SPlisHSPlasH

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SPlisHSPlasH is an open-source library for the physically-based simulation of fluids using the...
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### Minimal working example with GUI

Source: https://splishsplash.readthedocs.io/en/latest/py_getting_started.html

Minimal Python script to run a simulation with a GUI. Requires SPlisHSPlasH installed correctly and scene files in the data directory.

```python
import pysplishsplash as sph

def main():
    base = sph.Exec.SimulatorBase()
    base.init()
    gui = sph.GUI.Simulator_GUI_imgui(base)
    base.setGui(gui)
    base.run()

if __name__ == "__main__":
    main()
```

--------------------------------

### FoamGenerator example command

Source: https://splishsplash.readthedocs.io/en/latest/FoamGenerator.html

Example command to run FoamGenerator with specified start/end frames, radius, foam scale, input and output files.

```bash
FoamGenerator -s 1 -e 500 -r 0.025 --foamscale 1000 -i output\DamBreakModelDragons\partio\ParticleData_Fluid_#.bgeo -o output\DamBreakModelDragons\foam\foam_#.bgeo
```

--------------------------------

### Build and install wheel for development

Source: https://splishsplash.readthedocs.io/en/latest/py_getting_started.html

Builds a Python wheel and installs it with pip. Run these commands again to update the installation after rebuilding.

```bash
cd SPlisHSPlasH
python setup.py bdist_wheel
pip install -I build/dist/*.whl
```

--------------------------------

### Install Python bindings via setup.py

Source: https://splishsplash.readthedocs.io/en/latest/build_from_source.html

Builds a wheel and installs it. Run from project root. Recommended to use a virtual environment. Additional CMake variables can be appended after bdist_wheel.

```bash
git clone https://github.com/InteractiveComputerGraphics/SPlisHSPlasH.git
cd SPlisHSPlasH
python setup.py bdist_wheel
pip install build/dist/*.whl
```

--------------------------------

### MeshSkinning command line example

Source: https://splishsplash.readthedocs.io/en/latest/MeshSkinning.html

Example command to run MeshSkinning with a scene file, enabling splitting and overwrite options. The scene file path is provided as an argument.

```bash
MeshSkinning --splitting --overwrite --scene ..\data\Scenes\Beam.json
```

--------------------------------

### VolumeSampling.exe example command

Source: https://splishsplash.readthedocs.io/en/latest/VolumeSampling.html

Example command to run the VolumeSampling tool with mode 4 (Kugelstadt et al. 2021), input bunny.obj, and output bunny.vtk.

```bash
VolumeSampling.exe --mode 4 -i ..\data\models\bunny.obj -o bunny.vtk
```

--------------------------------

### Install Python bindings directly from git

Source: https://splishsplash.readthedocs.io/en/latest/build_from_source.html

Combines all installation steps into one command. Loses incremental rebuild capability; rebuilding requires full project rebuild.

```bash
pip install git+https://github.com/InteractiveComputerGraphics/SPlisHSPlasH.git
```

--------------------------------

### Build and install Python bindings from source

Source: https://splishsplash.readthedocs.io/en/latest/build_from_source.html

Builds a wheel and installs the Python bindings. Run from the project root. Optionally append additional CMake variables after 'bdist_wheel'.

```bash
git clone https://github.com/InteractiveComputerGraphics/SPlisHSPlasH.git
cd SPlisHSPlasH
python setup.py bdist_wheel
pip install build/dist/pySPlisHSPlasH-2.8.3-cp37-cp37m-win_amd64.whl
```

--------------------------------

### Run SPHSimulator with a scene file

Source: https://splishsplash.readthedocs.io/en/latest/build_from_source.html

Starts the simulator from the command line with a specified scene file. The scene is loaded and the simulation starts when pause mode is disabled.

```bash
./SPHSimulator ../data/Scenes/DoubleDamBreak.json
```

--------------------------------

### Configuration block example

Source: https://splishsplash.readthedocs.io/en/latest/file_format.html

Example JSON configuration block for a SPlisHSPlasH scene file, showing general simulation settings and pressure solver parameters (WCSPH, PBF, DFSPH). Note: the WCSPH block is missing a comma after its closing brace in the source.

```json
"Configuration": 
{
    "pause": true,
    "sim2D": false, 
    "timeStepSize": 0.001,
    "numberOfStepsPerRenderUpdate": 2,
    "particleRadius": 0.025, 
    "simulationMethod": 4,
    "gravitation": [0.0,-9.81,0], 
    "cflMethod": 1, 
    "cflFactor": 1,
    "cflMaxTimeStepSize": 0.005,
    "WCSPH": 
    {
      "stiffness": 50000,
      "exponent": 7
    }
    "PBF": 
    {
      "minIterations": 2,
      "maxIterations": 100,
      "maxError": 0.01,
      "velocityUpdateMethod": 0
    },
    "DFSPH": 
    {
      "minIterations": 2,
      "maxIterations": 100,
      "maxError": 0.01,
      "maxIterationsV": 100,
      "maxErrorV": 0.1,		
      "enableDivergenceSolver": true
    }
}
```

--------------------------------

### Install Python bindings dependencies and pipx

Source: https://splishsplash.readthedocs.io/en/latest/build_from_source.html

Installs Python development packages and pipx for using Python bindings with -DUSE_PYTHON_BINDINGS=On. Ensures a working Python installation is in PATH.

```bash
sudo apt install python3-dev python3-pip python3-venv
python3 -m pip install pipx
python3 -m pipx ensurepath
```

--------------------------------

### Install SPlisHSPlasH with pip

Source: https://splishsplash.readthedocs.io/en/latest/py_getting_started.html

Installs the Python bindings using pip. The trailing slash is important to install from the local directory; run from one directory above the cloned source.

```bash
pip install SPlisHSPlasH/
```

--------------------------------

### Minimal working example without GUI

Source: https://splishsplash.readthedocs.io/en/latest/py_getting_started.html

Minimal Python script to run a simulation without a GUI. Uses base.init(useGui=False) and sets STOP_AT to 10.0 (float).

```python
import pysplishsplash as sph

def main():
    base = sph.Exec.SimulatorBase()
    base.init(useGui=False)
    base.setValueFloat(base.STOP_AT, 10.0) # Important to have the dot to denote a float
    base.run()

if __name__ == "__main__":
    main()
```

--------------------------------

### Material configuration example with XSPH, viscosity, and vorticity

Source: https://splishsplash.readthedocs.io/en/latest/file_format.html

Example JSON block for defining a material with id 'Fluid'. Includes density, particle coloring fields, and nested blocks for XSPH, Standard viscosity, and Bender et al. 2017 vorticity. The 'id' must match FluidBlock, FluidModel, or Emitter to apply the material.

```json
{
    "Materials": [
        {
            "id": "Fluid",
            "density0": 1000, 
            "colorField": "velocity",
            "colorMapType": 1,
            "renderMinValue": 0.0,
            "renderMaxValue": 5.0,
            "viscosityMethod": 1, 
            "vorticityMethod": 1, 
            "maxEmitterParticles": 1000,
            "emitterReuseParticles": false,
            "emitterBoxMin": [-4.0,-1.0,-4.0],
            "emitterBoxMax": [0.0,4,4.0],
            "XSPH": 
            {
              "xsph": 0.0,
              "xsphBoundary": 0.0
            },
            "Standard viscosity":
            {
              "viscosity": 0.01
            },
            "Bender et al. 2017": 
            {
              "vorticity": 0.15,
              "viscosityOmega": 0.05,
              "inertiaInverse": 0.5
            } 
        }
    ]
}
```

--------------------------------

### Viscosity_Weiler2018.cpp source code

Source: https://splishsplash.readthedocs.io/en/latest/api/program_listing_file_SPlisHSPlasH_Viscosity_Viscosity_Weiler2018.cpp.html

Full source code of Viscosity_Weiler2018.cpp as displayed in the documentation. It includes the class implementation, parameter setup, and the start of the AVX-optimized matrix-vector product.

```cpp
#include "Viscosity_Weiler2018.h"
#include "SPlisHSPlasH/TimeManager.h"
#include "Utilities/Timing.h"
#include "Utilities/Counting.h"
#include "SPlisHSPlasH/Simulation.h"
#include "SPlisHSPlasH/BoundaryModel_Akinci2012.h"
#include "SPlisHSPlasH/BoundaryModel_Koschier2017.h"
#include "SPlisHSPlasH/BoundaryModel_Bender2019.h"
#include "SPlisHSPlasH/Utilities/MathFunctions.h"

using namespace SPH;
using namespace GenParam;

std::string Viscosity_Weiler2018::METHOD_NAME = "Weiler et al. 2018";
int Viscosity_Weiler2018::VISCOSITY_COEFFICIENT = -1;
int Viscosity_Weiler2018::ITERATIONS = -1;
int Viscosity_Weiler2018::MAX_ITERATIONS = -1;
int Viscosity_Weiler2018::MAX_ERROR = -1;
int Viscosity_Weiler2018::VISCOSITY_COEFFICIENT_BOUNDARY = -1;

Viscosity_Weiler2018::Viscosity_Weiler2018(FluidModel *model) :
    NonPressureForceBase(model), m_vDiff()
{
    m_viscosity = static_cast<Real>(0.01);
    m_maxIter = 100;
    m_maxError = static_cast<Real>(0.01);
    m_iterations = 0;
    m_boundaryViscosity = 0.0;
    m_tangentialDistanceFactor = static_cast<Real>(0.5);

    m_vDiff.resize(model->numParticles(), Vector3r::Zero());

    model->addField({ "velocity difference", METHOD_NAME, FieldType::Vector3, [&](const unsigned int i) -> Real* { return &m_vDiff[i][0]; }, true });
}

Viscosity_Weiler2018::~Viscosity_Weiler2018(void)
{
    m_model->removeFieldByName("velocity difference");

    m_vDiff.clear();
}

void Viscosity_Weiler2018::initParameters()
{
    NonPressureForceBase::initParameters();

    VISCOSITY_COEFFICIENT = createNumericParameter("viscosity", "Viscosity coefficient", &m_viscosity);
    setGroup(VISCOSITY_COEFFICIENT, "Fluid Model|Viscosity");
    setDescription(VISCOSITY_COEFFICIENT, "Coefficient for the viscosity force computation");
    RealParameter* rparam = static_cast<RealParameter*>(getParameter(VISCOSITY_COEFFICIENT));
    rparam->setMinValue(0.0);

    VISCOSITY_COEFFICIENT_BOUNDARY = createNumericParameter("viscosityBoundary", "Viscosity coefficient (Boundary)", &m_boundaryViscosity);
    setGroup(VISCOSITY_COEFFICIENT_BOUNDARY, "Fluid Model|Viscosity");
    setDescription(VISCOSITY_COEFFICIENT_BOUNDARY, "Coefficient for the viscosity force computation at the boundary.");
    rparam = static_cast<RealParameter*>(getParameter(VISCOSITY_COEFFICIENT_BOUNDARY));
    rparam->setMinValue(0.0);

    ITERATIONS = createNumericParameter("viscoIterations", "Iterations", &m_iterations);
    setGroup(ITERATIONS, "Fluid Model|Viscosity");
    setDescription(ITERATIONS, "Iterations required by the viscosity solver.");
    getParameter(ITERATIONS)->setReadOnly(true);

    MAX_ITERATIONS = createNumericParameter("viscoMaxIter", "Max. iterations (visco)", &m_maxIter);
    setGroup(MAX_ITERATIONS, "Fluid Model|Viscosity");
    setDescription(MAX_ITERATIONS, "Max. iterations of the viscosity solver.");
    static_cast<NumericParameter<unsigned int>*>(getParameter(MAX_ITERATIONS))->setMinValue(1);

    MAX_ERROR = createNumericParameter("viscoMaxError", "Max. visco error", &m_maxError);
    setGroup(MAX_ERROR, "Fluid Model|Viscosity");
    setDescription(MAX_ERROR, "Max. error of the viscosity solver.");
    rparam = static_cast<RealParameter*>(getParameter(MAX_ERROR));
    rparam->setMinValue(static_cast<Real>(1e-6));
}

#ifdef USE_AVX

void Viscosity_Weiler2018::matrixVecProd(const Real* vec, Real *result, void *userData)
{
    Simulation *sim = Simulation::getCurrent();
    Viscosity_Weiler2018 *visco = (Viscosity_Weiler2018*)userData;
    FluidModel *model = visco->getModel();
    const unsigned int numParticles = model->numActiveParticles();
    const unsigned int fluidModelIndex = model->getPointSetIndex();
    const unsigned int nFluids = sim->numberOfFluidModels();
    const unsigned int nBoundaries = sim->numberOfBoundaryModels();

    const Real h = sim->getSupportRadius();
    const Real h2 = h*h;
    const Real dt = TimeManager::getCurrent()->getTimeStepSize();
    const Real density0 = model->getDensity0();
    const Real mu = visco->m_viscosity * density0;
    const Real mub = visco->m_boundaryViscosity * density0;
    const Real sphereVolume = static_cast<Real>(4.0 / 3.0 * M_PI) * h2*h;

    Real d = 10.0;
    if (sim->is2DSimulation())
        d = 8.0;

    const Scalarf8 d_mu_rho0(d * mu  * density0);
    const Scalarf8 d_mub(d * mub);
    const Scalarf8 h2_001(0.01f*h2);
    const Scalarf8 density0_avx(density0);

```

--------------------------------

### void init()

Source: https://splishsplash.readthedocs.io/en/latest/api/class_s_p_h_1_1_debug_tools.html

Initializes the DebugTools instance.

```APIDOC
## void init()

### Description
Initializes the DebugTools instance.

### Method
Member function

### Signature
`void init()`

```

--------------------------------

### FluidBlocks JSON configuration example

Source: https://splishsplash.readthedocs.io/en/latest/file_format.html

Defines an axis-aligned fluid block with denseMode, start, end, translation, and scale parameters. The denseMode values are 0 (regular), 1 (more dense), and 2 (dense).

```json
"FluidBlocks": [
    {
        "denseMode": 0,
        "start": [-2.0, 0.0, -1],
        "end": [-0.5, 1.5, 1],
        "translation": [1.0, 0.0, 0.0],
        "scale": [1, 1, 1]
    }
]	
```

--------------------------------

### Emitter::emitParticlesCircle - Circular Emission Setup

Source: https://splishsplash.readthedocs.io/en/latest/api/program_listing_file_SPlisHSPlasH_Emitter.cpp.html

Starts the circular emission function. Retrieves time, particle radius, and emission direction. Adjusts emission velocity to a cleanup value when outside the emission time window. Within the emission window, computes the animation margin and circular geometry parameters (height, radius) for particle placement.

```cpp
void Emitter::emitParticlesCircle(std::vector <unsigned int> &reusedParticles, unsigned int &indexReuse, unsigned int &numEmittedParticles)
{
    TimeManager *tm = TimeManager::getCurrent();
    const Real t = tm->getTime();
    const Real timeStepSize = tm->getTimeStepSize();
    const Vector3r & emitDir = m_rotation.col(0);
    Simulation *sim = Simulation::getCurrent();
    const Real particleRadius = sim->getParticleRadius();
    const Real diam = static_cast<Real>(2.0)*particleRadius;
    Vector3r emitVel = m_velocity * emitDir;

    // shortly before the emitter starts, cleanup the emitter from particles
    if (t < m_emitStartTime || t > m_emitEndTime)
        emitVel = emitDir * particleRadius * 10 / 0.25;

    if (t >= m_emitStartTime - 0.25 && t <= m_emitEndTime)
    {
        // animate emitted particles
        const Vector3r & x0 = m_x;

        const Real animationMarginAhead = sim->getSupportRadius();
        const Vector3r size = getSize(static_cast<Real>(m_width), static_cast<Real>(m_height), m_type);
        const Real h = size[0];
        const Real r = 0.5f * size[1];
        const Real r2 = r * r;
        const Vector3r pos = x0 + 0.5f * animationMarginAhead * emitDir;
}
```

--------------------------------

### Pressure solve iteration setup

Source: https://splishsplash.readthedocs.io/en/latest/api/program_listing_file_SPlisHSPlasH_IISPH_TimeStepIISPH.cpp.html

Sets up a single pressure solve iteration: retrieves simulation data, checks for active particles, and initializes the dij_pj vector for each particle. Uses OpenMP parallelization.

```cpp
void TimeStepIISPH::pressureSolveIteration(const unsigned int fluidModelIndex, Real &avg_density_err)
{
    Simulation *sim = Simulation::getCurrent();
    FluidModel *model = sim->getFluidModel(fluidModelIndex);
    const unsigned int numParticles = model->numActiveParticles();
    if (numParticles == 0)
        return;

    const unsigned int nFluids = sim->numberOfFluidModels();
    const unsigned int nBoundaries = sim->numberOfBoundaryModels();

    const Real density0 = model->getDensity0();
    const Real h = TimeManager::getCurrent()->getTimeStepSize();
    const Real h2 = h*h;
    const Real omega = 0.5;

    // Compute dij_pj
    #pragma omp parallel default(shared)
    {
        #pragma omp for schedule(static)
        for (int i = 0; i < (int)numParticles; i++)
        {
            Vector3r &dij_pj = m_simulationData.getDij_pj(fluidModelIndex, i);
            dij_pj.setZero();

            const Vector3r &xi = model->getPosition(i);
```

--------------------------------

### Install Python bindings with pip

Source: https://splishsplash.readthedocs.io/en/latest/getting_started.html

Clone the SPlisHSPlasH repository and install the Python bindings using pip. It is recommended to use a virtual environment because cache files, models, and scene files are stored in the Python installation directory.

```bash
git clone https://github.com/InteractiveComputerGraphics/SPlisHSPlasH.git
pip install SPlisHSPlasH/
```

--------------------------------

### Install numpy dependency

Source: https://splishsplash.readthedocs.io/en/latest/py_getting_started.html

Installs numpy, which may be required for the bindings. Future releases may include it as a dependency.

```bash
pip install numpy
```

--------------------------------

### step()

Source: https://splishsplash.readthedocs.io/en/latest/api/class_s_p_h_1_1_surface_tension___becker2007.html

Performs a simulation step for the surface tension method.

```APIDOC
## step()

### Description
Performs a simulation step for the surface tension method.

### Method
virtual void step()

```

--------------------------------

### Install Ubuntu dependencies for SPlisHSPlasH

Source: https://splishsplash.readthedocs.io/en/latest/build_from_source.html

Installs required packages for building SPlisHSPlasH on Ubuntu: git, cmake, Xorg development files, freeglut3, and build-essential.

```bash
sudo apt install git cmake xorg-dev freeglut3-dev build-essential
```

--------------------------------

### TimeStepPF Parameter Initialization

Source: https://splishsplash.readthedocs.io/en/latest/api/program_listing_file_SPlisHSPlasH_PF_TimeStepPF.cpp.html

Sets up the maxError and stiffness parameters for the projective fluids simulation, including their groups, descriptions, and minimum values.

```cpp
MAX_ERROR = createNumericParameter("maxError", "Max. error", &m_maxError);
    setGroup(MAX_ERROR, "Simulation|Projective Fluids");
    setDescription(MAX_ERROR, "Maximal error.");
    static_cast<RealParameter*>(getParameter(MAX_ERROR))->setMinValue(static_cast<Real>(1e-12));

    STIFFNESS = createNumericParameter("stiffness", "Stiffness", &m_stiffness);
    setGroup(STIFFNESS, "Simulation|Projective Fluids");
    setDescription(STIFFNESS, "Stiffness coefficient.");
    static_cast<RealParameter*>(getParameter(STIFFNESS))->setMinValue(static_cast<Real>(1e-6));
}
```

--------------------------------

### Setup Material Type Parameter for Elasticity_Kee2023

Source: https://splishsplash.readthedocs.io/en/latest/api/program_listing_file_SPlisHSPlasH_Elasticity_Elasticity_Kee2023.cpp.html

Configures the 'materialType' enum parameter with options 'Stable Neo-Hookean' and 'Co-rotated'. This is part of the Elasticity_Kee2023 class setup.

```C++
MATERIAL_TYPE = createEnumParameter("materialType", "Material type", &m_materialType);
    setGroup(MATERIAL_TYPE, "Fluid Model|Elasticity");
    setDescription(MATERIAL_TYPE, "Constitutive model for the elastic material.");
    enumParam = static_cast<EnumParameter*>(getParameter(MATERIAL_TYPE));
    enumParam->addEnumValue("Stable Neo-Hookean", ENUM_MATERIAL_STABLE_NEOHOOKEAN);
    enumParam->addEnumValue("Co-rotated", ENUM_MATERIAL_COROTATED);
}
```

--------------------------------

### void EmitterSystem::step()

Source: https://splishsplash.readthedocs.io/en/latest/api/class_s_p_h_1_1_emitter_system.html

Advances the emitter system by one simulation step.

```APIDOC
## void EmitterSystem::step()

### Description
Advances the emitter system by one simulation step.

```

--------------------------------

### initKernels

Source: https://splishsplash.readthedocs.io/en/latest/api/class_s_p_h_1_1_simulation.html

Initializes the kernel functions used in the simulation.

```APIDOC
## initKernels

### Description
Initializes the kernel functions used in the simulation.

### Method
`void initKernels()`
```

--------------------------------

### TimeStepPBF::resize()

Source: https://splishsplash.readthedocs.io/en/latest/api/program_listing_file_SPlisHSPlasH_PBF_TimeStepPBF.cpp.html

Initializes the simulation data by calling its init() method.

```cpp
void TimeStepPBF::resize()
{
    m_simulationData.init();
}
```

--------------------------------

### initFactorization

Source: https://splishsplash.readthedocs.io/en/latest/api/class_s_p_h_1_1_elasticity___kugelstadt2021.html

Initializes the solver for the linear system by either computing a factorization or loading a factorization from the cache.

```APIDOC
## initFactorization

### Description
Initializes the solver for the linear system by either computing a factorization or loading a factorization from the cache.

### Method
void initFactorization(std::shared_ptr<Factorization> factorization, std::vector<unsigned int> &particleIndices, const unsigned int nFixed, const Real dt, const Real mu)

### Parameters
- **factorization** (std::shared_ptr<Factorization>) - Required - The factorization object to use.
- **particleIndices** (std::vector<unsigned int>&) - Required - Indices of particles involved.
- **nFixed** (unsigned int) - Required - Number of fixed particles.
- **dt** (Real) - Required - Time step size.
- **mu** (Real) - Required - Shear modulus.

### Description
Compute the factorization of the linear system matrix. This is only done once at the beginning of the simulation.
```

--------------------------------

### FluidModels JSON configuration example

Source: https://splishsplash.readthedocs.io/en/latest/file_format.html

Imports a partio particle file (bunny.bgeo) with translation, rotation axis, rotation angle, and scale. The particleFile can also be an OBJ mesh that is automatically sampled.

```json
"FluidModels": [
    {
        "particleFile": "../models/bunny.bgeo",
        "translation": [-2.0, 0.1, 0.0],
        "rotationAxis": [0, 1, 0],
        "rotationAngle": 3.14159265359,
        "scale": 1
    }
]
```

--------------------------------

### RigidBodies JSON example

Source: https://splishsplash.readthedocs.io/en/latest/file_format.html

Example JSON configuration for a rigid body in a SplishSplash scene file. It shows a static wall with a box geometry, translation, rotation, scale, color, and sampling mode. The parameters are described in the surrounding documentation.

```json
{
    "RigidBodies": [
        {
            "geometryFile": "../models/UnitBox.obj",
            "translation": [0,2,0],
            "rotationAxis": [1, 0, 0],
            "rotationAngle": 0,
            "scale": [2.5, 4, 1.0],
            "color": [0.1, 0.4, 0.6, 1.0], 
            "isDynamic": false,
            "isWall": true,
            "mapInvert": true, 
            "mapThickness": 0.0,
            "mapResolution": [20,20,20],
            "samplingMode": 1
        }
    ]
}
```

--------------------------------

### setEmitStartTime

Source: https://splishsplash.readthedocs.io/en/latest/api/class_s_p_h_1_1_emitter.html

Sets the start time for particle emission.

```APIDOC
## void setEmitStartTime(Real val)

### Description
Sets the start time for particle emission.

### Parameters
- **val** (Real) - Required - The emission start time.
```

--------------------------------

### Explicit simulation commands replacing base.run()

Source: https://splishsplash.readthedocs.io/en/latest/py_creating_scenes.html

Shows the three commands that base.run() is a shortcut for: initSimulation, runSimulation, and cleanup. Use these when you need to change parameters after initialization.

```python
   base.initSimulation()       # init simulation, fluid models, time step, ...
   base.runSimulation()        # start the simulation
   base.cleanup()              # cleanup everything after the simulation
```

--------------------------------

### setStartTime

Source: https://splishsplash.readthedocs.io/en/latest/api/class_s_p_h_1_1_animation_field.html

Sets the start time of the animation field.

```APIDOC
## void setStartTime(Real val)

### Description
Sets the start time of the animation field.

### Parameters
- **val** (Real) - Required - The start time value.
```

--------------------------------

### FileSystem.h header with path utilities and makeDir

Source: https://splishsplash.readthedocs.io/en/latest/api/program_listing_file_Utilities_FileSystem.h.html

Full source of Utilities/FileSystem.h. Provides static methods getFilePath, getFileName, getFileNameWithExt, getFileExt, isRelativePath, and makeDir. Includes platform-specific headers and S_ISDIR/S_ISREG macros. makeDir uses _mkdir on WIN32 and mkdir with S_IRWXU|S_IRWXG|S_IROTH|S_IXOTH elsewhere, returning -1 on failure unless errno is EEXIST.

```cpp
#ifndef __FileSystem_h__
#define __FileSystem_h__

#include "StringTools.h"
#include "extern/md5/md5.h"
#include <sys/stat.h>
#ifdef WIN32
#include <direct.h>
#define NOMINMAX
#include "windows.h"
#include <commdlg.h>
#else
#include <unistd.h>
#include <dirent.h>
#endif
#ifdef __APPLE__
#include <mach-o/dyld.h>
#endif

#ifndef S_ISDIR
#define S_ISDIR(mode)  (((mode) & S_IFMT) == S_IFDIR)
#endif

#ifndef S_ISREG
#define S_ISREG(mode)  (((mode) & S_IFMT) == S_IFREG)
#endif

namespace Utilities
{
    class FileSystem
    {
    public:

        static std::string getFilePath(const std::string &path)
        {
            std::string npath = normalizePath(path);

            std::string result = npath;
            size_t i = result.rfind('.', result.length());
            if (i != std::string::npos)
            {
                result = result.substr(0, i);
            }
            size_t p1 = result.rfind('\\', result.length());
            size_t p2 = result.rfind('/', result.length());
            if ((p1 != std::string::npos) && (p2 != std::string::npos))
                result = result.substr(0, std::max(p1, p2));
            else if (p1 != std::string::npos)
                result = result.substr(0, p1);
            else if (p2 != std::string::npos)
                result = result.substr(0, p2);
            return result;
        }

        static std::string getFileName(const std::string &path)
        {
            std::string npath = normalizePath(path);

            std::string result = npath;
            size_t i = result.rfind('.', result.length());
            if (i != std::string::npos)
            {
                result = result.substr(0, i);
            }
            size_t p1 = result.rfind('\\', result.length());
            size_t p2 = result.rfind('/', result.length());
            if ((p1 != std::string::npos) && (p2 != std::string::npos))
                result = result.substr(std::max(p1, p2) + 1, result.length());
            else if (p1 != std::string::npos)
                result = result.substr(p1 + 1, result.length());
            else if (p2 != std::string::npos)
                result = result.substr(p2 + 1, result.length());
            return result;
        }

        static std::string getFileNameWithExt(const std::string &path)
        {
            std::string npath = normalizePath(path);

            std::string result = npath;
            size_t p1 = result.rfind('\\', result.length());
            size_t p2 = result.rfind('/', result.length());
            if ((p1 != std::string::npos) && (p2 != std::string::npos))
                result = result.substr(std::max(p1, p2) + 1, result.length());
            else if (p1 != std::string::npos)
                result = result.substr(p1 + 1, result.length());
            else if (p2 != std::string::npos)
                result = result.substr(p2 + 1, result.length());
            return result;
        }

        static std::string getFileExt(const std::string &path)
        {
            std::string npath = normalizePath(path);

            std::string result = npath;
            size_t i = result.rfind('.', result.length());
            if (i != std::string::npos)
            {
                result = result.substr(i + 1, result.length());
            }
            return result;
        }

        static bool isRelativePath(const std::string &path)
        {
            std::string npath = normalizePath(path);

            // Windows
            size_t i = npath.find(":");
            if (i != std::string::npos)
                return false;
            else if (npath[0] == '/')
                return false;
            return true;
        }

        static int makeDir(const std::string &path)
        {
            std::string npath = normalizePath(path);

            struct stat st;
            int status = 0;

            if (stat(path.c_str(), &st) != 0)
            {
#if WIN32
                status = _mkdir(path.c_str());
#else
                status = mkdir(path.c_str(), S_IRWXU | S_IRWXG | S_IROTH | S_IXOTH);
#endif
                if (status != 0 && errno != EEXIST)
                    status = -1;
            }
            else if (!(S_IFDIR & st.st_mode))
            {
                errno = ENOTDIR;
                status = -1;
            }

            return status;
        }
```

--------------------------------

### Example embedded Python script for SplishSplash

Source: https://splishsplash.readthedocs.io/en/latest/py_embedded_python.html

A complete example script that prints the current simulation time, the position of particle 0, and a counter value in each step. It defines the required init, step, and reset functions, plus two additional commands.

```python
import splishsplash as sph
import numpy as np

counter = 0
function_list = ['command', 'command2']

def init(base):
    global counter
    print("init test")
    counter = 1
    
def step():
    global counter
    sim = sph.Simulation.getCurrent()
    fluid = sim.getFluidModel(0)
    tm = sph.TimeManager.getCurrent()
    print(fluid.getPosition(0))
    print(tm.getTime())
    print(counter)
    counter += 1
    print("---")
    
def reset():
    print("reset test")
    
def command():
    print("tst cmd")
        
def command2():
    print("tst cmd2")
```

--------------------------------

### Show splash help

Source: https://splishsplash.readthedocs.io/en/latest/py_getting_started.html

Displays the help for the splash command, showing available options and functionality.

```bash
splash --help
```

--------------------------------

### TimeStepDFSPH::pressureSolve() implementation

Source: https://splishsplash.readthedocs.io/en/latest/api/program_listing_file_SPlisHSPlasH_DFSPH_TimeStepDFSPH.cpp.html

Full implementation of the DFSPH pressure solver. Computes rho_adv, applies warm start or direct pressure computation, iterates until convergence or max iterations, updates velocities with pressure accelerations, and optionally scales pressure for warm start.

```cpp
void TimeStepDFSPH::pressureSolve()
{
    const Real h = TimeManager::getCurrent()->getTimeStepSize();
    const Real h2 = h*h;
    const Real invH = static_cast<Real>(1.0) / h;
    const Real invH2 = static_cast<Real>(1.0) / h2;
    Simulation *sim = Simulation::getCurrent();
    const unsigned int nFluids = sim->numberOfFluidModels();

    // Compute rho_adv
    for (unsigned int fluidModelIndex = 0; fluidModelIndex < nFluids; fluidModelIndex++)
    {
        FluidModel *model = sim->getFluidModel(fluidModelIndex);
        const Real density0 = model->getDensity0();
        const int numParticles = (int)model->numActiveParticles();
        #pragma omp parallel default(shared)
        {
            #pragma omp for schedule(static)
            for (int i = 0; i < numParticles; i++)
            {
                // Compute rho_adv,i^(0) (see equation in Section 3.3 in [BK17])
                // using the velocities after the non-pressure forces were applied.
                computeDensityAdv(fluidModelIndex, i, h, density0);

                // In the end of Section 3.3 [BK17] we have to multiply the density
                // error with the factor alpha_i divided by h^2. Hence, we multiply
                // the factor directly by 1/h^2 here.
                m_simulationData.getFactor(fluidModelIndex, i) *= invH2;

                // For the warm start we use 0.5 times the old pressure value.
                // Note: We divide the value by h^2 since we multiplied it by h^2 at the end of
                // the last time step to make it independent of the time step size.
#ifdef USE_WARMSTART
                if (m_simulationData.getDensityAdv(fluidModelIndex, i) > 1.0)
                    m_simulationData.getPressureRho2(fluidModelIndex, i) = static_cast<Real>(0.5) * min(m_simulationData.getPressureRho2(fluidModelIndex, i), static_cast<Real>(0.00025)) * invH2;
                else
                    m_simulationData.getPressureRho2(fluidModelIndex, i) = 0.0;
#else
                // If we don't use a warm start, we directly compute a pressure value
                // by multiplying the density error with the factor.
                //m_simulationData.getPressureRho2(fluidModelIndex, i) = 0.0;
                const Real s_i = static_cast<Real>(1.0) - m_simulationData.getDensityAdv(fluidModelIndex, i);
                const Real residuum = min(s_i, static_cast<Real>(0.0));     // r = b - A*p
                m_simulationData.getPressureRho2(fluidModelIndex, i) = -residuum * m_simulationData.getFactor(fluidModelIndex, i);
#endif
            }
        }
    }

    m_iterations = 0;

    // Start solver

    Real avg_density_err = 0.0;
    bool chk = false;


    // Perform solver iterations
    while ((!chk || (m_iterations < m_minIterations)) && (m_iterations < m_maxIterations))
    {
        chk = true;
        for (unsigned int i = 0; i < nFluids; i++)
        {
            FluidModel *model = sim->getFluidModel(i);
            const Real density0 = model->getDensity0();

            avg_density_err = 0.0;
            pressureSolveIteration(i, avg_density_err);

            // Maximal allowed density fluctuation
            const Real eta = m_maxError * static_cast<Real>(0.01) * density0;  // maxError is given in percent
            chk = chk && (avg_density_err <= eta);
        }

        m_iterations++;
    }

    INCREASE_COUNTER("DFSPH - iterations", static_cast<Real>(m_iterations));

    for (unsigned int fluidModelIndex = 0; fluidModelIndex < nFluids; fluidModelIndex++)
    {
        FluidModel *model = sim->getFluidModel(fluidModelIndex);
        const int numParticles = (int)model->numActiveParticles();
        const Real density0 = model->getDensity0();

        #pragma omp parallel default(shared)
        {
            #pragma omp for schedule(static)
            for (int i = 0; i < numParticles; i++)
            {
                // Time integration of the pressure accelerations to get new velocities
                computePressureAccel(fluidModelIndex, i, density0, m_simulationData.getPressureRho2Data(), true);
                model->getVelocity(i) += h * m_simulationData.getPressureAccel(fluidModelIndex, i);
            }
        }
    }
#ifdef USE_WARMSTART
    for (unsigned int fluidModelIndex = 0; fluidModelIndex < nFluids; fluidModelIndex++)
    {
        FluidModel* model = sim->getFluidModel(fluidModelIndex);
        const int numParticles = (int)model->numActiveParticles();
        #pragma omp parallel default(shared)
        {
            #pragma omp for schedule(static)
            for (int i = 0; i < numParticles; i++)
            {
                // Multiply by h^2, the time step size has to be removed
                // to make the pressure value independent
                // of the time step size
                m_simulationData.getPressureRho2(fluidModelIndex, i) *= h2;
            }
        }
    }
#endif
}
```

--------------------------------

### void initModel(RigidBodyObject *rbo)

Source: https://splishsplash.readthedocs.io/en/latest/api/class_s_p_h_1_1_boundary_model___bender2019.html

Initializes the boundary model with a rigid body object.

```APIDOC
## void initModel(RigidBodyObject *rbo)

### Description
Initializes the boundary model with a rigid body object.

### Method
void initModel(RigidBodyObject *rbo)

### Parameters
- **rbo** (RigidBodyObject*) - Required - Pointer to the rigid body object.

### Returns
None
```

--------------------------------

### FluidModel::init()

Source: https://splishsplash.readthedocs.io/en/latest/api/class_s_p_h_1_1_fluid_model.html

Initializes the fluid model.

```APIDOC
## FluidModel::init()

### Description
Initializes the fluid model.

### Method
void init()

### Parameters
None

### Returns
void
```

--------------------------------

### Elasticity_Kee2023::newtonMatvec (USE_AVX) - start of matrix-vector product

Source: https://splishsplash.readthedocs.io/en/latest/api/program_listing_file_SPlisHSPlasH_Elasticity_Elasticity_Kee2023.cpp.html

Starts the implementation of the Newton matrix-vector product under the USE_AVX macro. It retrieves particle indices, counts free particles, and obtains references to the AVX vectors p_avx and Ap_avx. The code is incomplete as shown, ending after the variable declarations.

```cpp
#ifdef USE_AVX
void Elasticity_Kee2023::newtonMatvec(ElasticObject* obj)
{
    const std::vector<unsigned int>& group = obj->m_particleIndices;
    const int numParticles = (int)group.size();
    const int nFree = numParticles - (int)obj->m_nFixed;
    auto& p_avx = obj->m_pcg_p_avx;
    auto& Ap_avx = obj->m_pcg_Ap_avx;
```

--------------------------------

### TimeStepMyPressureSolve.cpp - Minimal Implementation for Custom Pressure Solver

Source: https://splishsplash.readthedocs.io/en/latest/creating_pressure.html

Source file for the custom pressure solver class. It implements the constructor, destructor, step(), and resize() methods. The step() method defines the simulation algorithm and is called by the main loop.

```cpp
#include "TimeStepMyPressureSolve.h"

using namespace SPH;
using namespace GenParam;

TimeStepMyPressureSolve::TimeStepMyPressureSolve() :
    TimeStep()
{
    [...]
}

TimeStepMyPressureSolve::~TimeStepMyPressureSolve(void)
{
    [...]
}

void TimeStepMyPressureSolve::step()
{
    [...]
}

void TimeStepMyPressureSolve::resize()
{
    [...]
}
```

--------------------------------

### SPH::AnimationField::setStartTime

Source: https://splishsplash.readthedocs.io/en/latest/genindex.html

Sets the start time for the animation field.

```APIDOC
## SPH::AnimationField::setStartTime

### Description
Sets the start time for the animation field.

### Method
C++ function

### Signature
`void SPH::AnimationField::setStartTime(Real startTime)`

### Parameters
- `startTime` (Real) - Required - The start time value.

```

--------------------------------

### setNumActiveParticles0

Source: https://splishsplash.readthedocs.io/en/latest/api/class_s_p_h_1_1_fluid_model.html

Sets the number of active particles at the start of the simulation step.

```APIDOC
## setNumActiveParticles0(unsigned int val)

### Description
Sets the number of active particles at the start of the simulation step.

### Method
C++ member function (inline)

### Signature
`inline void setNumActiveParticles0(unsigned int val)`

### Parameters
- **val** (unsigned int) - Required - The new number of active particles at the start of the step.

```

--------------------------------

### Simulation.cpp: Handle new pressure solver in setSimulationMethod

Source: https://splishsplash.readthedocs.io/en/latest/creating_pressure.html

Adds a branch in Simulation::setSimulationMethod(...) to instantiate the new TimeStepMyPressureSolver, initialize it, and set the desired standard SPH kernel and gradient kernel.

```cpp
else if (method == SimulationMethods::MyPressureSolver)
{
    m_timeStep = new TimeStepMyPressureSolver();
    m_timeStep->init();
    setValue(Simulation::KERNEL_METHOD, <desired standard SPH kernel>);
    setValue(Simulation::GRAD_KERNEL_METHOD, <desired standard SPH gradient kernel>);
}
```

--------------------------------

### getNumActiveParticles0

Source: https://splishsplash.readthedocs.io/en/latest/api/class_s_p_h_1_1_fluid_model.html

Returns the number of active particles at the start of the simulation step.

```APIDOC
## getNumActiveParticles0() const

### Description
Returns the number of active particles at the start of the simulation step.

### Method
C++ member function (inline, const)

### Signature
`inline unsigned int getNumActiveParticles0() const`

### Returns
- **unsigned int** - The number of active particles at the start of the step.

```

--------------------------------

### void step()

Source: https://splishsplash.readthedocs.io/en/latest/api/class_s_p_h_1_1_debug_tools.html

Performs a simulation step for debugging purposes.

```APIDOC
## void step()

### Description
Performs a simulation step for debugging purposes.

### Method
Member function

### Signature
`void step()`

```
Tokens:
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