(#20) added behaviors example

src/example/java/tech/fastj/example/behaviors/Main.java

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+package tech.fastj.example.behaviors;
+
+import tech.fastj.engine.FastJEngine;
+import tech.fastj.graphics.display.Display;
+import tech.fastj.graphics.game.Polygon2D;
+import tech.fastj.graphics.game.RenderStyle;
+import tech.fastj.graphics.util.DrawUtil;
+
+import tech.fastj.systems.behaviors.Behavior;
+import tech.fastj.systems.control.SimpleManager;
+
+import java.awt.Color;
+
+public class Main extends SimpleManager {
+
+    @Override
+    public void init(Display display) {
+
+        /* Behaviors in FastJ */
+
+        /* FastJ's behavior system provides a simple and effective way to control GameObjects.
+         *
+         * A behavior:
+         * - Is any class that implements the Behavior interface
+         * - can be attached to any GameObject
+         * - has instances, allowing behaviors to be used more than one GameObject at a time
+         * - provides methods to control game objects through SimpleManager/Scene initialization
+         *   and updating */
+
+
+        /* Let's jump straight into it. Since a Behavior is just a class, we can simply create one.
+         * From here, jump over to tech.fastj.example.behaviors.SimpleMovementBehavior.java to see
+         * what makes up the behavior. */
+        SimpleMovementBehavior movementBehavior = new SimpleMovementBehavior();
+
+
+        /* To use the Behavior, we need to attach it to a game object.
+         * For this demonstration, we'll create a simple box.
+         * Its starting position will be (0, 0), and its rotation will be 0 degrees -- keep a close
+         * eye on how the behavior affects these properties. */
+        Polygon2D box = Polygon2D.fromPoints(DrawUtil.createBox(0f, 0f, 50f));
+
+        /* And lastly, we need to attach the behavior to the game object. It's as simple as calling
+         * gameObject.addBehavior(Behavior, SimpleManager/Scene) -- the SimpleManager/Scene is the
+         * manager the behavior is in. */
+        box.addBehavior(movementBehavior, this);
+        drawableManager.addGameObject(box);
+
+
+        /* Pre-defined Behaviors */
+
+        /* FastJ also contains some pre-defined behaviors to avoid having users create an entire
+         * Behavior just to have it constantly transform an object.
+         *
+         * There are three predefined behaviors:
+         * - Behavior.simpleTranslation -- constantly translates a game object by the amount specified
+         * - Behavior.simpleRotation -- constantly rotates a game object by the amount specified
+         * - Behavior.simpleScale -- constantly scales a game object by the amount specified
+         *
+         * For this example, we'll just use simpleRotation. */
+
+        Polygon2D premadeBehaviorsBox = Polygon2D.create(DrawUtil.createBox(500f, 500f, 50f), RenderStyle.FillAndOutline)
+                .withFill(Color.red)
+                .withOutline(Polygon2D.DefaultOutlineStroke, Polygon2D.DefaultOutlineColor)
+                .build();
+
+        premadeBehaviorsBox.addBehavior(Behavior.simpleRotation(3f), this);
+        drawableManager.addGameObject(premadeBehaviorsBox);
+    }
+
+    @Override
+    public void update(Display display) {
+        // Empty -- this example does not make use of this method.
+    }
+
+    public static void main(String[] args) {
+        FastJEngine.init("Hello, FastJ Behaviors!", new Main());
+        FastJEngine.run();
+    }
+}

src/example/java/tech/fastj/example/behaviors/SimpleMovementBehavior.java

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+package tech.fastj.example.behaviors;
+
+import tech.fastj.engine.FastJEngine;
+import tech.fastj.math.Pointf;
+import tech.fastj.graphics.game.GameObject;
+
+import tech.fastj.systems.behaviors.Behavior;
+
+public class SimpleMovementBehavior implements Behavior {
+
+    /* Behaviors (any class which implements the Behavior interface) have a few useful methods:
+     * - init(), which takes in the GameObject that uses the behavior and is called when the
+     *   behavior gets initialized (usually right after the GameObject gets initialized).
+     * - update(), which takes in the same GameObject that is provided in init() and is called
+     *   after every SimpleManager/Scene update() call.
+     *
+     * You'll get to know these methods inside and out with time. */
+
+    private String gameObjectId;
+
+    @Override
+    public void init(GameObject gameObject) {
+        /* Since this will only be called on first initialization, we can use it to accomplish
+         * initial actions.
+         *
+         * In this case, we'll simply change the game object's translation to (50, 50). Since
+         * translate(Pointf) is available to all GameObjects, this is general enough to be applied
+         * to any sort of GameObject that could be used with this Behavior. */
+
+        gameObject.translate(new Pointf(50f, 50f));
+
+        /* We'll also log that the behavior has been initialized, to get a sense of when this
+         * method is called. While doing so, we'll keep track of the game object's id for later
+         * usage. */
+        FastJEngine.log("SimpleMovement behavior for GameObject " + gameObject.getID() + " has been initialized.");
+        gameObjectId = gameObject.getID();
+    }
+
+    @Override
+    public void update(GameObject gameObject) {
+        /* Since this will always be called right after the update() call on the
+         * SimpleManager/Scene, we can use it to accomplish repeated actions.
+         *
+         * In this case, we'll rotate the game object by 5 degrees every time the method is called.
+         * Since rotate(float) is available to all GameObjects, this is general enough to be applied
+         * to any sort of GameObject that could be used with this Behavior. */
+
+        gameObject.rotate(5f);
+    }
+
+    @Override
+    public void destroy() {
+        /* You can also implement this method -- destroy().
+         * When the behavior's game object is destroyed, the behavior gets destroyed as well. You
+         * can choose to include specific behavior for when the behavior is destroyed using this
+         * method. */
+
+        /* First, we'll log that the behavior was destroyed using the gameObjectId we kept from
+         * before. */
+        FastJEngine.log("SimpleMovement behavior for GameObject " + gameObjectId + " has been destroyed.");
+
+        /* Now that the id is no longer used, we'll set the gameObjectId we kept from before to
+         * null. */
+        gameObjectId = null;
+    }
+}