JUNE 2019

Chapter 17 -  Killing Aliens


For this chapter, I have added the collision detection routine which checks to see if any of your missiles has hit an Alien and accordingly blows it up, accompanied with a rewarding explosion sound as the Alien disintegrates into many fragments.

Also, you may collect extra Takium charge required by your Gunstar by shooting the glowing BLUE objects. Your Takium charge will slowly be depleted with every strike by the Alien's missiles or direct collision. When the charge reaches a dangerously low level, an alarm will sound warning you to collect more Takium.

Shooting the glowing RED objects will add charge to your Fusion bomb. When you fully charge your Fusion bomb, the nose cone of your Gunstar begins to spin indicating that your bomb is ready to be detonated when needed. This will destroy all Aliens on the screen with a single blast.

Now that more of the game is starting to come together, I have been able to activate more of the sound effects that I created back in Chapter 3. They have been sitting idle in the background waiting to be summoned. Listen to the Video Blog below and you will hear the audio mayhem that the game holds. No sound chip, just the standard 6-bit DAC built in to every CoCo.


The graphics I created for the explosion effect were firstly designed using a 2D graphics editor on my Amiga.  I was able to experiment with particle layout as well as determine graphics which didn't place too much burden on the CoCo's CPU.

Once, I created a set of sequential frames that I was happy with, I wrote the code that would draw the graphics as a compiled sprite. Almost all the sprites in GunStar are compiled sprites for speed.

I restricted the pixels used in the explosion to be 2 pixels (1 byte) wide. This is faster to work with and avoids the need to preserve adjacent pixels. 

The program has been set to manage a maximum of 10 Alien and Object sprites on a screen. I will also allow for a number of Alien missiles to be fired that your GunStar must avoid. I've yet to determine how many should be fired as a maximum since I don't want the screen to be too congested making the game too hard.

Destroying an Alien also awards a score which is displayed overlayed in the top left of the screen.




Click on the YouTube link below to see the actual game so far.


Video Blog #6


For the next chapter of the GunStar Development Blog, I will make the Aliens fire back at me. Then the game begins to get more challenging!




Copyright 2017 by Nickolas Marentes