Java JPanel Scaling

Question

Hey Guys I have succesfully made a GUI in java that will scale polygons and circles using a slider. Everything works but I was wondering if there is a way to change the Origin point(Where it scales from). Right now it scales from the corner and I would like it to scale from the middle so I can start it in the middle and it scales out evenly. Also, If anyone could tell me an easy way to replace the Rectangle I have with an Image of some kind so you can scale the Picture up and down would be great! Thank you! Here is my code:

import javax.swing.*;


public class Fred
{
    public static void main(String[] args)
    {

        TheWindow w = new TheWindow();
        w.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); //X wont close the window with out this line
        w.setSize(375,375);
        w.setVisible(true);
    }

}


import java.awt.*;
import javax.swing.*;
import javax.swing.event.*;


public class TheWindow extends JFrame
{
    private JSlider slider; //declare slider
    private drawRect myPanel; //declare/ create panel


    public TheWindow()
    {
        super("Slider Example"); //make title
        myPanel = new drawRect();
        myPanel.setBackground(Color.green); //change background color

        slider = new JSlider(SwingConstants.VERTICAL, 0, 315, 10);// restrains the slider from scaling square to 0-300 pixels
        slider.setMajorTickSpacing(20); //will set tick marks every 10 pixels
        slider.setPaintTicks(true); //this actually paints the ticks on the screen

        slider.addChangeListener
        (
            new ChangeListener()
            {
                public void stateChanged(ChangeEvent e)
                {
                    myPanel.setD(slider.getValue()); //Wherever you set the slider, it will pass that value and that will paint on the screen
                }
            }

        );

        add(slider, BorderLayout.WEST); //similar to init method, adds slider and panel to GUI
        add(myPanel, BorderLayout.CENTER);


    }






}



import java.awt.*;
import javax.swing.*;

public class drawRect extends JPanel
{

    private int d = 25; //this determines the beginning length of the rect. 

    public void paintComponent(Graphics g)//paints circle on the screen
    {
        super.paintComponent(g); //prepares graphic object for drawing
        g.fillRect(15,15, d, d); //paints rectangle on screen
            //x , y, width, height

    }           

    public void setD(int newD)
    {
        d = (newD >= 0 ? newD : 10); //if number is less than zero it will use 10 for diameter(compressed if statement)
        repaint();

    }

    public Dimension getPrefferedSize()
    {

        return new Dimension(200, 200);     
    }

    public Dimension getMinimumSize()
    {
        return getPrefferedSize();
    }

}

That all comes down to you. *"Origin point"* is contextual to what you want it to mean — MadProgrammer, May 06 '14 at 02:04
Im not sure what you mean by this. But I mean right now, The rectangle is scaling up and down from sort of an "anchor point" In the top left corner. It may be hard to visualize but I am trying to get this "anchor point" In the center of the rectangle or object — malideux, May 06 '14 at 02:11

score 0 · Accepted Answer · answered May 06 '14 at 02:13

Changing the "origin point" so it becomes the center of the "zoom" is basically just the process of subtract half of d from the center point.

So, assuming the the center point is 28 ((25 / 2) + 15), you would simply then subtract d / 2 (25 / 2) from this point, 28 - (25 / 2) = 15 or near enough...

I modified the paintComponent method for testing, so the rectangle is always at the center of the panel, but you can supply arbitrary values in place of the originX and originY

@Override
public void paintComponent(Graphics g)//paints circle on the screen
{
    super.paintComponent(g); //prepares graphic object for drawing

    int originX = getWidth() / 2;
    int originY = getHeight() / 2;

    int x = originX - (d / 2);
    int y = originY - (d / 2);
    System.out.println(x + "x" + y);

    g.fillRect(x, y, d, d); //paints rectangle on screen
    //x , y, width, height

}

As for scaling an image, you should look at Graphics#drawImage(Image img, int x, int y, int width, int height, ImageObserver observer), beware though, this will scaling the image to the absolute size, it won't keep the image ratio.

A better solution might be to use a double value of between 0 and 1 and multiple the various elements by this value to get the absolute values you want

If It is not too much to ask, What is the easiest way to rotate the object along with scaling it when the slider is dragged? — malideux, May 06 '14 at 02:38
The eaist way, would be through the use of an `AffineTransform` — MadProgrammer, May 06 '14 at 02:41
For [example](http://stackoverflow.com/questions/20275424/rotating-image-with-affinetransform/20280225#20280225) and [example](http://stackoverflow.com/questions/23463174/getting-my-sprite-to-face-in-a-certain-direction-based-on-keyboard-input-java/23463387#23463387) — MadProgrammer, May 06 '14 at 02:41
Hey man, When I try to add an Image instead of a rectangle or circle object It does not scale or resize it only translates diagonally across the screen. Any ideas on how to make it scale? I asked it in my most recent question but You are a very big help and can probably help me lol! :) — malideux, May 06 '14 at 22:15

Java JPanel Scaling

1 Answers1