Sid Spanners

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by Digital Prawn 26th December 2010



Platform: ZX Spectrum 48K



KEYS

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LEFT - O

RIGHT - P

JUMP - Q/Z/M



Instructions

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Guide Sid Spanners through eight levels of platform mayhem,

unscrewing nuts (small white circles) as you go.

Simply touching a nut causes it to unscrew.

When all nuts on the level have been unscrewed, the door 

will activate and start to flash. Exit via the flashing door

to complete the level. 



Each level contains four lethal guardians which must be avoided.

You start the game with four lives. There's also a fixed timer

on each level which counts down from 100. If the timer runs out,

then the game immediately ends regardless of how many lives

remain, although the time limit is very generous.



Complete all eight levels to win the game.



Thanks

------

Thanks to the creators of Z88DK, the SP1 library and all of the 

other libraries used in this game. Thanks also to all 

World of Spectrum forum members who replied to my questions in

the "Development" thread. Too numerous to mention everyone who

made this game possible, but all of your useful information

helped. In particular aralbrec's sprite example, Timmy's pointer

to the info on implementing the U_malloc() function used by the

SP1 sprite libraries. Alcoholic's Anonymous for developing the

Z88DK system, na_th_an's Spritepack notes, metalbrain's

jump key suggestion and also for creating SevenUP... Thanks to

Martijn for uploading the game to the WoS archive etc... etc...



Developer Notes

---------------

This is my first program to use the excellent SP1 sprite library

for Z88DK. Originally written as a simple test program just so I

could get some sprites moving around the screen, it started to

look like a playable game just after a couple of evenings of

tinkering. When I got the jump action of the player sprite

refined, it just seemed so much fun to jump around the screen.

So I went ahead and proceeded to finish this simple game.



Running out of RAM was the main problem encountered as the level

data set is coded in a memory-inefficient (but easy to work with)

format. Each level description takes up 0.5KB of space and is a 

simple 2D character-map description of the level. However,

with some form of compression, or an alternative representation

more suited to a "sparse array", I'm sure a lot more levels

could be fitted in.



This game has just under 1KB of space remaining, so theoretcally,

one more level could just about be shoe-horned in without changing

the code. I had to repeatedly reduce the size of the heap (used by

the sprite library) and the space allocated to the z80 stack just

to fit the ever-expanding program code in. Also the progam uses

a replacement ISR in IM2 mode which does nothing, simply to

prevent the ROM ISR from clobbering something used by this

program and to speed it up. IM1 mode does crash this game though,

although I never investigated exactly why that is. Also, the

game does do a lot of stuff in contended memory, which no doubt

does slow it down a bit, but given the tight memory constraints,

it's seemingly impossible to avoid. Compiled C code tends to fill

up the RAM quite quickly, but I never got round to attempting to

optimise this program for space - although I'm sure there is room

for space savings by tweaking the code a bit.



It's very easy to take the source code of this game and just create

an alternative level set by changing the level data. Or even the 

sprite and tile data can easily be replaced. It's all in 

the public domain.