Descending Doom 81

[Descending Doom 81] ----------------------------------------------------------

BY L.PIERI (https://lupoman.itch.io/)

A ZX81 conversion from the Hare Basic original by Robin of

8-Bit Show and Tell (

)

To be compiled in Z88dk:

   zcc +zx81 desdoom81.c -create-app 

I love the prototype Robin made to test out Hare Basic and decided to port it

to the ZX81. I'm a fan of his youtube channel.

Sadly basic is to slow, the cpu uses a lot of time to draw the screen on the 

tv. 

So I ported it to C which is very fast if you know the quirks of Z88dk and the

ZX81.

The code is as simple as it gets, it could be simplified (and optimized) but 

I think its quite easy to read and follow most of Robin code most of the time.

I didn't implement the step motion (directions+fire) because its cumbersome

in the ZX81 keyboard, and I don't have a routine to read more than one key if

it is possible on this machine.

The Hare Basic code is very efficient and small.

I made a couple computations before hand to save some 16 bit multiplications

(Z80 doesn't have a multiply instruction, least a 16 bit one)

I added some #define to help with some constants.

I use a notepad and .bat in order to compile and launch the emulator automatically

not much else.

I hope someone will find this included source code usefull and the litle game

fun to play.