Machine code analyis: Froggie 1983 game

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David G
Posts: 387
Joined: Thu Jul 17, 2014 7:58 am
Location: 21 North, 156 West

Machine code analyis: Froggie 1983 game

Post by David G »

Froggie (1983) has some interesting code -- and is a topnotch ZX81 game too. Froggie (1983) by Richard Braunton

* Transitions between screens. Simple code, but very effective. See sample code in Transition Effects Code

* Press A Key prompt animation screen at USR 22477
press-a-key.JPG
press-a-key.JPG (9.28 KiB) Viewed 1483 times
* Goodbye display text effect at USR 18413
goodbye.JPG
goodbye.JPG (8.41 KiB) Viewed 1487 times
It appears to use a traditional game loop (of many, many subroutine Calls). It also demonstrates how to detect keypresses (e.g. see address $4D46).

Attached is an Assembly Language file for the game in ZX-IDE format.
Attachments
froggie-1983.zip
froggie-1983.asm
(8.82 KiB) Downloaded 136 times
David G
Posts: 387
Joined: Thu Jul 17, 2014 7:58 am
Location: 21 North, 156 West

Re: Machine code analyis: Froggie 1983 game

Post by David G »

The Goodbye routine uses standard graphics characters placed in REM 8.

I wonder how he originally created this text -- with a special tool, or simply by trial-and-error on a the ZX81 keyboard?
Goodbye-REM8.JPG
Goodbye-REM8.JPG (14.91 KiB) Viewed 1482 times
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