I suggest
- that you do not get your JPanel's Graphics or Graphics2D object via getGraphics as this object is not meant to be stable and will not work once the component has been repainted for any reason.
- that you instead do all your drawing in a single JPanel's paintComponent method, but first in that method call the super's method.
- that you again draw in only one JPanel, not two,
- that you draw your line in a BufferedImage, since that is a more permanent part of your image.
- That you get the BufferedImage's Graphics2D object via its createGraphics method
- That you properly dispose of the BufferedImage's Graphics object when done using it so as to conserve resources.
- that you display your BufferedImage in the paintComponent method of your JPanel (after calling the super method first)
- that you draw your box, the more fleeting portion of the image, directly in the paintComponent using int class variables to tell paintComponent where to draw and perhaps a class boolean variable to tell if to draw.
- and that most important, you review the tutorials on Swing graphics as to do this properly, you'll have to throw all old assumptions out and learn the correct way from the ground up (as we all had to do).
For example:
import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import javax.swing.*;
@SuppressWarnings("serial")
public class BufferedImageEg extends JPanel {
private static final int BI_WIDTH = 700;
private static final int BI_HEIGHT = 500;
private static final Color BACKGROUND = new Color(255, 255, 240);
private static final int THIS_PT_WIDTH = 12;
private static final int THIS_PT_HEIGHT = THIS_PT_WIDTH;
private static final float THIS_PT_STROKE_WIDTH = 2f;
private static final Color THIS_PT_BORDER_COLOR = Color.red;
private static final Color THIS_PT_FILL_COLOR = new Color(250, 250, 0, 125);
private static final int TIMER_DELAY = 30;
private static final int X_MIN = 0;
private static final int X_MAX = 100;
private static final double X_STEP = 0.1;
private static final double X_SCALE = (double) BI_WIDTH
/ ((double) X_MAX - X_MIN);
private static final double Y_SCALE = 8;
private static final float LINE_WIDTH = 4;
private static final Color LINE_COLOR = Color.blue;
private Point lastPoint = null;
private Point thisPoint = null;
private BufferedImage bImage = new BufferedImage(BI_WIDTH, BI_HEIGHT,
BufferedImage.TYPE_INT_RGB);
private double xValue = X_MIN;
public BufferedImageEg() {
Graphics biG = bImage.getGraphics();
biG.setColor(BACKGROUND);
biG.fillRect(0, 0, BI_WIDTH, BI_HEIGHT);
setBackground(BACKGROUND);
new Timer(TIMER_DELAY, new ActionListener() {
public void actionPerformed(ActionEvent e) {
timerActionPerformed(e);
}
}).start();
}
private void timerActionPerformed(ActionEvent e) {
if (xValue <= X_MAX) {
lastPoint = thisPoint;
double tempX = xValue;
double yValue = function(xValue);
tempX *= X_SCALE;
yValue *= Y_SCALE;
yValue = BI_HEIGHT / 2.0 - yValue;
thisPoint = new Point((int) tempX, (int) yValue);
if (lastPoint != null) {
drawInBufferedImage();
}
xValue += X_STEP;
} else {
((Timer) e.getSource()).stop();
thisPoint = null;
}
repaint();
}
private void drawInBufferedImage() {
Graphics2D g2 = bImage.createGraphics();
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
g2.setStroke(new BasicStroke(LINE_WIDTH, BasicStroke.CAP_ROUND,
BasicStroke.JOIN_ROUND));
g2.setColor(LINE_COLOR);
int x1 = lastPoint.x;
int y1 = lastPoint.y;
int x2 = thisPoint.x;
int y2 = thisPoint.y;
g2.drawLine(x1, y1, x2, y2);
g2.dispose();
}
@Override
public Dimension getPreferredSize() {
return new Dimension(BI_WIDTH, BI_HEIGHT);
}
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawImage(bImage, 0, 0, null);
Graphics2D g2 = (Graphics2D) g;
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
if (thisPoint != null) {
drawThisPoint(g2);
}
}
private void drawThisPoint(Graphics2D g2) {
int x = thisPoint.x - THIS_PT_WIDTH / 2;
int y = thisPoint.y - THIS_PT_HEIGHT / 2;
Graphics2D g2b = (Graphics2D) g2.create();
g2b.setStroke(new BasicStroke(THIS_PT_STROKE_WIDTH));
g2b.setColor(THIS_PT_FILL_COLOR);
g2b.fillOval(x, y, THIS_PT_WIDTH, THIS_PT_HEIGHT);
g2b.setColor(THIS_PT_BORDER_COLOR);
g2b.drawOval(x, y, THIS_PT_WIDTH, THIS_PT_HEIGHT);
g2b.dispose();
}
private double function(double x) {
return 24 * Math.sin(x / 12.0) * Math.sin(x);
}
private static void createAndShowGui() {
JFrame frame = new JFrame("BufferedImage Example");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(new BufferedImageEg());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}
