Source Code : Use pointer events to draw onto the Canvas

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Use pointer events to draw onto the Canvas

/*--------------------------------------------------
* Doodle.java
*
* Use pointer events to draw onto the Canvas
*
* Example from the book:     Core J2ME Technology
* Copyright John W. Muchow   http://www.CoreJ2ME.com
* You may use/modify for any non-commercial purpose
*-------------------------------------------------*/  
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;

public class Doodle extends MIDlet
{
  private Display  display;       // The display
  private DoodleCanvas canvas;   // Canvas 
 
  public Doodle()
  {
    display = Display.getDisplay(this);
    canvas  = new DoodleCanvas(this);
  }
 
  protected void startApp()
  {
    display.setCurrent( canvas );
  }
 
  protected void pauseApp()
  { }

  protected void destroyApp( boolean unconditional )
  { }
 
  public void exitMIDlet()
  {
    destroyApp(true);
    notifyDestroyed();
  }
}

/*--------------------------------------------------
* Class DoodleCanvas
*
* Pointer event handling
*-------------------------------------------------*/
class DoodleCanvas extends Canvas implements CommandListener
{
  private Command cmExit;          // Exit midlet
  
  private Command cmClear;         // Clear display
  
  private int startx = 0,   // Where pointer was clicked
              
              starty = 0,
              
              currentx = 0, // Current location
              
              currenty = 0;
  private Doodle midlet;
  private boolean clearDisplay = false;

  /*--------------------------------------------------
  * Constructor
  *-------------------------------------------------*/
  public DoodleCanvas(Doodle midlet)
  {
    this.midlet = midlet;
    
    // Create exit command & listen for events
    cmExit = new Command("Exit", Command.EXIT, 1);
    cmClear = new Command("Clear", Command.SCREEN, 1);    
    addCommand(cmExit);
    addCommand(cmClear);
    setCommandListener(this);
  } 

  /*--------------------------------------------------
  * Paint the text representing the key code 
  *-------------------------------------------------*/
  protected void paint(Graphics g)
  {
    // Clear the background (to white)
    if (clearDisplay)
    {
      g.setColor(255, 255, 255);
      g.fillRect(0, 0, getWidth(), getHeight());
      
      clearDisplay = false;
      startx = currentx = starty = currenty = 0;
      
      return;
    }
    
    // Draw with black pen
    g.setColor(0, 0, 0);
    
    // Draw line
    g.drawLine(startx, starty, currentx, currenty);
    
    // New starting point is the current position
    startx = currentx;
    starty = currenty;
  }

  /*--------------------------------------------------
  * Command event handling
  *-------------------------------------------------*/  
  public void commandAction(Command c, Displayable d)
  {
    if (c == cmExit)
      midlet.exitMIDlet();
    else if (c == cmClear)
    {
      clearDisplay = true; 
      repaint();
    }
  }

  /*--------------------------------------------------
  * Pointer pressed
  *-------------------------------------------------*/  
  protected void pointerPressed(int x, int y)
  {
    startx = x;
    starty = y;
  }

  /*--------------------------------------------------
  * Pointer moved
  *-------------------------------------------------*/  
  protected void pointerDragged(int x, int y)
  {
    currentx = x;
    currenty = y;       
    repaint();
  } 
}


           
       

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