On java.net, there was a post by kfarnham about my articles on writing Pac-man game in JavaFX. He wondered whether there would be a fifth article. The answer is positive. Yesterday, my last article of a series, “Writing the Pac-Man Game in JavaFX Part 5“, had been published on insiderRIA.com. This final article detailed the chasing algorithms of the ghosts. I think it is probably one of the most interesting things in the code.

When writing the game, there are a few points we need to consider before designing an algorithm of the ghosts, such as effectiveness, randomness, simplicity. You can refer to the article about considerations on these aspects. An excerpt from the article is listed below in blue text. It discussed the choice of a proper algorithm. This algorithm not only serves as the chasing logic, it can also control the escaping behavior of the ghosts.

. . . . . .
After some thinking, I found that the distance between a ghost and the Pac-Man is a good ranking metric. The shorter the distance is, the higher the score is given to a particular choice. The advantages of using the distance as a metric are obvious. It is very simple and can be caculated easily. Besides, this algorithm makes a ghost move in the direction that has the shortest distance to thePac-Man. To illustrate this algorithm, let’s look at the below figure.

In the figure, the ghost Blinky is moving into an intersection from the right to the left. When it reaches the intersection, it has three possible choices of its next movement: to go up, to go down and to continue heading left. Going down is not a valid move because it hits the border of the maze. So we need to compare the other two options. The below table shows the computation of the distance of the two possible moves:

As shown in the table, the distance from the intersection to the Pac-Man character is 13 (The distance between two adjacent dots is 1). If Blinky goes up, the distance is reduced to 12. If it heads left, the distance becomes 14. Therefore, going up seems a better choice for Blinky. In this way, Blinky should be able to get closer and closer to the Pac-Man and eventually catches him.

Of course, this simple algorithm does not take into consideration for the walls in the maze. For this reason, sometimes the calculated score does not in fact represent the shortest path. However, this inaccuracy makes the ghosts appear “stupid” in the game, which is the randomness we want to achieve in the behavior. So we are going to implement it in our code. We rewrite the class MoveDecision. When the function evaluate() calculates a score, it takes in two arguments: the reference to Pac-Man instance and whether the ghost is in a hollow state. The variable distance is used to compute the score. If the ghost is going after the Pac-Man character, the score is 500-distance, which means a shorter distance yields a higher score. If the Pac-Man is hunting the ghosts(when they are hollow), the score is caculated as 500+distance. This makes the ghosts running away from the Pac-Man.
. . . . . .

Now that all the articles had been published and I hope you enjoyed reading them. The game was originally written in JavaFX 1.0, and was compatible with JavaFX 1.1. Because multi-inheritance has been removed in JavaFX 1.2, I made some minor changes to the code. The abstract class MovingObject had been changed to mixin class. The code for JavaFX 1.2 can be download from JavaFX Game Download Page.

You can now click on the below image to play the completed Pac-Man game, it is based on the newly released JavaFX 1.2 . With the improved performance, the game run very smoothly.

Related Articles:

JavaFX Pac Man Part 5
Develop Games in JavaFX
JavaFX MineSweeper Demo Game
JavaFX Demo Game: LinkUP
WidgetFX Game Widgets: Pac-Man
My First JavaFX Game Demo
JavaFX Discussion Blogs

The Featured Articles on insideRIA.com:

May 14, 2009: Writing the Pac-Man Game in JavaFX - Part 1

May 21, 2009: Writing the Pac-Man Game in JavaFX - Part 2

May 28, 2009: Writing the Pac-Man Game in JavaFX - Part 3

June 4, 2009: Writing the Pac-Man Game in JavaFX - Part 4

June 11, 2009:Writing the Pac-Man Game in JavaFX - Part 5

My latest article of a series, “Writing the Pac-Man Game in JavaFX Part 4“, was out on June 4. As we continue on bulding the game, the articles are getting more and more interesting now.

In this fourth article, the interaction between Pac-Man character and the four ghosts was implemented. The article showed how to determine whether the Pac-man character and a ghost touched each other. A simplified equation was applied to achieve better performance. When Pac-man touches a ghost, he can eat it if the ghost is hollow. The ghost then is thrown back to the cage again. Otherwise, the ghost eats the Pac-man, at this moment, an animation of showing a dying Pac-Man appears. This is in fact a shrinking circle which disappears at the end of the animation. The animation is accomplished by the DyingPacMan class.

The below figure depicts the animation process of the dying Pac-man character.

The code of DyingPacMan.fx is listed below:

public class DyingPacMan extends Arc {

  var timeline = Timeline {
     repeatCount: 1
     keyFrames: [
        KeyFrame {
           time: 600ms
           action: function() {
           // hide the pacMan character & ghosts before the animation
              maze.pacMan.visible = false;

              for ( g in maze.ghosts ) {
                 g.hide();
              }
              visible = true;
            }
           values: [ startAngle => 90, length=>360 ];
         },
        KeyFrame {
           time: 1800ms
           action: function() {
              visible = false;
            }
           values: [ startAngle => 270 tween Interpolator.LINEAR,
                     length => 0 tween Interpolator.LINEAR ]
         },
      ]
    }

 ... code omitted ...
}

As you can see it in the code, there are two keyframes of the animation. Interpolations of two instance variables, startAngle and length, are involved during the animation. To better illustrate this process, the below figure shows the change of the shape against a timeline. The animation started with a pause of 600ms and then the first key frame appears, which is a full circle. After that, the full circle will gradually turns into nothing(empty circle). This effect is done by the interpolation provided by JavaFX API.

Hope you enjoy reading the articles. You can use arrow keys to play the current version of the game. The ghosts are moving randomly which makes the game less challenging. In the next article, I will introduced a better algorithm. Try it by clicking the below screenshot:

Related Articles:

More articles on JavaFX Games: Developing Games in JavaFX
Source of the Pac-Man Game
JavaFX Demo Game: MineSweeper
JavaFX Demo Game: LinkUP
Game Widgets for WidgetFX: Pac-Man
My JavaFX Demo Game: Pac-Man

The 2nd article of the series, “Writing the Pac-Man Game in JavaFX“, is published today.

The first article introduced a data model in Java and the JavaFX drawing logic of the maze. In the 2nd article, the animation part of the Pac-Man character is detailed. When you are reading, you can click on the java web start links to see the Pac-Man opening and closing mouths, and gradually moving inside the maze. The keyboard handling code is illustrated as well.

Some JavaFX features demostrated in these two articles include:

. shapes
. keyboard handling
. animation timeline
. java code integration
. Transfromation

Hope you can enjoy reading the articles. You can use arrow keys to play a no-ghost version of the game. The Pac-Man character now can move around and gobble dots. Try it by clicking the below screenshot:

Related Articles:

Develop Games in JavaFX

My JavaFX Demo Game: Pac-Man

After the release of JavaFX 1.0, I wrote a Pac-Man game using the JavaFX API. Many people were quite interested in the game. They either enjoyed playing it or asked me for the details fo the JavaFX code. JavaFX expert Jim Weaver invited me to write some articles about the process of building the game. After a few weeks’ hard work, with Jim’s constructive ideas and great help in proofreading, I finished the articles. Now they are published on insideRIA.com, an O’Reilly’s web site, as featured articles. There will be 5 articles in total and they will run through the coming 5 weeks.

In each article, there are a few web start links that you can click on and start a JavaFX program to see how it works. If you follow the 5 articles, you will find out how the game is built bit by bit. I hope the articles can help people who want to learn JavaFX or want to develop games in JavaFX. Thanks Jim for making these articles possible. My thanks also goes to Rich, the editor of insideRIA.com.

Here is the links for the articles:

May 14, 2009:
Writing the Pac-Man Game in JavaFX - Part 1
May 21, 2009:
Writing the Pac-Man Game in JavaFX - Part 2
May 28, 2009:
Writing the Pac-Man Game in JavaFX - Part 3
June 4, 2009:
Writing the Pac-Man Game in JavaFX - Part 4
June 11, 2009:
Writing the Pac-Man Game in JavaFX - Part 5

Related articles:
Answer: Blinky, Pinky, Inky and Clyde from Jim Weaver’s Blog

My JavaFX Demo Game: PACMAN

JavaFX Demo Game: PAC-MAN

UPDATE: June 30, 2009
If you are interested in how to write the Pac-Man game in JavaFX, the source code of this game, please check out this article:

How to Write the Pac-Man Game with JavaFX
or Articles on Writing the JavaFX Pac-Man Game

I spent some time to implement the classic game “PAC MAN”. It demos many features of the JavaFX language. Right now, it is a “simplified” PACMAN Game. I am working on the code and hopefully to complete the PACMAN game soon. Source code is not released yet because I plan to do so when I finish the whole game. A blog of writing this game will be available soon. Stay tuned.

Usage:
Arrow keys to move and control to pac-man to eat all dots inside the maze. The big dots are magic dots which allow the pac-man to eat ghosts.

JavaFX Features Demostrated:

• Bindings
• Animations
• Effects
• Transforms
• Multiple inheritant
• Java classes integration
• Declarative statements
• Sequences, how to map 2D arrays into a 1D Sequence
• Handling keyboard events

JRE 1.5+ required, JRE1.6 U10 is better, it will take some time for first time launching the game …

My JavaFX code is compatible with the newly released JavaFX 1.0. JavaFX is for Windows and Mac for now. The unofficial JavaFX SDK of Linux can be found here:
http://silveiraneto.net/2008/12/06/javafx-sdk-10-on-linux/

If you cannot play now, you can watch the video:

Unrelated links:

JavaFX Articles

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