Moving actors

Example 1: The fish should swim back and forth

This can only be achieved with a selection using if. In this example the method isNearBorder() checks if the fish is in a cell next to the grid's border. If this is the case, it swims back.

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import ch.aplu.jgamegrid.*;
import java.awt.Color;

public class JGameEx1 extends GameGrid
{
  public JGameEx1()
  {
    super(10, 10, 60, Color.red, "sprites/reef.gif");
    Fish nemo = new Fish();
    addActor(nemo, new Location(2, 4));
    show();
  }

  public static void main(String[] args)
  {
    new JGameEx1();
  }
}

// ------------- class Fish --------------------
class Fish extends Actor
{
  public Fish()
  {
    super("sprites/nemo.gif");
  }

  public void act()
  {
    move();
    if (isNearBorder())
      turn(180);
  }
}

Explaining the program code:

move()	This moves the actor to the next cell. When initializing an actor, its starting direction of 0° is set (east). The direction can be changed with the method setDirection() (absolute) or turn() (relativ)
if (isNearBorder()) turn(180)	Checks if nemo is in a border cell and turns it 180°

Example 2: Mirroring actors

With setHorzMirror(boolean b) a sprite of an actor can be mirrored. If b is true, the mirrored picture is shown. If b is false the mirrored picture is set back to its normal view.

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// JGameEx2.java

import ch.aplu.jgamegrid.*;
import java.awt.Color;

public class JGameEx2 extends GameGrid
{
  public JGameEx2()
  {
    super(10, 10, 60, Color.red, "sprites/reef.gif");
    Fish2 nemo = new Fish2();
    addActor(nemo, new Location(2, 4));
    show();
  }

  public static void main(String[] args)
  {
    new JGameEx2();
  }
}

// ------------- class Fish --------------------
class Fish2 extends Actor
{
  public Fish2()
  {
    super("sprites/nemo.gif");
  }

  public void act()
  {
    move();
    if (isNearBorder())
    {
      turn(180);
      setHorzMirror(!isHorzMirror());
    }
  }
}

Explaining the program code:

setHorzMirror(true)	Mirrors the sprite. By default setHorzMirror(b) is set to false
isHorzMirror()	Returns true if the sprite is mirrored
setHorzMirror(!isHorzMirror())	If the sprite is not mirrored, mirror it and vice veras

Example 3: Controlling actors movements with random numbers

The fish changes its direction randomly after each step by 5° or -5°.

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// JGameEx3.java

import ch.aplu.jgamegrid.*;
import java.awt.Color;

public class JGameEx3 extends GameGrid
{
  public JGameEx3()
  {
    super(50, 50, 12, "sprites/reef.gif");
    Fish nemo = new Fish();
    addActor(nemo, new Location(10, 20));
    show();
  }

  public static void main(String[] args)
  {
    new JGameEx3();
  }
}

// ------------- class Fish --------------------
class Fish extends Actor
{
  public Fish()
  {
    super("sprites/nemo.gif");
  }

  public void act()
  {
    if (Math.random() < 0.5 )
      turn(5);
    else
      turn(-5);

    if (isNearBorder())
    {
      turn(180);
      setHorzMirror(!isHorzMirror());
    }
    move();
  }
}

Explaining the program code:

Math.random()	Returns a multi-digit random number between 0 and 1
if (Math.random() < 0.5) turn(5); else turn(-5);	More or less 50% of the random numbers are smaller than 0.5. This turns the fish 5°. Otherwise it is turned -5°

Exercises: Exercise 1

GameGrid: Game programming with Java	Deutsch
Research project PHBern

GameGrid: Game programming with Java

Moving actors