Where have all the aliens gone?

From Richard's C64 blog!

14th March 2020

Great news. Cruiser-X 79 continues this month. Today has been quite a long session. You might probably notice that the game was delayed for a very long time over several months period. This was mainly because of some other game projects I was working on. Happy Blocks DX, Amazon Tales, Mega Tank Blasta, Toxic (2020 Edition). Amazon Tales was made as a practice piece in order to attempt to develop custom enemy movement patterns which didn’t require wasting $200 bytes of data. Plus I wanted to add a mixed batch of enemies in to the game project.

Since the game engine in Amazon Tales was successful. I have decided to try a similar attempt for Cruiser-X 79. In order to do that. I have to start the enemies attack patterns from scratch. Before I could do that, I had to delete the existing alien attack patterns. Therefore on today’s build of the project, I concentrated on setting up table values per enemy type.

For example:

Alien1SpawnX = The starting horizontal position for the alien to spawn from
Alien1SpawnY = The vertical horizontal position for the alien to spawn from
Alien1Dir = Direction for the alien to move whilst in operation. 0 = Up, 1=Down, 2=Left,3=Right. This consists of a table of 8 bytes (Since the aliens are supposed to switch to the next direction every time a path limit has been reached).
Alien1Speed = Speed of the alien which is moving, once again 8 bytes.
Alien1ChangePosition = Horizontal or Vertical position in which the alien must reach before it can change to the next direction (or leave the screen)
Alien1ObjectLo = Low byte of the animation frame read from the sprite animation subroutine
Alien1ObjectHi = Hi byte of the animation frame read from the sprite animation subroutine
Alien1Colour = Alien sprite colour
Alien1Lives = Amount of lives the alien has before it can be destroyed
Alien1Score =  Multiple number of points to be scored per alien destroyed

I also made different lo/hi byte tables which should somewhere in the game code (once implemented) copy the self-modifying pointers in to the correct self-modifying code. For example, after the last change position has been breached, and all aliens are off set. A new group should spawn.

For now, there’s no aliens in this current build, because the code needs to be started from scratch. This will be continued during my next coding session on this game project.

Original URL: https://tnd64.blogspot.com/2020/03/where-have-all-aliens-gone.html