[>]monad-engine

monad is a small C++17 engine I wrote to learn how game engines fit together. It started alongside a lesson series on engine programming and kept growing after that, until it ran a first-person sandbox with a sword, a carbine and an enemy to use them on.

##What's in it

• OpenGL 3.3 core renderer. Game code submits mesh and material pairs to a render queue, and the engine draws them after the update.
• A pixel-art post-pass based on the three.js pixelation example: color, depth and normal samples snap to a grid, with optional depth and normal edge outlines. Debug views show the raw depth and normals.
• Scenes as JSON files of game objects and components: camera, mesh, light, physics, audio, health, particle emitter, player controller, animation and skinned mesh. A game adds its own types with the GAMEOBJECT and COMPONENT macros.
• Bullet for rigid bodies, a kinematic character controller, raycasts and contact callbacks.
• glTF through cgltf. FBX and OBJ through Assimp, including skeletons up to 128 bones and animation clips skinned on the GPU.
• Positional audio through miniaudio.
• Particles, plus a sprite and text renderer used for the FPS counter.
• A Dear ImGui editor on F1 with hierarchy, inspector, console and stats windows, and tabs for render, physics and player settings. Games can add panels to it.

##The sandbox

source/ is the game that runs by default. It loads scenes/testing.json: a player, an enemy, a jump platform and about 40 physics bodies. 1 picks the sword and 2 the carbine. Left click shoots or swings, right click blocks.

The game adds editor panels of its own: one to reseed and test its RNG streams, one listing every health component with damage, kill and revive buttons, and one for raycasts.

##About Vulkan

There is no Vulkan renderer. engine/source/graphics/vulkan/ holds a separate preview program that creates a device, a swapchain and a render pass, then clears the window to a slowly shifting color. It is kept out of the engine library, and asking CMake for any backend other than OpenGL stops with "not implemented". The Vulkan renderer I did finish is in raven-engine.

##Build

Everything is vendored under engine/thirdparty/ and built from source, so the first build takes a while. The script needs CMake and Ninja, and uses mold or lld when it finds them.

./compile.sh            # debug build + run
./compile.sh --release  # release build + run
./compile.sh --vulkan   # build and run the Vulkan preview instead

The binary lands in bin/<type>/monad-engine. Shaders load from assets/ relative to the working directory, which is why the script changes to the repo root first.

API docs come from Doxygen, and a GitHub Actions workflow publishes them to GitHub Pages on every push to master:

cmake --build bin/debug --target engine-docs