If you got a bit lost anywhere along the way, you can download my files for part 5 here:
Feel free to download these and use them to get going again.
We’re going to add some bad guys now. First things first, we need a way to set the position of a sprite on the screen.
Add these two simple methods to the Sprite class:
// Sprite.java
public void setPosition(int x, int y) {
this.x = x;
this.y = y;
}
public void movePosition(int x, int y) {
this.x += x;
this.y += y;
}
Hopefully they should be self explanatory, but just in case, one sets the position to a place on the screen, and the other moves the position by an amount we give it.
Cool.
Next.
We’ll create a list of baddies in each lane, so we need to import the List classes and create a variable for the first lane:
// JDojoMaster.java
import java.util.List;
import java.util.ArrayList; // Add these at the top where they go
public class JDojoMaster extends JFrame {
static final long serialVersionUID = 0;
protected Scene scene;
protected Sprite player;
protected Spritesheet spritesheet;
protected GameController controller;
protected List<Sprite> north_lane = new ArrayList<Sprite>(); // This is new
public static void main(String[] args) {
so the list north_lane will hold all the baddies that come as us from the north of the little cross we made before. Now add some code to the gameloop() method:
// JDojoMaster.java
public void gameloop() {
long timer;
long update_timer = 120; // this is new
while (true) {
timer = System.currentTimeMillis();
if (controller.up) {
player.setImage(spritesheet.getTile(1));
}
if (controller.down) {
player.setImage(spritesheet.getTile(0));
}
if (controller.left) {
player.setImage(spritesheet.getTile(3));
}
if (controller.right) {
player.setImage(spritesheet.getTile(2));
}
// code below here is new
update_timer -= 1;
if (update_timer == 0) {
north_lane.forEach((s)->s.movePosition(0, 32));
Sprite enemy = new Sprite(spritesheet.getTile(8));
enemy.setPosition((256/2)-16, 16);
north_lane.add(enemy);
scene.addSprite(enemy);
update_timer = 120;
}
scene.repaint(); // not new :)
So, each time around our loop, we decrement a counter - our loop runs every 16.6 milliseconds, because of the Thread.sleep() call below where we just added this code. Each time update_timer gets to zero, we reset it to 120. 120*16.6 is about 2 seconds (don’t worry, this took me a couple of minutes to work out why it was going so slowly when I had it waiting for 1200 each time!).
Every 2 seconds a new enemy will spawn at the top of the lane. All the other enemies will also move down a step in the lane because we call move_position() for each one in the forEach loop.
Try it.
It’s not a game yet, we’re taking things slowly at this stage as things get complicated. In the next part we’ll choose a random lane to add a baddie to each update loop.
Last little bit, if you haven’t done it already, add this to the JDojoMaster.java init() method, just beneath where you create the player sprite:
// JDojoMaster.java
player.setPosition(128-16, 128-16);
Look out, they’re comin’ for ya!