Build a complete ZX Spectrum game in Z80 assembly, one playable step at a time.
Under the hill of Morrow lies a crypt older than the village. Torches burn in its halls though nobody has lit them for a thousand years, skeletons still walk their rounds, bats hang in the dark, and the gate closes behind you: it opens again only for whoever brings back three lost seals. Cryptmorrow is an original dungeon explorer for the ZX Spectrum, and this book shows you how to build it yourself, from the first room on the screen to the finished game on tape, with its title, its music and its endings.
The complete game is yours. A companion repository on GitHub holds the full source code of Cryptmorrow under the MIT license: the finished game, the eight steps of the book, 22 ready-made experiments, the automated tests and the tools, and the game ready to play on tape. The address is printed in the book.
What you will build
- Sixteen rooms in an atrium and three zones, each with its own colours, drawn from tiles, with flickering torches
- An explorer drawn as a masked software sprite, who walks, stops at walls and swings a blade
- A HUD with energy, keys, seals and a six-digit score
- Keys, locked doors, treasures, potions and three seals that open the way out
- Skeletons that patrol and bats that give chase, with damage and GAME OVER
- Music on the AY chip of the 128K and sound effects on the beeper of the 48K, with a MUSIC, SOUND FX or SILENT menu and Kempston, Sinclair or keyboard controls
- A title in big letters, victory and defeat screens, and a tape with a loading screen and a packed program that unpacks itself at the start
How this book teaches
- No assembly experience needed. The book starts from the first instruction and explains every one it uses.
- Eight playable steps. Each is a complete program cut from the finished game, so nothing you learn is thrown away; its SHA-256 fingerprint tells you that you built exactly the program in the book.
- The hard parts of the Spectrum, explained. The screen's memory layout, attribute clash, contended memory, IM 2 interrupts, the beeper, the AY chip, the tape and its loader.
- Real code, real screens. Every listing is checked line for line against the source you download, and every screen of the game in the book is captured from the running program, nothing drawn or retouched.
- Make it yours. 14 guided experiments change speeds, colours, keys, damage, music and more, with the allowed values and the way back.
- Where it breaks. 8 classic mistakes made on purpose and explained.
- Measured, not guessed. T-states, contended memory and loading time are measured in a test bench, and automated tests play the game a frame at a time, comparing every screen byte for byte with a model of the game.
- A reference chapter on reading and checking the whole game, a glossary of 91 terms and an index.
Inside the book
Your workshop - The Z80, memory and the screen - The tile engine - Text, torches and the frame - Software sprites - The explorer - The dungeon and the HUD - Objects, doors and the portal - The enemies - The blade and the damage - The AY and the music - The beeper, the effects and the sound modes - The title and its big letters - States, menu and end screens - The tape - Reading and checking the game
What you need
A computer and three free programs: the sjasmplus assembler, the Fuse emulator and Python. The game runs on the 48K and the 128K Spectrum and was tested in emulation.
Cryptmorrow is the first volume of the ZX Spectrum Game Manual Series, where every book is independent and brings a new original game to life. Load the tape, step through the Moss Gate and find the three seals.
