Creators – Shootah Part 3 – Enemies etc.

This week we continued our Shootah project. We did two main things;

  1. Changed the code to control the total number of bullets to those actually on screen
  2. Added an enemy that loops backwards and forwards across the screen

Controlling the Number of Bullets

In Part 2, we made a new bullet every time the user pressed the Up key and put it in the bullets list.

This meant that after a while we could have a lot of bullets, most off the top of the screen, which was even slowing some machines down.

To limit the number of bullets we did four things:

  1. Added a new property to the Bullet class called active and set it to be true
  2. In the move() function for the bullet class, we added a check for the bullet going off the top of the screen (this.y < 0) and, if true, set the active property to false
  3. In sketch.js, we moved the lines of code in the draw() function responsible for moving and drawing the bullets into a new function called manageBullets() and called it from draw().
  4. In manageBullets() we made a new list called active and put every bullet that was still active into it. We then made this the new bullets list.

We write a little code that printed out the total number of bullets to verify this was working.

Adding an Enemy

We added a new file called enemy.js and included it in the index.html file.

This file looked a lot like player.js. The main different was the move() function. Our enemy moves constantly left-to-right. When it gets too far off the right-hand side of the screen (checked in move()) we set its x position to be off the left-hand side of the screen instead. This makes it loop around.

TODO

We still have loads to do and we made a list on the day:

  • No more infinite bullets!
  • Check edges so spaceship doesn’t disappear
  • Enemies
  • Collision detection
  • Enemies shoot back (bombs)
  • Lives/score
  • Levels
  • Background music
  • Moving background
  • Story

We’ve done two and we’ll do some of the others for sure.

Download

The files for this week can be found on our GitHub repository.

 

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