scaling a font when resizing by dragging

[Rob Byrd]

I am using g.drawString() in paintComponent() to display a text string on a JPanel. I am resizing the JPanel by dragging it on a canvas (another JPanel). I want the text string to resize as well. Is there a way to do this so that the displayed string stays within the bounds of the JPanel. The text string has to increase when the dragged JPanel increases and decrease when the dragged JPanel decreases in size. In other words, the bounds of the text string has to change more or less in proportion to the bounds of the dragged JPanel.

Thanks for your help.

[Brian Cole]

Originally posted by jack swallow:
I am using g.drawString() in paintComponent() to display a text string on a JPanel. I am resizing the JPanel by dragging it on a canvas (another JPanel). I want the text string to resize as well.

There are several ways to do this. Three come to mind:

1. call g.setFont() to set a larger or smaller font (could use g.getFontMetrics().charsWidth() to test font size)

2. call ((Graphics2D)g).scale()

3. replace the JPanel with a JSVGCanvas

The first two may require code to detect resizing. The last one depends on an external library.
[ July 13, 2007: Message edited by: Brian Cole ]

[Craig Wood]

import java.awt.*;
import java.awt.font.*;
import java.awt.geom.AffineTransform;
import javax.swing.*;
 
public class FittingAFont extends JPanel {
    String s = "Hello World";
 
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_TEXT_ANTIALIASING,
                            RenderingHints.VALUE_TEXT_ANTIALIAS_ON);
        g2.setRenderingHint(RenderingHints.KEY_FRACTIONALMETRICS,
                            RenderingHints.VALUE_FRACTIONALMETRICS_ON);
        Font font = g2.getFont().deriveFont(36f);
        g2.setFont(font);
        FontRenderContext frc = g2.getFontRenderContext();
        LineMetrics metrics = font.getLineMetrics(s, frc);
        // Try omitting the descent from the height variable.
        float height = metrics.getAscent() + metrics.getDescent();
        double width = font.getStringBounds(s, frc).getWidth();
        int w = getWidth();
        int h = getHeight();
        double xScale = w/width;
        double yScale = (double)h/height;
        double x = (w - xScale*width)/2;
        double y = (h + yScale*height)/2 - yScale*metrics.getDescent();
        AffineTransform at = AffineTransform.getTranslateInstance(x, y);
        at.scale(xScale, yScale);
        g2.setFont(font.deriveFont(at));
        g2.drawString(s, 0, 0);
    }
 
    public static void main(String[] args) {
        JFrame f = new JFrame("drag edges");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(new FittingAFont());
        f.setSize(175,90);
        f.setLocation(200,200);
        f.setVisible(true);
    }
}

[Brian Cole]

Mr. Wood's implementation uses approach #1.

It could be modified to use approach #2 like this:

    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D)g.create();
        g2.setRenderingHint(RenderingHints.KEY_TEXT_ANTIALIASING,
                            RenderingHints.VALUE_TEXT_ANTIALIAS_ON);
        g2.setRenderingHint(RenderingHints.KEY_FRACTIONALMETRICS,
                            RenderingHints.VALUE_FRACTIONALMETRICS_ON);
        Font font = g2.getFont(); [I]//.deriveFont(36f);[/I]
        g2.setFont(font);
        FontRenderContext frc = g2.getFontRenderContext();
        LineMetrics metrics = font.getLineMetrics(s, frc);
        // Try omitting the descent from the height variable.
        float height = metrics.getAscent() + metrics.getDescent();
        double width = font.getStringBounds(s, frc).getWidth();
        int w = getWidth();
        int h = getHeight();
        [I]/*
        double xScale = w/width;
        double yScale = (double)h/height;
        double x = (w - xScale*width)/2;
        double y = (h + yScale*height)/2 - yScale*metrics.getDescent();
        AffineTransform at = AffineTransform.getTranslateInstance(x, y);
        at.scale(xScale, yScale);
        g2.setFont(font.deriveFont(at));
        g2.drawString(s, 0, 0);
        */[/I]
        [B]g2.scale(w/width, h/height);
        g2.drawString(s, 0, metrics.getAscent()-1);[/B]
    }

[edit: I'm not sure you really need the setRenderingHint() stuff.]
[ July 13, 2007: Message edited by: Brian Cole ]