A work in progress game engine.

Demos

See the executables from ghegin-games.cabal in the examples/ directory. The few work in progress/unpolished executables are:

• ocean-waves
• planets-core
• domain-warping
• fir-juliaset, a port of FIR's juliaset to ghengin.
• mandlebrot-set

Ocean waves

Based on https://dl.acm.org/doi/abs/10.1145/15922.15894

Unique? features:

• Shader first -- the engine is design with custom shaders in the center, and a lot of compile time validation and runtime data is based on the shader
• Compile time validation of compatibility between the game defined materials, meshes and the game defined shader programs.
• It's written in Haskell
• ...

Key ideas

I haven't had much time to write about this (even more so with the big linear-types refactor on the way), but the key ideas are:

• RenderPackets are things that get rendered, and each render packet is defined by:

  • A Mesh
  • a Material
  • and a RenderPipeline

• Meshes are vertices together with properties to influence the render of these vertices, and are parametrized by:

  • A type list describing the properties of each vertex in this mesh
  • (This is not yet implemented:) A type list describing the property bindings that describe this mesh and get bound to descriptor set #2 for each different mesh that is drawn.
    • Note that multiple render packets sharing the same mesh can be drawn while the mesh properties being still only bound once.

• Materials are group of properties that influence how all render packets sharing this Material are rendered; it is parametrized by:

  • A type list with the type of each property describing this material, which will get bound once to descriptor set #1 for every different material.
    • Note that multiple render packets with different meshes may share the same material, and the material properties will be shared across mesh draws without being rewritten
      • (Each material may get bound more than once, if there's no clear serialization of draw calls that ensures the material only needs to be bound once -- this has to due with heuristics in the render queue, I don't recall all the details)

• Render pipelines are group of properties and descriptions of render pipelines in graphics parlor, that define how all render packets that share this render pipeline are rendered (across different materials and meshes); it is parametrized by:

  • A type list describing the properties shared accross all render packets drawn with this render pipeline, that will be bound in descriptor set #0
  • A type-level complete description of the shader, which is the type of the shader program in the FIR shader language.

• The Compatible constraint must be satisfied in order to construct a render packet. This constraint validates, at compile time, that:

  • For the Mesh (see also CompatibleMesh)
    • The properties of each vertex match the vertice properties expected by the shader
    • (This is not yet implemented:) The mesh properties match the properties expected to be bound at descriptor set #2 in the shader
  • For the Material (see also CompatibleMaterial)
    • The properties of the material match the properties expected to be bound at descriptor set #1 by the shader
  • For the RenderPipeline (see also CompatiblePipeline)
    • The properties of the pipeline match the properties expected to be bound at descriptor set #0 by the shader

• ...

• The Core of the engine is abstract over the renderer implementation (through backpack), though we only have a vulkan implementation of the renderer, and the Core isn't yet fully standalone

• The Core of the engine is much like the Core in GHC: it strives to be a tiny but very expressive engine, that can represent in its completeness the full engine (which provides additional features not directly available in Core, but that can be expressed in it), for example:

  • The Camera construct is not part of Core, for it can be fully defined as a RenderPipeline property that gets bound in descriptor set #0 once per render pipeline, and some shader math. Of course, this ought to be provided as a plug and play capability in the full engine (say, one just has to import the Camera module, add it as a property of the render pipeline, and call the imported camera shader function in their own shader)
    • It's prettty good how in the shaders being written in Haskell one can easily use other engine-defined shader functions
  • ...

Where's the action at?

The current demo is planets. To run it call:

cabal run planets

I'm trying to write a set of tutorials in some sort of book, based on an ocean simulation, though progress has been slow as I've been busy with the linear types refactor.

Write ups:

• https://discourse.haskell.org/t/monthly-update-on-a-haskell-game-engine/5515

Notes

Module dependencies:

find src/ ghengin-core/ ghengin-core-indep/ ghengin-vulkan/ -name '*.hs' | xargs graphmod -q -p | dot -T svg -o mods.svg

General dependencies:

cabal build -j --ghc-options=-fwrite-ide-info
calligraphy Ghengin.Core.* --exports-only --collapse-data --collapse-classes --output-stdout | dot -T svg -o img.svg -Kfdp

Debugging segfaults:

Compile with ghc-options: -rtsopts and use +RTS -C0 to disable timer clock something garbage collection (look the flag up). Also, use flag +dev when developing

# try
$(cabal list-bin planets) +RTS -C0
# also, if planets is compiled with -g
lldb -- $(cabal list-bin planets) +RTS -C0

More resources:

• https://developer.nvidia.com/blog/vulkan-dos-donts/
• https://zeux.io/2020/02/27/writing-an-efficient-vulkan-renderer/
• https://www.intel.com/content/www/us/en/developer/articles/training/api-without-secrets-introduction-to-vulkan-part-6.html
• https://arm-software.github.io/vulkan_best_practice_for_mobile_developers/samples/performance/descriptor_management/descriptor_management_tutorial.html
• Creating the Art of ABZU

WIP: Packaging

Need to work out a packaging library. Notes:

• Vulkan dynamic library could be included in the bundle if the executable link path is changed (see otool -L and install_name_tool)
• File system resources must be accessed through some hoops or it all goes to shit. It would be good to wrap this in a library which uses CPP to determine whether to use MacOS's CoreFoundation things, or Android's bundles, or just directly gets the resource

On MacOS:

App bundle structure: https://www.lunarg.com/wp-content/uploads/2022/05/The-State-of-Vulkan-on-Apple-15APR2022.pdf

Vulkan dynamically linked libraries should be included in the bundle, use install_name_tool to set location?

Have spent quite some time but haven't got the .app to open yet, despite the executable working otherwise...

Clues:

• Ghengin game doesn't work
• Simple gloss app manually bundled works
• SDL Vulkan Triangle manually bundled also works, despite the otool -L showing @rpath/libvulkan.1.dylib
• GLFW-b OpenGL demo manually bundled works trivially
• FIR SDL Vulkan demo trivially works too
• GLFW + vulkan example in glfw source github repository also works trivially
• SDL + vulkan + dear-imgui.hs example fails to open!!
• GLFW + OpenGL + dear-imgui.hs example works trivially

Current conclusion: Vulkan + Dear-ImGui.hs combination has something that makes it fail to open when bundled in a .app

However, building the vulkan + glfw + dear-imgui example from the original C++ source succeeds. So, is the error in the haskell dear-imgui + vulkan ?

Turns out the vulkan + dear-imgui doesn't work because of an asset it depends on, but if I hardcode the path then it works.

So, my engine's apps are the only ones not working with RBSStateCapture remove item called for untracked item

Fixed: after narrowing down the commit in which my app became unrunnable, I realized the output logging file was causing the silent crash-on-start. What a truly awful, painful experience.

Note on resources

The assets folder is copied to the bundle, so all resources should be in assets

ghengin-core

What ghengin-core does and does not:

• Does not implement a game-loop, nor a time step strategy
• Does not implement a scene-graph
• Nor (game) object positioning in terms of so-called "world coordinates"
• Does not provide a camera
• Does not manage game objects/entities in any way (no ECS, no FRP, actually, no concept of game object whatsover)
• Does not have a UI abstraction, but will allow renderpasses to be managed in such a way that one can add outside of Core, e.g., a dear-imgui render pass
• Has an (editable) Render Queue with the render packets (meshes + properties + material properties + pipeline with shader) that are rendered every frame
• Can express all of the above things it "does not" do with the existing concepts and combinators
• Handles double-buffering (eventually configurable?) semantics for the 'render' function, i.e. blocks after drawing a second frame
  • Actually, it's the renderer implementation that handles this

Add-ons

These add-ons exist as separate packages, and are all included in ghengin, the batteries included engine. These also attempt to be somewhat independent from ghengin-core when possible.

• ghengin-scene-graph, which defines a scene-graph and world coordinate space with objects related in a hieararchy with properties defined relative to their parents (i.e. a scene, in its usual meaning)
• ghengin-camera, a camera object, shader, and update function (i.e. a camera, in its usual meaning)
• ghengin-models, to load and render 3D models
• ghengin-lighting, that provides lighting functions/models like the Blinn-Phong model
• ghengin-dearimgui, for UIs based on ghengin

Ghengin

ghengin provides game-development abstractions on top of ghengin-core, and is more developer friendly in the sense that it does not require linear types

Other design ideas

• The render/draw function takes an action which "draws" things, which, depending on the implementation, either batches the drawcall or actually makes the draw call.