regarding draw a graph with zoom speciality

[karthik tvn]

Hi to all,

i have a text file which contains the x,y coordinates of the sinewave.Using these coordinates i need to draw the sinewave graph.Then,i need an option in graph to zoom in and zoom out the graph.How should i do this? kindly post any ideas,if any open source is available please provide me link.

[Ulf Dittmer]

Welcome to JavaRanch.

The Code Barn contains sample code to draw both X/Y graph and a sine curve.

What ideas have you had for implementing the zoom?

[karthik tvn]

thanks for your information. i did draw a xy graph.But i want the coordinates are should be taken from file called as sinewave.txt file.

i dont know about zoom operation.

[Ulf Dittmer]

Do you know how to use the java.io package to read data from a file?

As for zooming, let's say the image is centered on point (x0, y0), has a width of w and a height of h (in terms of the data displayed, not screen coordinates). Zooming in would mean that w and h get smaller by some factor f.

So instead of drawing x coordinates from x0-w/2 to x0+w/2 and y coordinates from y0-h2/ to y0+h/2, you would draw from x0-w/(2*f) to x0+w/(2*f) and y coordinates from y0-h/(2*f) to y0+h/(2*f). f might be in the order of 1.5 (or maybe sqrt(2) ) for each zoom step. Does this help?

[Campbell Ritchie]

Would the scale method of Graphics2D be of any use, do you think, Ulf?

[Ulf Dittmer]

Would the scale method of Graphics2D be of any use

Not without preceding and subsequent translate method calls, in which case we're into using affine transformations (which may or may not be something the OP is familiar with).
[ February 17, 2008: Message edited by: Ulf Dittmer ]

[Craig Wood]

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import javax.swing.*;
 
public class ZoomGraph extends JPanel implements ActionListener {
    Path2D.Double sineWave;
    AffineTransform at = new AffineTransform();
    double scale = 1.0;
    double scaleInc = 0.01;
 
    public void actionPerformed(ActionEvent e) {
        String ac = e.getActionCommand();
        if(ac.equals("ZOOM IN"))
            scale += scaleInc;
        else if(scale > 0.25)
            scale -= scaleInc;
        setTransform();
        repaint();
    }
 
    private void setTransform() {
        double x = (1.0 - scale)*getWidth()/2.0;
        double y = (1.0 - scale)*getHeight()/2.0;
        at.setToTranslation(x, y);
        at.scale(scale, scale);
    }
 
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        g2.setRenderingHint(RenderingHints.KEY_STROKE_CONTROL,
                            RenderingHints.VALUE_STROKE_PURE);
        if(sineWave == null)
            initWave();
        g2.setPaint(Color.blue);
        Shape s = at.createTransformedShape(sineWave);
        g2.draw(s);
    }
 
    /** taken from [url=http://faq.javaranch.com/java/PlotSineCurve]http://faq.javaranch.com/java/PlotSineCurve[/url] */
    private void initWave() {
        int w = getWidth();
        int h = getHeight();
        sineWave = new Path2D.Double();
        for(int x = 0; x < w; x++) {
            double y = h/2.0 - Math.sin(((double)x/w)*2*Math.PI)*(h-2)/2.0;
            if(x > 0)
                sineWave.lineTo(x, y);
            else
                sineWave.moveTo(x, y);
        }
    }
 
    private JPanel getControls() {
        String[] ids = { "zoom in", "zoom out" };
        JPanel panel = new JPanel();
        for(int j =- 0; j < ids.length; j++) {
            JButton button = new JButton(ids[j]);
            button.setActionCommand(ids[j].toUpperCase());
            button.addActionListener(this);
            panel.add(button);
        }
        return panel;
    }
 
    public static void main(String[] args) {
        ZoomGraph test = new ZoomGraph();
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(test);
        f.add(test.getControls(), "Last");
        f.setSize(400,400);
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }
}

[Campbell Ritchie]

Originally posted by Ulf Dittmer:

Not without preceding and subsequent translate method calls, in which case we're into using affine transformations (which may or may not be something the OP is familiar with).

Agree. AffineTransforms count as bravery beyond the call of duty.