( click for download, now version 0.8 from 25nd Jan)

My intial waffle on the subject.

Version 0.5 discussion

So far in version 0.6:
Period of invincibility for new ships.
Slow armour repair as standard.
Player drops cash when killed (at the moment does not leave the screen)
Added a 4th level.
Twinshot is now cheaper and includes several levels of ROF to compensate.
Burst is now cheaper and includes a level of Damage to compensate.
ROF is now purchased in lumps of 2.
Shop now appears as an object you can fly into.
Ground friction to compensate for inertia (also makes jumping more useful)
Auxillary guns now added: We have a Hyper-shot (fast but may ricochet), Vulcan cannon and Wide shot.

Things I may alter: There will soon be too much choice in the shop, so I will either break these down into specialist shops (energy/body-shop; blaster shop; Special shop)
or restrict what is available (with discounted items and out-of-stock items)

New for version 0.7:
Vulcan is now fully automatic. Wide shot can reduce the size of oncoming enemy bullets.
Shop has changed - now gives you a random selection of 10 items (one of which is 'EXIT', though).
All add-ons and guns have a rarity value; so now we can put in 'ultra rare' items as suggested by Derek.
Also Derek's suggestion of numbering the items for allowing quick access is in there. Also cost is displayed under the item.
Finally, experimentally, I have removed collision damage (as it seems to be to common a cause for death) and replaced it with score reduction. Think of this as a repair charge for the player :> and it figures into an aliens fitness score.

So far in version 0.8:
New auxillary weapon: Rockets.
Tidier level select screen. Still immensely crap though.
Collision detection is a bit better.
We now have end-of-level baddies. And the levels end.
1/10th of all money earnt goes to a "Retirement Fund", i.e. the final score.

Version 0.81:
Added 'coolant gel' addon to aid ROF for multiple guns / high damage.
Added Homing addon for special shot. (Mostly works well; sometimes they seem to veer wildly off course)
New Vulcan sound. Rockets fire in salvos of 3 now, not 4.
Initial special charge is now proportional to mass, so little aliens fire little special shots; End-of-level baddies will be more dangerous.
Streak bonus multiplier; so more cash now available in the shop.
Your ship doesn't degrade when a level is finished, now.

Derek's Comments:

Laser is ace. It's a heck of a lot faster now. Possibly too fast on my machine at home. Speed limiter possible?

However:



This happened whilst I was on the space level which wasn't going too well. At first most of the aliens weren't bothering to come down the screen.
They went back up and died. If they appeared at all. After this they tended to just sit there and do nothing.
I was firing a laser at them when it crashed.

Sort the shop speed out! It's still really unresponsive in the shop. I press a key, nothing happens. I often have to press several times to achieve anything.

The innertia on the moon is a bit crap really. Just because it's what would be likely to happen is no excuse to have it. It just takes away the ability to aim at the aliens.
Remember Amiga Power's feeling on Slippy Slidey Ice Worlds?

Other than that it's going fairly well.

Duncan: Thanks for your feedback!; I'm glad the optimisation has worked. I think I can set the frame rate for a specific value.
The crash is probably a divide-by-zero thing or I'm accessing an array incorrectly; i don't think it's laser related but I will investigate.
I will look into the shop next :>
I will continue to experiment with friction/air resistance/thrust settings to find a happy medium (or a jolly psychic)