Verlet-based Particle Simulator

2D particle simulation using C++ with SFML rendering. Designed as a concurrency/performance showcase: stable physics via Verlet integration, broad-phase acceleration via spatial hashing, and a multithreaded collision solver implemented with a persistent worker pool and slice scheduling.

This work was inspired by the work of Keyframe Codes & John Buffer (Pezzza's Work) but built irrespective of their implementation. Respective GitHub repos: Keyframe, Pezzza.

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Particle simulator demonstation.

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Key Features

• Verlet Integration (stability at scale)
  Started with Euler-style integration but encountered jitter/instability and energy gain in dense, highly constrained scenes. Switched to Verlet integration (position + previous position), improving stability for higher particle counts and frequent collision constraints.

• Spatial Hashing Grid (broad-phase collision acceleration)
  Particles are inserted into a uniform grid cell based on position. Collision checks are limited to the current cell and a small neighborhood, reducing the naive all-pairs cost from O(n²) to near O(n) in typical distributions (bounded local density).

• Multithreaded Collision Solver (core performance work)
  Profiling showed collision resolution dominated the update loop. The solver was parallelized using:

  • a flat, fixed-capacity grid (reduces allocations and improves locality)
  • column-major layout to make column ranges contiguous in memory
  • vertical slicing so each worker processes independent column ranges
  • an even/odd two-pass schedule to avoid adjacent-slice contention during neighbor checks
  • a persistent worker pool (condition variables + atomic job index) to avoid per-frame thread overhead

• Deterministic Image Colouring Mode (optional)
  If assets/image.(png|jpg|jpeg|bmp|tga) exists, it is resized to the window dimensions and sampled to assign colours deterministically by particle index. This enables “image reconstruction” effects when particles converge to a predetermined final configuration.

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Build & Run

Dependencies

• SFML 2.5
• C++ (17 or later)
• CMake

Build

From project root:

mkdir build
cd build
cmake ..
cmake --build . -j

Run

From build directory

./particle-sim

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Controls

• Mouse (hold left): attract/accelerate nearby particles
• Arrow keys: change gravity direction
• Esc: exit