Controls:
- Drag mouse: rotate camera
- Mouse wheel: zoom camera
- 1 through 4: different initial configurations
- U: push all particles in a random direction
- P: pause simulation
- K: kill the velocity of all particles
- E: explode the simulation
This project implements a fluid simulation using lots of tiny spherical particles and a method called Smoothed Particle Hydrodynamics. It uses the simple O(n^2) algorithm that computes the force on each particle due to all other particles. However, the GPU can still simulate over 16,000 particles at real-time framerates.
This was implemented using OpenGL 4 with Verlet integration. Under Verlet integration, the next position of the particle is calculated using only the previous two positions and the acceleration: next = 2 * current - previous + acceleration. I stored this information for all 16,384 particles in three 128x128 textures (for the previous, current, and next positions).
The simulation was implemented using Lagrangian Fluid Dynamics Using Smoothed Particle Hydrodynamics as a reference. Although the computations technically require a per-particle mass density to be computed as a separate pass before computing particle forces, re-using the mass density from the previous frame gave a noticable speedup and didn't have a visible effect on the simulation. The mass density is stored in the w-component of the position to avoid extra texture fetches in the update step.
Particles are constrained to an inside-out cube and bounce off the sides with an elasticity of 0.5. I also added two additional volume types: upright cylinder and axis-aligned box.
The particles were rendered using point primitives with a size inversely proportional to the distance from the camera. Points were rendered as spheres using the distance from the center of the point to gl_FragCoord. A per-pixel normal in world-space was reconstructed and used for top-down diffuse lighting. Screen-Space Ambient Occlusion (SSAO) was added as a second pass using the reconstructed eye-space normal.