Best way to determine optimal font size given some text in a rectangle

Question

Hi Folks,
I have a preview panel in which I am showing some text for the current selected date using a date format.
I want to increase the size of the applied font so that it scales nicely when the panel in which it is drawn is resized.
I want to know the best way in terms of performance to achieve the target. I did some reading about AffineTransform and determining by checking ina loop which is the correct size, but it does not feel like a good way.
I would appreciate some tips.
Cheers.
Ravi

Answer 1

import java.awt.*;
import java.awt.font.*;
import java.awt.geom.*;
import javax.swing.*;
public class ScaledText extends JPanel {
    String text = "Sample String";
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        Font font = g2.getFont().deriveFont(16f);
        g2.setFont(font);
        FontRenderContext frc = g2.getFontRenderContext();
        int w = getWidth();
        int h = getHeight();
        float[][] data = {
            { h/8f, w/3f, h/12f }, { h/3f, w/4f, h/8f }, { h*3/4f, w/2f, h/16f }
        for(int j = 0; j < data.length; j++) {
            float y = data[j][0];
            float width = data[j][1];
            float height = data[j][2];
            float x = (w - width)/2f;
            Rectangle2D.Float r = new Rectangle2D.Float(x, y, width, height);
            g2.setPaint(Color.red);
            g2.draw(r);
            float sw = (float)font.getStringBounds(text, frc).getWidth();
            LineMetrics lm = font.getLineMetrics(text, frc);
            float sh = lm.getAscent() + lm.getDescent();
            float xScale = r.width/sw;
            float yScale = r.height/sh;
            float scale = Math.min(xScale, yScale);
            float sx = r.x + (r.width - scale*sw)/2;
            float sy = r.y + (r.height + scale*sh)/2 - scale*lm.getDescent();
            AffineTransform at = AffineTransform.getTranslateInstance(sx, sy);
            at.scale(scale, scale);
            g2.setFont(font.deriveFont(at));
            g2.setPaint(Color.blue);
            g2.drawString(text, 0, 0);
    public static void main(String[] args) {
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(new ScaledText());
        f.setSize(400,400);
        f.setLocationRelativeTo(null);
        f.setVisible(true);
}