ysim

A macOS physics simulation engine for cloth dynamics and rigid bodies with GPU-accelerated collision detection.

Demo

Scene #1 — cloth draping in real time, driven by the GPU sim.

Highlights

• Dual-GPU strategy — OpenGL for rendering, Metal compute for simulation.
• GPU collision pipeline — broad phase (LBVH / Morton codes) → narrow phase (point–triangle) → constraint response, all on Metal.
• Cloth models — TriangularCloth and FastGridCloth, plus Rigid bodies, each with its own parameter set and sim path.
• Backend-parameterized core — types are templated on backend (CPU / CUDA / METAL): MeshState<BE,PR>, Scene<BE,PR>, VectorBase<BE,PR>.
• Built-in profiling — FrameProfiler tracks named timing sections with CSV export to profiles/.

Build

cmake -B build
cmake --build build
./build/ysim          # runnable from any cwd (paths resolve via exe dir + project root)

Requires: CMake 3.10+, C++17, Eigen 5.0+, GLFW 3.4, GLEW, OpenGL, Metal (macOS), Xcode CLI tools (for xcrun metal shader compilation).

Metal shaders build as part of the CMake run: .metal → .air (per file via xcrun metal -c) → default.metallib (via xcrun metallib).

Architecture

• src/main.cpp — simulation setup, main loop, and GUI (ImGui, OpenGL backend).
• src/metal/ — compute shaders carrying the bulk of the sim:
  • physics.metal — spring forces, cloth grid physics.
  • bvh.metal — BVH build, Morton codes, broad-phase collision.
  • bruteforce.metal — point–triangle narrow-phase collision.
  • spatialhashing.metal / mlspatialhashing.metal — spatial-hash broad-phase variants.
• arch-test/, arch-test-handmade/ — greenfield re-architecture experiments (virtual-interface and C++20-concepts designs); the live engine in src/ is untouched by them.

Layout

src/        engine + Metal shaders
assets/     meshes (Human.obj, teapot.obj, …)
scenes/     scene definitions
profiles/   profiler CSV output
docs/       design notes