FlameSim — CPU-based Eulerian Fluid Solver 1.0 2D Tools 4.5 Community

Submitted by user software.twins; MIT; 2026-09-14

FlameSim is a real-time, CPU-based Eulerian fluid solver implemented as a GDExtension for the Godot Engine. Written in C++23, it provides a robust mathematical core for simulating incompressible continuous media directly on the CPU. By utilizing a fractional step (projection) method on a Staggered Grid (MAC), the library guarantees mass conservation and completely eliminates "checkerboard pressure" artifacts. This approach makes it a potential candidate for real-time applications, such as embedded systems.

**Key Features:**
- **CPU-Driven Core:** The simulation core is independent of Godot and can be connected to any other C++ project or embedded platform.
- **Dynamic Obstacles:** Applies Dirichlet boundary conditions (No-Slip condition) to the cell. Obstacles can be placed and removed "on the fly" without recalculating the entire grid.
- **Flow Visualization:** Injects a local concentration of a passive scalar (smoke, dye, flame marker) into the grid cell. The density field is transported by the calculated fluid velocity field.
- **Interactive Demo:** The Control Panel contains two sliders linked to flame intensity and wind strength, and switches that enable and disable two obstacles on the fly.

**Important Tips:**
- **Grid Optimization:** Keep the grid small (tens, not hundreds of cells per axis) and use the node's scale to stretch a small grid over the entire screen.
- **CFL Condition:** At too high flow velocities, a violation of the CFL condition is possible, leading to numerical instability. Balance the cell size, the time step, and the power of external forces.
- **Self-Managing:** The density/smoke gradually fades over time by itself — there is no need to manually extinguish it.

**Full Documentation:**
Godot Integration is distributed under the MIT License. For the complete list of methods and setup instructions, please read the full README.md in the GitHub repository.