My next game is based partially on the old Atari 8-bit game Caverns Of Mars. While this had no real enemy moving objects as such, everything that was shootable moved up the screen (along with the scrolling background). I could have just scrolled these as part of the background but I wanted to animate them in the future so I needed to run some tests. For accuracy of the tests, it was time to dig out my Amiga A1200.

Caverns of Mars - The original version

My version - so far

Well, it's been so long since I actually used my real Amiga, I rearranged my room so that my PC and Amiga are side by side. This is much better for programming as before I had to go to a different room to try my games on a real Amiga. And also the VBLANK of the emulators and also certain displaying problems mean that I should really test my code on my A1200 also!

What I did today was the groundwork I needed for future projects. I needed to see how many things I could blit onto the screen smoothly in sixteen colours using Blitz Basic. I was using the bob erasing QBLIT command as a buffered (background replacing) BBLIT is a hell of a lot slower.

I wrote a small program to scroll 16x16 16 colour blocks up a double buffered screen from random positions and move them to the bottom of the screen when they reach the top. On this initial test, on my A1200 using an A500 compatible graphics library, I found that I could blit just over 40 blocks on the screen and maintain a perfect 50hz screen update.

Now there is probably very little likelyhood of me ever needing this many (I'd be surprised if I ever used more than 20). But with the added overhead of game code, music, harware sprites and scrolling this value will be reduced slightly (dependant on game of course!). I should be OK.

I didn't include the source for this routine because I crashed the Amiga before saving it. Theres another thing which should never be done but so many programmers do lose code before saving. God knows how many times it's happened to me!

Next, I'll try hardware vertical scrolling of a double buffered screen.

STOP PRESS. - Incorporating another of my favourite Atari 8-bit games into this one. Stella Shuttle which was based on the old Lunar Rescue arcade machine. As this gameplay can be easily inserted into the original plan and the extra coding is minimal. Hopefully, this game will surface!!!

Diary 2.2 October 15 1999

Well, my game design is coming along rather nicely. Originally planned to be 16 colours. I am now using an 8 colour on 8 colour dual-playfield (for lovely parallax scrolling) with a 16-colour 32 pixel wide sprite for the main ship. This should leave 4 harware sprites for bullets, score etc.

The game is also A500 compatible. I know, this seems like a bit of a backward step but it's just that this is meant to be a simple game and I find that coding for A500 is much easier in Blitz. Also, because I have to draw the GFX myself, I've found that the less colours there are, the better my drawings look. So there!

Besides that, the game is being written entirely on the PC under WinUAE and Fellow. So as Fellow doesn't do AGA and WinUAE has problems emulating AGA so far, it had to OCS. So what have I done.

Right, well a lot of the graphics have been completed and cut into nice little 16x16 blocks for the map editor. Now usually, when I write a game, it all falls to pieces when I have to write the map editor so this time I am using Liz Tucker's BlitzMap (available from the Aminet). It was pretty easy to use and saves all the files I need ie. Map Data, blocks, palettes and special effects if needed. I created a simple test map based on my initial graphic blocks and my first test in blitz was to get a nice parallax scrolling screen with the main ship on top.

As you can see from the grab, it's starting to look rather good. Here, take a look at the original XL game screen.

And Here is how my version is shaping up...

You have to admit, it is starting to look like a game now! See you soon.

Coagulus / Rob.