Particle-Based-Fluid-Simulation

A 2D fluid simulation engine built from scratch with C++ and OpenGL 4.3+, heavily inspired by Sebastian Lague's "Coding Adventure: Fluid Simulation" series. By moving the heavy physics tracking onto parallel GLSL compute shaders and optimizing memory management on the CPU.

Recent Updates & Optimizations

• Robust Rigid Body Physics: Block-to-block collisions now feature complete 2D rigid body impulse resolution. Dynamic blocks correctly calculate torque and angular velocity when resting on static geometry (e.g., placing a plank on an anchor).
• Cross-Platform Build System: The CMakeLists.txt has been entirely rewritten to support out-of-the-box building on Windows, macOS, and Linux, cleanly falling back between bundled dependencies and standard OS package managers (Homebrew/pkg-config).
• Simulation Stability (Bug Fixes): Fixed severe "black hole" NaNs caused by the creation of zero-size geometries. Block structures are now mathematically protected from producing 0-area moments of inertia.
• CPU Abstraction & Memory Caching: The physics orchestration pipeline in FluidSimulation has been heavily refactored into clean, abstract stages (UpdateBlocks, HandleBlockCollisions, DispatchComputeShaders). Furthermore, CPU-side buffers utilized for Spatial Hashing counting sort are now pre-allocated dynamically, completely stripping out expensive per-frame heap allocations.

Features

Key Features:

• 8-Pass GPU Architecture: Decoupled parallel compute kernels managing position prediction, spatial hash grid generation, physical index array shuffling, density calculations, SPH pressure derivatives, viscosity, and position integration.
• Linear-Time Counting Sort (O(N)): Bypasses traditional O(N log N) sorting bottlenecks by implementing a highly efficient counting sort on the CPU, heavily optimized with pre-allocated buffer caching.
• Hardware-Instanced Rendering: Feeds particle coordinate buffers directly into the vertex fetching pipeline. The complete simulation mass is rendered using a single glDrawElementsInstanced pass.
• Numerical Sub-Stepping: Divides each frame's update into multiple high-frequency micro-steps to withstand the immense hydrostatic pressure of dense fluid columns.
• Dynamic Color Grading: A color palette computed completely on the GPU inside the vertex shader, dynamically blending particle colors based on real-time velocity lengths.

Controls & Interaction

Input	Mode
Spacebar	Pause/Resume Simulation
Mouse Scroll	Adjust Brush Size
F1	Open Config Prompt
Key "1"	Switch to Force Field Mode: • Left Click: Attract Fluid Mass • Right Click: Repel Fluid Mass
Key "2"	Switch to Anchor Geometry Mode: • Left Click & Drag: Deploy Static Anchor Block • Right Click: Delete Block Under Cursor
Key "3"	Switch to Moveable Geometry Mode: • Left Click & Drag: Deploy Dynamic Rigid Body Block • Right Click: Delete Block Under Cursor

Requirements

• C++17 Compiler or higher
• CMake 3.16+
• OpenGL 4.3+ Capable Hardware Driver (Required for Compute Shaders and std430 SSBO Layouts)
• Dependencies: Uses bundled GLM, GLEW, and GLFW on Windows, and dynamically links against system OS libraries natively on macOS and Linux.

Build & Run

On Linux / macOS

cmake -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build
./build/FluidSimulation

On Windows

cmake -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build
build\Release\FluidSimulation.exe