Making fire feel alive: Real-time fluid simulation in Ignitement

Solo developer Sørb details the real-time 2D fluid simulation powering fire and lava VFX in the upcoming action roguelite Ignitement, built entirely in Unity. The system runs via Graphics.Blit on a small set of textures (density, velocity, temperature, reaction) using fragment shaders instead of compute shaders for broad hardware compatibility. Fire rendering uses a parallax trick for pseudo-3D depth, embers are GPU-driven particles sampling the velocity field, and a downsampled reaction texture doubles as a dynamic light map affecting environment shaders and UI. Crucially, the reaction texture is read back to the CPU each frame via AsyncGPUReadback to drive gameplay damage logic, making fire a true gameplay mechanic. Key trade-offs include a 2D-only simulation and a camera-following domain to keep costs low while maintaining the illusion of a continuous world.