Cruiser X-79 – Update #8

From Richard's C64 blog!

20th-24th June 2017

It has been too hot this week, apart from yesterday and today. Despite the really hot UK weather I had recently, still that hasn’t stopped  me from doing more on this game project. Quite a big update as well.

So then what has been happening this time round. For a start off I continued from a couple of weeks ago. This was where code was based on sprite / background collision. I originally worked on a subroutine where the player crashed should it hit a deadly character. Now this time I focused on the player bullet shooting to deadly background. I tried doing the bullet/background table read method, but that didn’t quite work out. There were times where the player bullet kept on missing the deadly background and the bullet just flew over. A bit of additional hard work was required to this. I created a large listing to compare to a certain character to the bullet object position. If the central bullet reaches the deadly background, the bullet will disappear. Thus allowing the player to fire again. After testing this phase, things looked much better.

The next step was to do a little something different. I worked on the new title music for the game, using GoatTracker. I was unable to combine the title music with the other sounds, as there was a memory overlap. So I trimmed out the title music and placed it into a separate position and put it in the temporary preview title screen. I also programmed built in option where using a joystick in port 2 selects the sound mode (Music + SFX, Music Only, SFX Only, Silence).

Today I have been working on fixing some of the bugs in the game, and also adding some additional sprites. The sprites which represented Game Over and Stage Complete. In the stage complete phase, the player ship is automatically central before the Level Complete message appears on screen. During the player moving or the game over scene, all sprites get switched off, then after fitting the Game Over, Well Done screen, only 2 sprites are switched on.

The main game had some problems with the alien formation test. There were aliens that appeared incorrectly on screen while moving. I had forgotten to update offset code to reset the formation counter, so that aliens started in the correct position. After trying the game out, things looked very promising indeed. That was until, I came across the camel head aliens. They were flickering everywhere instead of using a proper formation. I managed to fix this problem by updating the low+hi byte tables for alien formation and properties. I tested the whole thing again and things looked a whole lot better.

As my final task today. I took a look at IRQ source code and tried to implement some subroutines. Reason being – The aliens and laser sprites were still visible over the black raster, that covers the scrolling background. In order to fix this problem, I altered the background colour to black (So no grey raster line could be seen). Then after that, a new subroutine was added to mask existing sprites as blank sprites. The trick worked, and the result was pretty good – although there is a minor glitch inside the score panel raster. It flickers for a split millisecond, but all in all, the game is playable.

Still no selected alien formation for each level yet, but that will be happening some time soon. Enjoy the latest video of what has been resulted this week.

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