fluid.cpp

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/// @file fluid.cpp
/// @brief Single-switch dispatch from Backend enum to SPH backend implementations.
///
/// Mirrors src/backends/dispatch.cpp exactly:
///   - Includes both seq and omp impl.hpp headers
///   - switch(params_.policy) routes each phase to the correct backend
///   - Non-computational methods (add_particle, clear, ...) live here directly
///
/// Adding a new backend:
///   1. Add the enumerator to num::Backend in include/core/policy.hpp
///   2. Create apps/fluid_sim/backends/<name>/ with impl.hpp + fluid.cpp + heat.cpp
///   3. Add `case num::Backend::<name>:` to the switch in step()
///   4. Register the .cpp files in apps/fluid_sim/CMakeLists.txt
 
#include "fluid.hpp"
#include "backends/seq/impl.hpp"
#include "backends/omp/impl.hpp"
 
namespace physics {
 
FluidSolver::FluidSolver(const FluidParams& params)
    : params_(params)
    , grid_(2.0f * params.h,
            params.xmin, params.xmax,
            params.ymin, params.ymax)
{}
 
void FluidSolver::add_particle(float x, float y, float vx, float vy, float temperature) {
    Particle p{};
    p.x = x;  p.y = y;
    p.vx = vx; p.vy = vy;
    p.evx = vx; p.evy = vy;
    p.density     = params_.rho0;
    p.pressure    = 0.0f;
    p.temperature = temperature;
    particles_.push_back(p);
}
 
void FluidSolver::add_body(const RigidBody& body) { bodies_.push_back(body); }
void FluidSolver::clear() { particles_.clear(); bodies_.clear(); }
 
// --- Main step  -- policy dispatch ---------------------------------------------
 
void FluidSolver::step() {
    if (particles_.empty()) return;
 
    for (Particle& p : particles_) { p.ax = p.ay = 0.0f; p.dT_dt = 0.0f; }
 
    grid_.build(particles_);   // O(n + C) counting sort  -- always sequential
 
    const HeatParams hp{params_.h, params_.alpha_T, params_.h_conv, params_.mass};
 
    switch (params_.policy) {
 
    case num::Backend::omp:
        backends::omp::compute_density_pressure(particles_, params_, grid_);
        backends::omp::compute_forces(particles_, params_, grid_);
        backends::omp::heat_compute(particles_, bodies_, grid_, hp);
        backends::omp::body_collisions(particles_, bodies_, params_);
        backends::omp::integrate(particles_, params_);
        backends::omp::enforce_boundaries(particles_, params_);
        backends::omp::update_temp_range(particles_, bodies_, T_min_, T_max_);
        backends::seq::integrate_bodies(bodies_, params_);  // M bodies tiny  -- seq
        break;
 
    default:  // seq: Newton pair traversal
        backends::seq::compute_density_pressure(particles_, params_, grid_);
        backends::seq::compute_forces(particles_, params_, grid_);
        backends::seq::heat_compute(particles_, bodies_, grid_, hp);
        backends::seq::body_collisions(particles_, bodies_, params_);
        backends::seq::integrate(particles_, params_);
        backends::seq::enforce_boundaries(particles_, params_);
        backends::seq::update_temp_range(particles_, bodies_, T_min_, T_max_);
        backends::seq::integrate_bodies(bodies_, params_);
        break;
    }
}
 
} // namespace physics