Smoke Sim

A real-time 2D Eulerian fluid simulation built from scratch in C++/OpenGL, implemented the incompressible Navier-Stokes equations on a grid. runs on CUDA .

DEMO

Screen.Recording.2026-04-09.194138.mp4

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Features

• Incompressible Euler fluid — divergence-free velocity field via Gauss-Seidel pressure projection
• Semi-Lagrangian advection — unconditionally stable velocity and density advection
• Vorticity confinement — restores small-scale swirl lost to numerical dissipation
• Implicit diffusion — stable density diffusion via iterative solve
• Buoyancy — density-driven upward force for natural smoke rise
• Interactive mouse input — inject smoke and stir velocity with right/left mouse buttons
• Adjustable brush radius — scroll wheel to resize brush
• ImGui panel — live tuning of all simulation parameters at runtime
• Window resize support — grid recomputes on resize, no crashes
• Divergence error display — real-time incompressibility metric for debugging

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Physics

The simulation solves the incompressible Navier-Stokes equations on a 2D Eulerian grid each timestep at a fixed 120Hz:

1. Apply forces       (buoyancy, mouse injection)
2. Advect velocity    (semi-Lagrangian, self-advection)
3. Compute divergence
4. Solve pressure     (Gauss-Seidel with SOR)
5. Project velocity   (subtract pressure gradient → divergence-free)
6. Vorticity confinement
7. Advect density
8. Diffuse density    (implicit Gauss-Seidel)
9. Dissipate density  (exponential decay)
10. Damp velocity

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Dependencies

Library	Purpose
OpenGL 3.3	Rendering
GLFW	Window and input
GLAD	OpenGL loader
ImGui	Runtime UI
CUDA	GPU acceleration

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Building

Requires MSVC or GCC with C++17, OpenGL 3.3 capable GPU.

# Clone
git clone https://github.com/NobodyBuilds/smoke_sim
cd smoke_sim

# Build with your preferred system (CMake/Makefile/VS project)

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Controls

Input	Action
Right Mouse	Inject smoke + velocity
Left Mouse	Stir velocity only
Scroll Wheel	Resize brush
K	Reset simulation
Escape	Quit

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Tunable Parameters (ImGui)

Parameter	Description
tilesize	Grid cell size in pixels — smaller = higher resolution
viscosity	Density diffusion rate
dissipation	How fast smoke fades
buoyancy	Upward force strength
vorticity	Vortex confinement intensity
velDamping	Velocity decay rate
SOR	Pressure solver relaxation factor
iterations	Pressure solve iterations — higher = more accurate

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Architecture

Source.cpp       — main loop, input, sim orchestration
shader.h         — inline GLSL vertex + fragment shaders
cuda.h / .cu     — CUDA stubs 
param.h          — settings struct shared across files
ui.h             — ImGui panel

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About

Built from scratch without game engines or pre-built solvers. Math-first, correctness before performance. CUDA port in progress — the goal is to scale to high-resolution grids at real-time framerates on consumer hardware.

GitHub: NobodyBuilds