EntityDemo.java

// EntityDemo.java

package examples;

import static org.lwjgl.opengl.GL11.*;

import org.lwjgl.input.Mouse;
import org.lwjgl.opengl.*;
import org.lwjgl.*;

import entities.AbstractEntity;
import entities.AbstractMoveableEntity;
import entities.Entity;
import entities.MoveableEntity;

public class EntityDemo {

    private long lastFrame;

    private long getTime() {
        return (Sys.getTime() * 1000) / Sys.getTimerResolution();
    }

    private int getDelta() {
        long currentTime = getTime();
        int delta = (int) (currentTime - lastFrame);
        lastFrame = getTime();
        return delta;
    }

    private static class Box extends AbstractMoveableEntity {

        public Box(double x, double y, double width, double height) {
            super(x, y, width, height);
        }

        @Override
        public void draw() {
            glRectd(x, y, x + width, y + height);
        }

    }

    private static class Point extends AbstractEntity {

        public Point(double x, double y) {
            super(x, y, 1, 1);
        }

        @Override
        public void draw() {
            glBegin(GL_POINTS);
            glVertex2d(x, y);
            glEnd();
        }

        @Override
        public void update(int delta) {
            // Do nothing
        }

    }

    public EntityDemo() {
        try {
            Display.setDisplayMode(new DisplayMode(640, 480));
            Display.setTitle("Entity Demo");
            Display.create();
        } catch (LWJGLException e) {
            e.printStackTrace();
        }

        // Initialization code Entities

        MoveableEntity box = new Box(100, 100, 50, 50);
        Entity point = new Point(10, 10);

        // Initialization code OpenGL
        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        glOrtho(0, 640, 480, 0, 1, -1);
        glMatrixMode(GL_MODELVIEW);

        lastFrame = getTime();

        while (!Display.isCloseRequested()) {
            // Render

            point.setLocation(Mouse.getX(), 480 - Mouse.getY() - 1);

            glClear(GL_COLOR_BUFFER_BIT);

            int delta = getDelta();
            box.update(delta);
            point.update(delta);

            if (box.intersects(point)) {
                box.setDX(0.2);
            }

            point.draw();
            box.draw();

            Display.update();
            Display.sync(60);
        }

        Display.destroy();
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        new EntityDemo();
    }

}

// Entity.java

package entities;

public interface Entity {
    public void draw();
    // See episode 7
    public void update(int delta);
    public void setLocation(double x, double y);
    public void setX(double x);
    public void setY(double y);
    public void setWidth(double width);
    public void setHeight(double height);
    public double getX();
    public double getY();
    public double getHeight();
    public double getWidth();
    public boolean intersects(Entity other);
}

// MoveableEntity.java

package entities;

public interface MoveableEntity extends Entity {
    public double getDX();
    public double getDY();
    public void setDX(double dx);
    public void setDY(double dy);
}

// AbstractEntity.java

package entities;

import java.awt.Rectangle;

public abstract class AbstractEntity implements Entity {

    protected double x, y, width, height;
    protected Rectangle hitbox = new Rectangle();

    public AbstractEntity(double x, double y, double width, double height) {
        this.x = x;
        this.y = y;
        this.width = width;
        this.height = height;
    }

    @Override
    public void setLocation(double x, double y) {
        this.x = x;
        this.y = y;
    }

    @Override
    public void setX(double x) {
        this.x = x;
    }

    @Override
    public void setY(double y) {
        this.y = y;
    }

    @Override
    public void setWidth(double width) {
        this.width = width;
    }

    @Override
    public void setHeight(double height) {
        this.height = height;
    }

    @Override
    public double getX() {
        return x;
    }

    @Override
    public double getY() {
        return y;
    }

    @Override
    public double getHeight() {
        return height;
    }

    @Override
    public double getWidth() {
        return width;
    }

    @Override
    public boolean intersects(Entity other) {
        hitbox.setBounds((int) x, (int) y, (int) width, (int) height);
        return hitbox.intersects(other.getX(), other.getY(), other.getWidth(), other.getHeight());
    }

}

// AbstractMoveableEntity.java

package entities;

public abstract class AbstractMoveableEntity extends AbstractEntity implements MoveableEntity {

    protected double dx ,dy;

    public AbstractMoveableEntity(double x, double y, double width,
            double height) {
        super(x, y, width, height);
        this.dx = 0;
        this.dy = 0;
    }

    @Override
    public void update(int delta) {
        this.x += delta * dx;
        this.y += delta * dy;
    }

    public double getDX() {
        return dx;
    }
    public double getDY() {
        return dy;
    }
    public void setDX(double dx) {
        this.dx = dx;
    }
    public void setDY(double dy) {
        this.dy = dy;
    }

}