Fitting text into BufferedImage

Question

I wrote this program to find a way I could draw a String centered onto a BufferedImage of any size (in this case, the size of the BufferedImage is the same as the JPanel its in) and location. When I resize the JFrame, the text flickers as it repositions itself in the BufferedImage and I don't know why.

import java.awt.*;
import java.awt.image.BufferedImage;

import javax.swing.*;

@SuppressWarnings("serial")
class test extends JPanel
{
    double scale = 0;
    String draw = "1";

test()
{
    setPreferredSize(new Dimension(600, 600));
}

public void paintComponent(Graphics g)
{
    super.paintComponent(g);
    Graphics2D g2 = (Graphics2D)g;
    paintText(g2, 0, 0);
}

public void paintText(Graphics2D g, int x, int y)
{   
    g.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
    BufferedImage bi = new BufferedImage(getWidth(), getHeight(), BufferedImage.TYPE_INT_RGB);
    Graphics2D big = (Graphics2D) bi.getGraphics();
    FontMetrics fm = big.getFontMetrics(); 

    scale = bi.getHeight()/(fm.getHeight());
    double xt = -(((scale*bi.getWidth())-bi.getWidth())/2);
    double yt = -(((scale*bi.getHeight())-bi.getHeight())/2);
    big.translate(xt, yt); 
    big.scale(scale, scale);
    big.drawString(draw, (bi.getWidth()/2)-(fm.stringWidth(draw)/2), (bi.getHeight()/2)+(fm.getHeight()/4)+1);
    g.drawImage(bi, x, y, this);
}

public static void main(String[] args)
{
    JFrame frame = new JFrame("test");
    frame.add(new test());
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.pack();
    frame.setVisible(true);
}
}

Answer 1

The major problem is your attempt to translate and the center the text within the BufferedImage, the calculations are causing a certain amount of drift as the size of the window is changed, meaning that they don't produce an accurate position.

After much stuffing around, I basically threw out your BufferedImage and setScale approach and simple derived a new font based on the scale property.

Now, you could still generate a BufferedImage, but I would use the resulting FontMetrics to determine the actual size of the image and simply render the image at the center position of the frame...but that's me

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.geom.AffineTransform;
import java.awt.image.BufferedImage;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

class Test101 extends JPanel {

    double scale = 0;
    String draw = "1";

    Test101() {
        setPreferredSize(new Dimension(600, 600));
    }

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D) g;
        paintText(g2, 0, 0);

        int x = getWidth() / 2;
        int y = getHeight() / 2;
        g2.setColor(Color.RED);
        g2.drawLine(x, 0, x, getHeight());
        g2.drawLine(0, y, getWidth(), y);
    }

    public void paintText(Graphics2D g, int x, int y) {
        
        Graphics2D g2d = (Graphics2D) g.create();
        g2d.setColor(Color.BLACK);
        g2d.fillRect(0, 0, getWidth(), getHeight());
        
        FontMetrics fm = g.getFontMetrics();
        System.out.println(fm.getAscent());
        scale = getHeight() / (fm.getHeight());
        
        Font font = g.getFont().deriveFont(Font.PLAIN, AffineTransform.getScaleInstance(scale, scale));
        g2d.setFont(font);
        g2d.setColor(Color.WHITE);
        fm = g.getFontMetrics(font);
        int xPos = (getWidth() - fm.stringWidth(draw)) / 2;
        int yPos = ((getHeight() - fm.getHeight()) / 2) + fm.getAscent();
        g2d.drawString(draw, xPos, yPos);
        g2d.dispose();
        
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame("test");
                frame.add(new Test101());
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }
}