keeping shapes on a canvas with a paint tool

[javatrainee]

Hi,

I'm trying to write a basic paint tool, and cannot seem to keep the shapes drawn on the canvas. Each time a user clicks on the canvas, it draws a new shape, and deletes the previous shape.

Any idea how to keep all the shapes drawn on the canvas?

Help me please!!!

Code so far is as follows:

import java.awt.*;
import java.awt.event.*;

public class DTF extends Frame implements WindowListener
{
DrawToolCanvas myCanvas; // member variable

public DTF()
{
setTitle("Draw Tool Frame");
addWindowListener(this);
Button square, circle;
Panel myPanel = new Panel();
square = new Button("square"); square.setActionCommand("square");
circle = new Button("circle"); circle.setActionCommand("circle");
myPanel.add(square); myPanel.add(circle);
add("South", myPanel);
// DrawToolCanvas myCanvas = new DrawToolCanvas(); // local variable
myCanvas = new DrawToolCanvas(); // member variable
add("Center", myCanvas);
square.addActionListener(myCanvas);
circle.addActionListener(myCanvas);
setSize(400,400);
setLocation(200,200);
setVisible(true);
}

public void windowClosing(WindowEvent event) { System.exit(0); }
public void windowOpened(WindowEvent event) {}
public void windowIconified(WindowEvent event) {}
public void windowDeiconified(WindowEvent event) {}
public void windowClosed(WindowEvent event) {}
public void windowActivated(WindowEvent event) {}
public void windowDeactivated(WindowEvent event) {}

public static void main(String[] args)
{
new DTF();
}
}

class DrawToolCanvas extends Canvas implements MouseListener, ActionListener
{
int x, y;
boolean drawCircle;

public DrawToolCanvas()
{
x = -40;
y = -40;
drawCircle = true;
addMouseListener(this);
}

public void paint(Graphics g)
{
super.paint(g);
if(drawCircle)
{
g.setColor(Color.blue);
g.fillOval( x, y, 40, 40 );
}
else
{
g.setColor(Color.red);
g.drawRect(x, y, 40, 40);
}
}

public void actionPerformed(ActionEvent event)
{
if (event.getActionCommand().equals("square"))
drawCircle = false;
else if (event.getActionCommand().equals("circle"))
drawCircle = true;
}

public void mousePressed(MouseEvent e)
{
x = e.getX();
y = e.getY();
repaint();
}

public void mouseEntered(MouseEvent e) {}
public void mouseExited(MouseEvent e) {}
public void mouseReleased(MouseEvent e) {}
public void mouseClicked(MouseEvent e) {}
}

[nescafe]

oops!

[nescafe]

oops! number 2!

[nescafe]

public void paintComponent(Graphics g){
super.paintComponent(g);
.....}

First, comment out the line

super.paint(g)

Second, the update method of your canvas: update(g)
should be overridden to only call the paint method:

public void update(Graphics g){
     paint(g);
}

That'll fix your problem of having the shapes disappear w/ each successive click by the user.
I can't exactly explain the logic of how all this works but if you try out what I say it will indeed work.
Perhaps another forum user will be able to better explain how the painting works.

[fulcanelli]

Hi,

Thank you so much for your help. Works like a dream now!!

Have a great weekend.

[sjalle]

Sorry guys, but that doesn't fix the problem, if I minimize/restore this frame
then only the last shape is visible. I call this method "drawing in the sand".

But, we just fixed that in another thread:

http://forums.devx.com/showthread.ph...144#post440144

Here I have "fixed" your code using double buffering, and the method could
well be called "tattoing" . Its not a good one, the link above shows the
preferred way of solving this.

import java.awt.*;
import java.awt.event.*;
import java.awt.image.*;

public class DTF
    extends Frame
    implements WindowListener {
  DrawToolCanvas myCanvas; // member variable

  public DTF() {
    setTitle("Draw Tool Frame");
    addWindowListener(this);
    Button square, circle;
    Panel myPanel = new Panel();
    square = new Button("square");
    square.setActionCommand("square");
    circle = new Button("circle");
    circle.setActionCommand("circle");
    myPanel.add(square);
    myPanel.add(circle);
    add("South", myPanel);
    myCanvas = new DrawToolCanvas(); // member variable
    add("Center", myCanvas);
    square.addActionListener(myCanvas);
    circle.addActionListener(myCanvas);
    setSize(400, 400);
    setLocation(200, 200);
    setVisible(true);
    myCanvas.prepBuffer();
  }

  public void windowClosing(WindowEvent event) {
    System.exit(0);
  }

  public void windowOpened(WindowEvent event) {}

  public void windowIconified(WindowEvent event) {}

  public void windowDeiconified(WindowEvent event) {}

  public void windowClosed(WindowEvent event) {}

  public void windowActivated(WindowEvent event) {}

  public void windowDeactivated(WindowEvent event) {}

  public static void main(String[] args) {
    new DTF();
  }
}

class DrawToolCanvas
    extends Canvas
    implements MouseListener, ActionListener {
  int x, y;
  boolean drawCircle;
  BufferedImage memImg=null;
  Graphics memG=null;

  public DrawToolCanvas() {
    x = -40;
    y = -40;
    drawCircle = true;
    addMouseListener(this);
    prepBuffer();
  }

  public void prepBuffer() {
    memImg=new BufferedImage(1024,1024,BufferedImage.TYPE_INT_RGB);
    memG=memImg.getGraphics();
    memG.setColor(Color.white);
    memG.fillRect(0,0,getWidth(), getHeight());
  }
  public void update(Graphics g) {
    paint(g);
  }
  public void paint(Graphics g) {
    if (drawCircle) {
      memG.setColor(Color.blue);
      memG.fillOval(x, y, 40, 40);
    }
    else {
      memG.setColor(Color.red);
      memG.drawRect(x, y, 40, 40);
    }
    g.drawImage(memImg,0,0,this);
  }

  public void actionPerformed(ActionEvent event) {
    if (event.getActionCommand().equals("square"))
      drawCircle = false;
    else if (event.getActionCommand().equals("circle"))
      drawCircle = true;
  }

  public void mousePressed(MouseEvent e) {
    x = e.getX();
    y = e.getY();
    repaint();
  }

  public void mouseEntered(MouseEvent e) {}

  public void mouseExited(MouseEvent e) {}

  public void mouseReleased(MouseEvent e) {}

  public void mouseClicked(MouseEvent e) {}
}