OCC is an unofficial open source engine reimplementation of the game trilogy Crystal Caves.

Download binaries and project info at itch.io

This repository includes the shareware version of Crystal Caves. To play the full, retail version, you can copy over the data files or purchase them at Steam or GoG.

Current state of OCC:

Currently the engine can:

• Load sprite, item and level data.
• Play through a few levels.
• Some enemies, hazards and items.

Features that are missing:

• Loading and saving games.
• Some items.
• Some enemies.
• (and much more).

OCC aims to be a better, modern remake of Crystal Caves while preserving the same gameplay experience. Therefore there are some changes and improvements made where they make sense. Below is a list of differences:

Feature	Crystal Caves	OpenCrystalCaves
BBS menu item	"Call our BBS" menu item which shows BBS phone numbers	"Visit our Website" which opens the browser to the OCC game page
Earth and moon orbits	Earth and Moon move at constant speed	Earth and Moon move in a circular arc
Enemy and hazard detection	Detection can go through walls	Detection is blocked by walls
Head bump momentum	Horizontal momentum is lost when player bumps their head	Horizontal momentum is preserved when player bumps their head
Instructions	Sequential, text-only instructions	Added inline icons showing what game objects look like
Laser position	Laser is fired slightly below the muzzle	Laser is aligned with the muzzle
Moving platform animation	Animation is the same regardless of direction	Animation reverses so that monitor follows background
Question mark spin animation	Animation repeats and skips some frames	Animation shows fully rotating question mark
Quit To OS menu label	Quit to DOS	Quit to OS depending on build
Restarting levels	Menu > Quit Current Game > Main Level, re-enter level	Menu > Restart
Transitions	Fade by palette color	Fade to black
Hammer crush	Getting hurt normally by hammers	Getting crushed by hammers
Candle pickup sound	No sound	Same sound as other similar pickups (shovel, pickaxe)
Snoozer roll animation	Third frame has slight Y offset	No irregular Y offsets
Flame on/off animation	Transition in but not out	Transition both in and out
Lights off	EGA palette swapped	Option to use blue monochrome dark palette
Level complete indicator	Green overscan (invisible in dosbox)	Flashing green screen border
Red mushroom	Timer in status bar	Player pulses red
Stopped enemies	Stopped bar	Stopped and blinking red
Falling rocks	Can spawn outside danger area	Only spawns in danger area
Stopped platforms	Animated	Not animated
Slime and egg positions	Strictly aligned with tile grid	Dynamic position based on parent
Enemy destructible shots	Stops shooting if shot goes off screen	Keeps shooting

OCC is built using C++20 and requires external libraries: SDL 2.0, and SDL_mixer. SDL2 must be installed and available in /usr/include/SDL2. Additionally the build system cmake must be installed.

Steps to compile (Linux, macOS):

git clone --recursive https://github.com/gurka/OpenCrystalCaves.git
cd OpenCrystalCaves
mkdir -p debug
cmake -Bdebug -DCMAKE_BUILD_TYPE=debug occ
cd debug
make

The binary will be available at OpenCrystalCaves/debug/build/occ

Or in Windows (with vcpkg):

# In vcpkg dir
./vcpkg install --triplet x64-windows sdl2 sdl2-mixer --recurse
# In your projects dir
git clone --recursive https://github.com/gurka/OpenCrystalCaves.git
cd OpenCrystalCaves
cmake -Bbuild -DCMAKE_TOOLCHAIN_FILE=C:/path/to/vcpkg/scripts/buildsystems/vcpkg.cmake occ -A x64

The Visual Studio project will be available at OpenCrystalCaves/build

OCC includes the shareware episode for convenience, but for the other episodes requires data files from the original Crystal Caves (any episode). Either install it via Steam or GoG, or copy the game data to the media folder in the occ package (such as CC1.GFX).