An implementation of HighlightPainter that underlines text with a thick line
/*
Java Swing, 2nd Edition
By Marc Loy, Robert Eckstein, Dave Wood, James Elliott, Brian Cole
ISBN: 0-596-00408-7
Publisher: O'Reilly
*/
// LineHighlightPainter.java
//An implementation of HighlightPainter that underlines text with a thick line.
//
import java.awt.BorderLayout;
import java.awt.Graphics;
import java.awt.Rectangle;
import java.awt.Shape;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.text.BadLocationException;
import javax.swing.text.Caret;
import javax.swing.text.DefaultCaret;
import javax.swing.text.Highlighter;
import javax.swing.text.JTextComponent;
public class LineHighlightPainter implements Highlighter.HighlightPainter {
// paint a thick line under one line of text, from r extending rightward to
// x2
private void paintLine(Graphics g, Rectangle r, int x2) {
int ytop = r.y + r.height - 3;
g.fillRect(r.x, ytop, x2 - r.x, 3);
}
// paint thick lines under a block of text
public void paint(Graphics g, int p0, int p1, Shape bounds, JTextComponent c) {
Rectangle r0 = null, r1 = null, rbounds = bounds.getBounds();
int xmax = rbounds.x + rbounds.width; // x coordinate of right edge
try { // convert positions to pixel coordinates
r0 = c.modelToView(p0);
r1 = c.modelToView(p1);
} catch (BadLocationException ex) {
return;
}
if ((r0 == null) || (r1 == null))
return;
g.setColor(c.getSelectionColor());
// special case if p0 and p1 are on the same line
if (r0.y == r1.y) {
paintLine(g, r0, r1.x);
return;
}
// first line, from p1 to end-of-line
paintLine(g, r0, xmax);
// all the full lines in between, if any (assumes that all lines have
// the same height--not a good assumption with JEditorPane/JTextPane)
r0.y += r0.height; // move r0 to next line
r0.x = rbounds.x; // move r0 to left edge
while (r0.y < r1.y) {
paintLine(g, r0, xmax);
r0.y += r0.height; // move r0 to next line
}
// last line, from beginning-of-line to p1
paintLine(g, r0, r1.x);
}
public static void main(String args[]) {
// extend DefaultCaret as an anonymous inner class
Caret lineHighlightPainterCaret = new DefaultCaret() {
private Highlighter.HighlightPainter lhp = new LineHighlightPainter();
// override getSelectionPainter to return the LineHighlightPainter
protected Highlighter.HighlightPainter getSelectionPainter() {
return lhp;
}
};
JFrame frame = new JFrame("LineHighlightPainter demo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JTextArea area = new JTextArea(9, 45);
area.setCaret(lineHighlightPainterCaret);
area.setLineWrap(true);
area.setWrapStyleWord(true);
area
.setText("This is the story\nof the hare who\nlost his spectacles.");
frame.getContentPane().add(new JScrollPane(area), BorderLayout.CENTER);
frame.pack();
frame.setVisible(true);
}
}
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