[OT] How to plot a Math.sin() equation

[Adrian Sosialuk]

Hi everyone,

Off topic question - I want to plot a Math.sin() equation
and I got stuck on translation values to real pixel coordinates.
How to scale these values ? Assuming that I have a JPanel
with 300 width and 150 height dimension. What do I need to do ?
Any useful links ?

Thanks,

Adrian

[Jesper de Jong]

Well, the range forthe output values of sin() is -1 to 1. The range of y values in your panel is 0 to 149.

You can simply translate one to the other with a simple addition and multiplication.

1) -1...1 -> 0...2: add 1
2) 0...2 -> 0...149: multiply by 149/2 = 74.5

[Adrian Sosialuk]

Hi Jesper,

Thanks a lot for the tip !

Could you please take a look at this code snippet:

class Sinusoid extends JPanel {
double degToRad(int deg) {
return ((2*3.14)/360)*deg;
}
int scale(int i) {
return (int)((i/300.0)*720.0);
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d=(Graphics2D)g;
for(int i=0;i<300;i++) {
g2d.drawLine(i,(int)Math.round((-Math.sin(degToRad(scale(i)))+1)*100),i,(int)Math.round((-Math.sin(degToRad(scale(i)))+1)*100));
}
}
}

It is supposed to draw a sin(x) for x=-2*pi to x=+2*pi and indeed it does.
The only problem is that I need to resize the window (which is now 300 width
and 200 height) to see the whole graph. I know that some part of the
window is taken by the title bar, so I would have to take it into account
in my calculations. However I wonder why I lack about 10 pixels to see
the graph in full horizontally ? To avoid it, I need to create a window
of size: JFrame(310 instead of 300 ???, 230 instead of 200 because of the title bar).

Thanks,

Adrian

[Jesper de Jong]

I made the following small program to display your sinusoid and it displays fine, I don't need to resize the window to see it:

import java.awt.Dimension;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;
 
public class Main {
    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                JFrame frame = new JFrame("Test");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 
                Sinusoid s = new Sinusoid();
                s.setPreferredSize(new Dimension(300, 200));
                frame.getContentPane().add(s);
 
                frame.pack();
                frame.setVisible(true);
            }
        });
    }
}

[Ulf Dittmer]

I think this code makes a nice example for plotting a function, so I added it as sample code to the FAQ: http://faq.javaranch.com/view?PlotSineCurve. In addition, the plot adapts to the frame size, and optionally a line is drawn connecting the dots.
[ July 09, 2007: Message edited by: Ulf Dittmer ]

[Adrian Sosialuk]

Thanks a lot guys !

PS. Ulf - I think you need to change the comment in your class
from "0 to 2*PI" to "-2*PI to 2*PI"

Cheers,

Adrian

[Ulf Dittmer]

Good catch; thanks.