Developing a 2D game in Java ME - Part 3 - Revision history

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@@ Line 273: / Line 273: @@
 </code>
-Now create and configure all these classes on the canvas class. Create an <tt>init()</tt> method on the Canvas class.
+Now create and configure all these classes in the canvas class. Create an <tt>init()</tt> method in the Canvas class.
 <code java>
 public void init() {

@@ Line 155: / Line 155: @@
 As you may have noticed, the GameCanvas class is used. The GameCanvas is a special case of the Canvas class, optimized for games. It uses the following techniques:
 * Double buffering. The GameCanvas uses an off-screen image which is used for all painting operations. When painting is completed, it can be rendered to the screen using the <tt>flushGraphics()</tt> method. This eliminates flickering and gives a smoother animation.
-* Storing the key state in arrays. Through the <tt>getKeyStates()</tt> method you can access a bit array that indicates the state of each key using the constants defined in Canvas, like constant DOWN_PRESSED.
+* Storing the key state in arrays. Through the <tt>getKeyStates()</tt> method you can access a bit array that indicates the state of each key.
 Besides using GameCanvas, use a Thread to keep the animation running independently of MIDlet events. This way the animation will never wait for system events to repaint itself.

@@ Line 155: / Line 155: @@
 As you may have noticed, the GameCanvas class is used. The GameCanvas is a special case of the Canvas class, optimized for games. It uses the following techniques:
 * Double buffering. The GameCanvas uses an off-screen image which is used for all painting operations. When painting is completed, it can be rendered to the screen using the <tt>flushGraphics()</tt> method. This eliminates flickering and gives a smoother animation.
-* Storing the key state in arrays. Through the <tt>getKeyStates()</tt> method you can access a bit array that indicates the state of each key using the constants defined in Canvas: DOWN_PRESSED
+* Storing the key state in arrays. Through the <tt>getKeyStates()</tt> method you can access a bit array that indicates the state of each key using the constants defined in Canvas, like constant DOWN_PRESSED.
 Besides using GameCanvas, use a Thread to keep the animation running independently of MIDlet events. This way the animation will never wait for system events to repaint itself.

@@ Line 1: / Line 1: @@
-[[Category:Java ME]][[Category:Games]][[Category:How To]][[Category:Code Examples]][[Category:Symbian]][[Category:Series 40]]
+[[Category:Java ME]][[Category:Games]][[Category:How To]][[Category:Code Examples]][[Category:Symbian]][[Category:Series 40]][[Category:Series 40 Developer Platform 1.1]][[Category:Series 40 Developer Platform 2.0]][[Category:Nokia Belle]][[Category:Java Runtime 2.3 for Symbian]]
 {{Abstract|This article shows how to use Java ME's low-level interface classes to create the game screen and access key presses.
 This is the third in a series of articles that cover all the basics of developing an application for mobile devices using Java ME, learning the main libraries, classes, and methods available in Java ME.}}
 {{ArticleMetaData <!-- v1.1 -->
-|sourcecode=  [[Media:ArkanoidPart3Source.zip]]
+|sourcecode= [[Media:ArkanoidPart3Source.zip]]
-|installfile=  [[Media:ArkanoidPart3Binaries.zip]]
+|installfile= [[Media:ArkanoidPart3Binaries.zip]]
 |devices= Nokia 701, Nokia Asha 305
 |sdk= [http://www.developer.nokia.com/Develop/Java/Tools/ Nokia SDK 1.1 for Java], [http://www.developer.nokia.com/Develop/Java/Tools/ Nokia SDK 2.0 for Java]

@@ Line 3: / Line 3: @@
 This is the third in a series of articles that cover all the basics of developing an application for mobile devices using Java ME, learning the main libraries, classes, and methods available in Java ME.}}
 {{ArticleMetaData <!-- v1.1 -->
-|sourcecode= [http://sergioestevao.com/midp/files/2009/04/lesson3-source.rar Full Source Code]
+|sourcecode=  [[Media:ArkanoidPart3Source.zip]]
-|installfile= [http://sergioestevao.com/midp/files/2009/04/formacao3.jad Jad File], [http://sergioestevao.com/midp/files/2009/04/formacao3.jar Jar File]
+|installfile=  [[Media:ArkanoidPart3Binaries.zip]]
-|devices= <!-- Devices tested against - e.g. ''devices=Nokia 6131 NFC, Nokia C7-00'') -->
+|devices= Nokia 701, Nokia Asha 305
-|sdk= <!-- SDK(s) built and tested against (e.g. [http://linktosdkdownload/ Nokia Qt SDK 1.1]) -->
+|sdk= [http://www.developer.nokia.com/Develop/Java/Tools/ Nokia SDK 1.1 for Java], [http://www.developer.nokia.com/Develop/Java/Tools/ Nokia SDK 2.0 for Java]
-|platform= <!-- Compatible platforms - e.g. Symbian^1 and later, Qt 4.6 and later -->
+|platform= Series 40, Symbian
 |devicecompatability= <!-- Compatible devices e.g.: All* (must have internal GPS) -->
 |dependencies= <!-- Any other/external dependencies e.g.: Google Maps Api v1.0 -->
@@ Line 387: / Line 387: @@
 == Downloads ==
-* [http://sergioestevao.com/midp/files/2009/04/lesson3-source.rar Full Source Code]
+* [[Media:ArkanoidPart3Source.zip|Source files]]
-* [http://sergioestevao.com/midp/files/2009/04/formacao3.jad Jad File]
+* [[Media:ArkanoidPart3Binaries.zip|Binary files]]
-* [http://sergioestevao.com/midp/files/2009/04/formacao3.jar Jar File]
+Go to [[Developing a 2D game in Java ME - Part 4]]
-[[Developing a 2D game in Java ME - Part 4|Go To Part 4]]

@@ Line 71: / Line 71: @@
 import javax.microedition.lcdui.Graphics;
-public class MyCanvas extends Canvas{
+public class MyCanvas extends Canvas {
    int width;
@@ Line 85: / Line 85: @@
      height = getHeight();
      // set background color
-     g.setColor(0,0,0);
+     g.setColor(0, 0, 0);
      // clear screen
      g.fillRect(0, 0, width, height);
      // draw a red circle that represents a ball
-     g.setColor(255,0,0);
+     g.setColor(255, 0, 0);
      g.drawArc(100, 100, 5, 5, 0, 360);
      // draws a blue rectangle for the pad
-     g.setColor(0,0,255);
+     g.setColor(0, 0, 255);
      g.fillRect(100, 200, 15, 15);
+   }
@@ Line 120: / Line 120: @@
 public class MyCanvas extends GameCanvas implements Runnable{
 …
-public void start() {
+  public void start() {
-  run = true;
+    run = true;
-  Thread t = new Thread(this);
+    Thread t = new Thread(this);
-  t.start();
+    t.start();
-−
+  }
-public void stop() {
+  public void stop() {
-  run = false;
+    run = false;
-−
+  }
-public void run(){
+  public void run() {
-  init();
+    init();
-  while (run){
+    while (run) {
-    // update game elements, positions, collisions, etc..
+      // update game elements, positions, collisions, etc.
-    updateGameState();
+      updateGameState();
-    // check user input
+      // check user input
-    checkUserInput();
+      checkUserInput();
-    // render screen
+      // render screen
-    updateGameScreen();
+      updateGameScreen(getGraphics());
-    // redraws screen
+      // redraw screen
-    flushGraphics();
+      this.flushGraphics();
-    // controls at which rate the updates are done
+      // controls at which rate are the updates done
-    Thread.sleep(10);
+      try {
+   }
 …
+}
@@ Line 181: / Line 186: @@
 <code java>
 public class Ball extends Entity {
-   public int radium = 2;
+   public int radius = 2;
-   public Ball(int radium){
+   public Ball(int radius){
-     this.radium = radium;
+     this.radius = radius;
-     width = radium * 2;
+     width = radius * 2;
-     height = radium * 2;
+     height = radius * 2;
      // red color
      this.color = 0x00FF0000;
@@ Line 192: / Line 197: @@
    /**
-    * Paints the ball using a circle
+    * paints the ball
     */
    public void paint(Graphics g) {
      g.setColor(color);
-     g.fillArc(x, y, radium*2, radium*2, 0, 360);
+     g.fillArc(x, y, radius*2, radius*2, 0, 360);
+   }
-   /***
+   /**
-    * Updates the ball position.
+    * updates the ball position
     */
    public void update() {
      // update position
-     oldX=x;
+     oldX = x;
-     oldY=y;
+     oldY = y;
      x += speedX;
      y += speedY;

@@ Line 113: / Line 113: @@
 == Game loop ==
-Before you continue, you need to understand the way typical game applications works. A game or animation is built by repetitiously executing a piece of code. This piece of code tracks the value of the variables and updates the game state accordingly. Based on the game state, the code draws/paints/repaints the game screen with the elements that build the game. The values of the variables may change because of user interaction or internal game behavior.
+Before you continue, you need to understand the way typical game applications work. A game or animation is built by repetitiously executing a piece of code. This piece of code tracks the value of the variables and updates the game state accordingly. Based on the game state, the code draws/paints/repaints the game screen with the elements that build the game. The values of the variables may change because of user interaction or internal game behavior.
 This is created by putting the code that is repeated in a continuous loop. Before entering the loop, a variable can be checked to see if the game should still be running. If not, the loop can  be exited. The code in the loop should allow the current execution thread to sleep every few milliseconds to control the rate at which the game state is updated (that is, how fast the game screen should be refreshed).
@@ Line 150: / Line 150: @@
 As you may have noticed, the GameCanvas class is used. The GameCanvas is a special case of the Canvas class, optimized for games. It uses the following techniques:
 * Double buffering. The GameCanvas uses an off-screen image which is used for all painting operations. When painting is completed, it can be rendered to the screen using the <tt>flushGraphics()</tt> method. This eliminates flickering and gives a smoother animation.
-* Storing the key state in arrays. Trough the <tt>getKeyStates()</tt> method you can access a bit array that indicates the state of each key using the constants defined in Canvas: DOWN_PRESSED
+* Storing the key state in arrays. Through the <tt>getKeyStates()</tt> method you can access a bit array that indicates the state of each key using the constants defined in Canvas: DOWN_PRESSED
 Besides using GameCanvas, use a Thread to keep the animation running independently of MIDlet events. This way the animation will never wait for system events to repaint itself.
@@ Line 156: / Line 156: @@
 * The pad, our game avatar, is just a small rectangle that moves from left to right in the bottom of the screen.
-* The ball is first to the pad, and when you press fire it goes up vertically with the horizontal speed of the pad.
+* The ball, when hit with the pad it bounces to other direction
 * The bricks are static blocks in the upper part of the screen. When they are hit by the ball they disappear.
-The goal of the game is to make the bricks disappear as fast as possible, and not let the ball get away trough the bottom of the screen.
+The goal of the game is to make the bricks disappear as fast as possible, and not let the ball get away through the bottom of the screen.
 The game needs to keep track of three variables:
@@ Line 166: / Line 166: @@
 * Time remaining. The player must complete the game in a limited time.
-First define some classes to represent the game entities:
+First define some classes to represent the game entities.
-<center>
-<a href="http://sergioestevao.com/midp/files/2007/11/arkanoidscreenshot.png" title='Arkanoid Entities'><img src="http://sergioestevao.com/midp/files/2007/11/arkanoidscreenshot.png" alt='Arkanoid Entities' /></a>
-</center>
 The class Entity will be the parent for all the game entities. It provides the following functionalities:
@@ Line 177: / Line 174: @@
 * <strong>width, height</strong>: Defines the size of the entity.
 * <strong>update()</strong>: Defines the the behavior of the entity.
-* <strong>paint()</strong>: Method were the graphics class is used to draw the entity.
+* <strong>paint()</strong>: Method where the graphics class is used to draw the entity.
 * <strong>collided()</strong>: Helper function that allows to check collision between entities.

@@ Line 53: / Line 53: @@
 * '''keyPressed(), keyRepeated(), keyReleased()''' notify the canvas when the keypad is used.
 * '''pointerPressed(), pointerDragged(), pointerReleased()''' notify the canvas when the pointer is used, available on phones with a stylus.
-* '''paint()''' notifies the Canvas when it needs to paint the screen. This method gives access to the Graphics object.</li>
+* '''paint()''' notifies the Canvas when it needs to paint the screen. This method gives access to the Graphics object.
-* <tt>getWidth()</tt>, <tt>getHeight()</tt> give access to the current size of the screen available to be drawn on.
+* '''getWidth(), getHeight()''' give access to the current size of the screen available to be drawn on.
 The Graphics class provides the methods for direct drawing on the screen:
 * <strong>drawLine()</strong> draws a line.
-* <strong>drawRect()</strong>, fillRect draws a rectangle on the screen.
+* <strong>drawRect(), fillRect()</strong> draws a rectangle on the screen.
-* <strong>fillTriangle()</strong> draws a filled rectangle.
+* <strong>fillTriangle()</strong> draws a filled triangle.
-* <strong>drawArc()</strong> fillArc, draws an arc on the screen, can be used to draw circles.
+* <strong>drawArc(), fillArc()</strong> draws an arc on the screen, can be used to draw circles.
-* <strong>drawChar()</strong>, drawChars, drawString draws characters to the screen using the current font.
+* <strong>drawChar(), drawChars(), drawString()</strong> draws characters to the screen using the current font.
-* <strong>drawImage()</strong>, draws a bitmap image on the screen.
+* <strong>drawImage()</strong> draws a bitmap image on the screen.
-* <strong>setFont()</strong>, defines the current font.
+* <strong>setFont()</strong> defines the current font.
-* <strong>setColor()</strong>, defines the current color being used by the draw methods.
+* <strong>setColor()</strong> defines the current color being used by the draw methods.
 To create the game screen we need to extend the Canvas class and implement a custom paint method.