikos Stavros]

As a continuation, I would like to have a stationary pulse train that is around 200 * 30000 pixels long. Obviously I will need some sort of scrollbar in my graphics window to move beetween different points in the pulse train, but I am not sure how to go about this as it seems complex.

An idea was to only display the coords in the range offset determined by the scrollbar cursor position.

Any pointers to code that does this sort of thing?

cheers

[Craig Wood]

how long did it take you to write that
I didn't notice
will need some sort of scrollbar in my graphics window
Setting the preferred size of the component will take care of this. The parent JScrollPane asks for this Dimension when it is ready to set its scrollbars for display of its child component/view.
display the coords in the range offset determined by the scrollbar cursor position
Java clips the graphics context so our custom graphics are drawn only on the visible area.

import java.awt.*;
import java.awt.geom.GeneralPath;
import javax.swing.*;
 
public class StandingWave extends JPanel
{
    GeneralPath wave;
 
    public StandingWave()
    {
        Dimension d = getPreferredSize();
        d.width = 30000;
        setPreferredSize(d);
    }
 
    protected void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        if(wave == null)
            initWave();
        g2.setPaint(Color.blue);
        g2.draw(wave);
    }
 
    private void initWave()
    {
        float w = getWidth();
        float h = getHeight();
        // totalWidth = steps * 2 * dx
        // dx = totalWidth/2*steps
        // for dx ~= 100
        float approxCycles = w/(2*100);
        // calculate dx to just fit wave into totalWidth (w-1)
        float dx = (w-1)/(int)Math.round(2*approxCycles);
        float dy = h/4;      // 100 for a wave height of 200
        float step = 2*dx;
        int steps = (int)(w/step);
        wave = new GeneralPath();
        float x = 0, y = h/2;
        wave.moveTo(x,y);
        for(int j = 0; j < steps; j++)
        {
            wave.lineTo(x,y-dy);
            x += dx;
            wave.lineTo(x,y-dy);
            wave.lineTo(x,y+dy);
            x += dx;
            wave.lineTo(x,y+dy);
            wave.lineTo(x,y);
        }
        // check fit
        //float total = steps*2*dx;
        //System.out.printf("steps = %d\nw-total = %.1f\n", steps, w-total);
    }
 
    public static void main(String[] args)
    {
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(new JScrollPane(new StandingWave()));
        f.setSize(500,400);
        f.setLocation(200,200);
        f.setVisible(true);
    }
}

[Nikos Stavros]

Thats exactly what I needed,

craig thanks again

[Nikos Stavros]

I want to add more functionality to this, however when I want to set the content pane to have a flowlayout, it distorts things and the scroll bars disappear completely

  public static void main(String[] args)
    {
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().setLayout(new FlowLayout());
        f.getContentPane().add(new JScrollPane(new StandingWave()));
       // f.getContentPane().add(zoomOut);
        f.setSize(500,400);
        f.setLocation(200,200);
        f.setVisible(true);
    }  

[Craig Wood]

FlowLayout is not a good choice for this. You can add components to the other sections of the JFrames default BorderLayout (north, west, east and south). Or you can assemble the graphic component (StandingWave) with other components and add them to the center section of the layout. Making friends with the layout managers takes some patience and practice. For more information there is Lesson: Laying Out Components Within a Container with links to some useful pages:
1 — A Visual Guide to Layout Managers
2 — Using Layout Managers
3 — How to...
I added the graphic component to the center of the BorderLayout which expands it in both directions to fill the available space. Therefore I did not have to provide any size hints beyond the width (30000) which I set in the preferredSize. These little tricks come with practice and experimentation. A Flowlayout will show the component at its preferredSize which is the default height (10, I didn't change this) and the width of 30000. Another peculiarity of FlowLayout is that it does not calculate the size of components that are not visible; it reports only the size of the visible (portion of the) components in the gui. So the JScrollPane doesn't get the correct information it needs to properly display the component.

[Nikos Stavros]

Ah , the BorderLayout is the containers defult layout, interesting

[Nikos Stavros]

In the following code I only have one Jscrollpane appearing

  public class Controller {
 
public Controller(){
JFrame f = new JFrame();
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    Container contentPane = f.getContentPane();
    contentPane.setLayout(new GridLayout(2,1));
    //int parameter is unimportant
    contentPane.add(new JScrollPane(new StandingWave(1)));
    contentPane.add(new JScrollPane(new StandingWave(1)));
etc
etc  

[Nikos Stavros]

I managed to solve it by doing this,

   public class Controller {
 
public Controller(){
JFrame f = new JFrame();
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    Container contentPane = f.getContentPane();
    JPanel p = new JPanel();
    contentPane.add(p);
    
    p.setLayout(new GridLayout(2,1));
    //int parameter is unimportant
    p.add(new JScrollPane(new StandingWave(1)));
    p.add(new JScrollPane(new StandingWave(1))); 

[Craig Wood]

In the following code I only have one Jscrollpane appearing
Look at the second paragraph in the discussion section of the BorderLayout api: using no constraint defaults to the center section (BorderLayout.CENTER = "Center").
The first JScrollPane is removed from the center section and the second one is added.