Working with fluid simulation in Unity often becomes a technical challenge, especially when you want water, lava, erosion, and terrain interaction to behave consistently in real time. Heightmap-based systems can get you part of the way there, but getting something interactive, performant, and visually coherent usually requires a specialized tool.
Fluid Frenzy by Frenzy Byte, is a GPU-accelerated fluid simulation and renderer created to bring physically motivated 2.5D fluid behavior into Unity projects while supporting terrain interaction, terraforming, and multi-fluid mixing.
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What Is Fluid Frenzy and How It Works
According to Frenzy Byte, Fluid Frenzy is a GPU-accelerated 2.5D fluid simulation system built on shallow water equations. It allows fluids such as water and lava to flow across Unity Terrain, custom terrain systems, or any heightmap texture. The simulation adapts to terrain height, obstacles, and modifiers that add or remove fluid, apply forces, or generate waves.
Fluid Frenzy uses GPU-based solvers to update height, depth, and velocity fields in real time. Optional GPU particles can appear during conditions such as breaking waves or waterfalls, and the GPU-driven quadtree LOD system increases detail near the viewer while remaining efficient at larger scales. Two fluid layers can exist in the same simulation, enabling fluid mixing behaviors like water interacting with lava to form rock.
Terrain terraforming is supported through a custom system that allows the simulation to modify height and splat maps at runtime. Rigidbodies can receive buoyancy and advection forces based on local fluid motion. Developers can sample simulation data in C# through the FluidSimulationManager to retrieve height, depth, velocity, or layer information, and use event triggers when fluid enters or leaves a position.
Samples, shaders, and interaction components are distributed through Unity’s Package Manager using the Hybrid Package workflow.
Samples, shaders, and interaction components are distributed through Unity’s Package Manager using the Hybrid Package workflow.
Main Features
- 2.5D Shallow Water Simulation: Fluid Frenzy uses shallow water equations to simulate wave behavior, flow, and height-based movement across a surface.
- Terrain Interaction: The simulation adapts to Unity Terrain, the custom Terraform Terrain system, or any other heightmap-based terrain. Fluids follow slopes, fill depressions, and move around obstacles.
- Terraforming: The system includes real-time terrain modification, allowing fluids to erode and alter terrain layers. This can be used to create dynamic environments or god-game mechanics.
- Fluid Layer Mixing: Two fluid layers can interact and mix. Water and lava, for example, can combine to form rock on the terrain.
- GPU-Accelerated Rendering: A GPU-driven quadtree LOD system improves performance by focusing higher detail near the viewer while reducing cost elsewhere.
- GPU Particles: Optional GPU-accelerated particles can appear during events like breaking waves or waterfalls, interacting with the simulation.
- Obstacle Interaction: Objects in the scene can be marked as obstacles so fluids flow around or collide with them.
- Interaction Components: Modifiers can add or remove fluid, apply forces, or generate waves directly in the simulation.
- Water and Lava Rendering - Built-in shaders include features such as:
- Reflection
- Reflection
- Subsurface scattering
- Foam mapping
- Vertex displacement
- Emission and velocity-based heat (lava)
- C# Scripting Access: Developers can query fluid height, depth, velocity, and layers using the FluidSimulationManager and event triggers.
Use Cases
Fluid Frenzy can be used for:
- Dynamic rivers flowing over terrain.
- Lava systems with thermal behavior.
- Erosion-based environments and god-game mechanics.
- Water simulations for gameplay interaction.
- Prototyping terrain alteration systems.
- Stylized or realistic liquid rendering.
- Scenes that require runtime buoyancy or fluid-driven physics.
🎥 Here is a quick look at the Forest demo, shared by the author:
Limitations
According to the developer:
- This is a 2.5D shallow water equation simulation, meaning fluids can only flow over objects, not under them.
- Simulation speed has a maximum limit due to pixel-based movement.
- Multiplayer is not supported because network synchronization of fluid data is impractical.
- Best performance is achieved with Shader Model 5.0 on DirectX or Vulkan.
- WebGL 2 support is in beta and does not include GPU particles or steam.
Similar and Useful Tools
- FluXY – 2.5D fluid simulator: FluXY is a 2.5D fluid simulator for Unity that lets you create fluid dynamics (liquids flowing, interacting) in a more physics-oriented setup. It supports flowing liquids in a pseudo-3D environment (2.5D) with user interaction.
Differences: Compared to Fluid Frenzy, FluXY is more narrowly focused on fluid motion rather than full terrain erosion, lava + water mixing, or high-end GPU LOD terrain interactions. If your task is purely fluid flow rather than large terrain/erosion systems, FluXY might suffice.
- Cocuy: The Fluid Simulator: Cocuy offers fluid simulation via particles and shaders for stylized water/fluids in Unity, targeting VFX rather than full physics simulation.
Differences: While Fluid Frenzy aims at realistic terrain-flow, buoyancy, and GPU acceleration, Cocuy is more VFX / visual effect oriented (stylized fluids, particle-based) and likely lighter weight. Good for visual flair but less heavy simulator.
- Lightweight Fluids: A low-cost fluid simulation tool for Unity that offers simple fluid behaviors, ideal for smaller projects or less demanding fluid effects.
Differences: Compared to Fluid Frenzy’s full feature set (terrain interaction, GPU LOD, lava+water mixing), Lightweight Fluids is far simpler and less feature-rich—better for prototyping or simpler needs, not full scale fluid simulation.
✨ Fluid Frenzy is now available on the Unity Asset Store.
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