What it is
psiEngine is a small engine for looking at physics I compute on the GPU. Vulkan does the rendering, the GPU does the compute, and a node graph sits in the middle so I can wire a simulation up without recompiling every time I want to change a constant.
It is not a game engine and I have no plans to make it one. It exists because every time I write a kernel that produces a cloud of numbers I want to see the cloud, rotate it, poke at the parameters and watch it change, and I got tired of doing that through matplotlib and a screenshot. The first real workload is the hydrogen atom: give it (n, l, m) and it draws the orbital.
Source: github.com/nnamu-cl/psiEngine
How it is put together
Rendering is Vulkan. SDL3 owns the window and input, volk loads the API, and shaders are written in Slang and compiled at runtime, so a shader edit is a restart and not a rebuild. The main scene layer is GPU driven: a compute pass builds the indirect draw commands, and the vertex work for lines, circles and orbital samples happens in compute shaders before anything reaches the graphics pipeline.
Compute runs on the GPU too. Inside the engine that is Vulkan compute. The heavy numerical work, sampling electron densities at the bandwidth roof, is CUDA and lives in its own repo, cuda-orbital-sampler, where I can profile it properly. The engine is the place those samples get drawn.
Everything in the scene is a component. A tiny ECS (component store, type ids) and a set of components: Transform, MeshRenderer, LineRenderer, VolumeRenderer, Atom (the quantum numbers, validated so l < n and |m| <= l) and AtomVisualizer (how those numbers become geometry). Components draw their own inspector UI.
The node graph drives values. A typed node system (float, int, vec2 to vec4, mat4) with value, math, vector, object and graph nodes, drawn on top of imgui_node_editor. Node outputs bind to component properties, so a sine node wired into a transform is an animation, and a constant node wired into an atom is a slider that changes the orbital.
Projects save and load. A project registry, window state and scene serialisation through glaze JSON.
Two applications sit on top. The psi app is the one I actually use, with a world viewport for placing and manipulating objects with gizmos and a graph editor for wiring the node graph. A second app, decisions, is a side experiment: a cashflow scenario engine scripted in Lua through sol2. It shares the window library and nothing else.
Stack
C++23, CMake, Vulkan, SDL3, Slang, Dear ImGui, imgui_node_editor, ImGuizmo, im3d, ImPlot, GLM, glaze, KTX, sol2 and Lua. Developed on Linux with Wayland; a Windows path exists but has not been built in a while.
Status
Work in progress and it moves in bursts. The rendering path, node graph, saving and the atom components work. What I am building towards is the CUDA sampler feeding the visualizer directly rather than through dumps, and a proper simulation loop on the world layer.
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