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Clean up
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@Zang3th
Zang3th committed May 16, 2024
1 parent bb040e9 commit 1dd133b
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Showing 6 changed files with 39 additions and 92 deletions.
4 changes: 2 additions & 2 deletions Apps/Liquefied/LiquefiedApp.cpp
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Expand Up @@ -59,8 +59,8 @@ namespace Liq
_fluidSimulator = Engine::MakeScope<Engine::FluidSimulator>();

//Create timer
_physicsTimer = Engine::MakeScope<Engine::Timer>(8); //8ms
_inputTimer = Engine::MakeScope<Engine::Timer>(100); //100ms
_physicsTimer = Engine::MakeScope<Engine::Timer>(16); //16ms
_inputTimer = Engine::MakeScope<Engine::Timer>(100); //100ms

//Add border cells to simulation and renderer
AddBorderCells();
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3 changes: 2 additions & 1 deletion Apps/Liquefied/LiquefiedInterface.cpp
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Expand Up @@ -47,8 +47,9 @@ namespace Liq
{
ImGui::NewLine();
ImGui::RadioButton("Forward Euler", (int*)&Engine::LiquiefiedParams::integratorChoice, Engine::Integrator::ForwardEuler);
ImGui::RadioButton("Modified Forward Euler", (int*)&Engine::LiquiefiedParams::integratorChoice, Engine::Integrator::ModifiedForwardEuler);
ImGui::RadioButton("Backward Euler", (int*)&Engine::LiquiefiedParams::integratorChoice, Engine::Integrator::BackwardEuler);
ImGui::RadioButton("Runge Kutta 2", (int*)&Engine::LiquiefiedParams::integratorChoice, Engine::Integrator::RungeKutta2);
ImGui::RadioButton("Runge Kutta 3", (int*)&Engine::LiquiefiedParams::integratorChoice, Engine::Integrator::RungeKutta3);
ImGui::RadioButton("Semi Lagrangian", (int*)&Engine::LiquiefiedParams::integratorChoice, Engine::Integrator::SemiLagrangian);
ImGui::EndTabItem();
}
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5 changes: 3 additions & 2 deletions Engine/Application/GlobalParams.hpp
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Expand Up @@ -155,9 +155,10 @@ namespace Engine
enum Integrator
{
ForwardEuler = 0,
ModifiedForwardEuler = 1,
BackwardEuler = 1,
RungeKutta2 = 2,
SemiLagrangian = 3,
RungeKutta3 = 3,
SemiLagrangian = 4,
};

enum Visualization
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106 changes: 25 additions & 81 deletions Engine/Physics/FluidSimulation/FluidSimulator.cpp
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Expand Up @@ -39,9 +39,9 @@ namespace Engine

/* Projection calculates and applies the right amount of pressure to make the *
* velocity field divergence-free and also enforces solid wall boundary conditions. */
void FluidSimulator::Project(const float dt) const
void FluidSimulator::Project() const
{
//Simple solution using Gauss-Seidel
//Solve iteratively using Gauss-Seidel
for(uint32 it = 0; it < ITER; it++)
{
for(uint32 x = 1; x < _grid.width-1; x++)
Expand Down Expand Up @@ -127,31 +127,35 @@ namespace Engine
{
float uAdvect = 0.0f, vAdvect = 0.0f;

/* Iterate over grid and update all velocities according to the chosen numerical integrator. */
//Iterate over grid and update all velocities according to the chosen numerical integrator
for(uint32 x = 1; x < _grid.width-1; x++)
{
for(uint32 y = 1; y < _grid.height-1; y++)
{
/* Skip border cells. */
//Skip border cells
if(_grid.b[AT(x, y)] == 0 || _grid.b[AT(x-1, y)] == 0 || _grid.b[AT(x, y-1)] == 0 || _grid.b[AT(x+1, y)] == 0 || _grid.b[AT(x, y+1)] == 0)
{
continue;
}

/* Calculate u- and v-velocity depending on the chosen integrator. */
//Calculate u- and v-velocity depending on the chosen integrator
if(LiquiefiedParams::integratorChoice == Integrator::ForwardEuler)
{
uAdvect = ForwardEuler(dt, _grid.u_Avg(x, y), _grid.u[AT(x, y)], _grid.u[AT(x+1, y)], _grid.u[AT(x-1, y)]);
vAdvect = ForwardEuler(dt, _grid.v_Avg(x, y), _grid.v[AT(x, y)], _grid.v[AT(x, y+1)], _grid.v[AT(x, y-1)]);
}
else if(LiquiefiedParams::integratorChoice == Integrator::ModifiedForwardEuler)
else if(LiquiefiedParams::integratorChoice == Integrator::BackwardEuler)
{
//...
}
else if(LiquiefiedParams::integratorChoice == Integrator::RungeKutta2)
{
//...
}
else if(LiquiefiedParams::integratorChoice == Integrator::RungeKutta3)
{
//...
}
else if(LiquiefiedParams::integratorChoice == Integrator::SemiLagrangian)
{
const float h = _grid.h;
Expand Down Expand Up @@ -235,14 +239,18 @@ namespace Engine
density = std::abs((uAdvect + vAdvect) * 0.5f);
density = std::min(density, 1.0f);
}
else if(LiquiefiedParams::integratorChoice == Integrator::ModifiedForwardEuler)
else if(LiquiefiedParams::integratorChoice == Integrator::BackwardEuler)
{
//...
}
else if(LiquiefiedParams::integratorChoice == Integrator::RungeKutta2)
{
//...
}
else if(LiquiefiedParams::integratorChoice == Integrator::RungeKutta3)
{
//...
}
else if(LiquiefiedParams::integratorChoice == Integrator::SemiLagrangian)
{
const float h = _grid.h;
Expand Down Expand Up @@ -273,7 +281,7 @@ namespace Engine
}

/* Returns false if integrator got unstable. */
bool FluidSimulator::CheckCFLStability(float dt, float value) const
bool FluidSimulator::CheckCFLStability(const float dt, const float value) const
{
//Check numerical stability via CFL condition (Courant–Friedrichs–Lewy condition)
const float cfl = (value * dt) / (float)_grid.dx;
Expand Down Expand Up @@ -334,12 +342,7 @@ namespace Engine
return velocity;
}

float FluidSimulator::ModifiedForwardEuler() const
{
return 0;
}

float FluidSimulator::BackwardEuler(const float dt, const float vel, const float* q_values, const uint32 q_startX, const uint32 q_startY) const
float FluidSimulator::BackwardEuler() const
{
/* The update rule for Backward-Euler looks like this: *
* *
Expand All @@ -358,35 +361,6 @@ namespace Engine
* For linear problems, direct algebraic manipulation may suffice. *
* For nonlinear problems, iterative methods are commonly used. *
* *
* Let's start by discretizing Backward-Euler: *
* *
* (2.) q1[i] = q0[i] + dt * f(q1[i]) *
* *
* We can formulate Backward-Euler as a root finding problem: *
* *
* (3.) F = q1[i] - q0[i] - dt * f(q1[i]) = 0 *
* *
* For an equation like this we can use the Newton-Raphson method. *
* The update rule for Newton-Raphson looks like this: *
* *
* (4.) x_new = x_old - f(x_old) / f'(x_old) *
* *
* - x_new := Approximated value for the next iteration. *
* - x_old := Value at the current iteration. *
* - f(x_old) := Value of f at the point x_old. *
* - f'(x_old) := Derivative of f at the point x_old. *
* *
* This involves guessing an initial value for x_new (like x0), *
* computing the derivative of f with respect to x_old, and *
* iteratively refining x_new until the change becomes very small. *
* *
* Algorithmic steps: *
* *
* 1. Calculate a satisfying approximation for f(x1) with *
* the Newton-Raphson method. *
* 2. Insert f(x1) back into the Backward-Euler update rule to *
* calculate the value for the next timestep. *
* *
* With the cost of this additional computational effort comes *
* the advantage of way higher stability and robustness than with *
* Forward-Euler. *
Expand All @@ -395,47 +369,17 @@ namespace Engine
* Source: Cornell University - CS3220 Lecture Notes *
* https://www.cs.cornell.edu/~bindel/class/cs3220-s12/lectures.html */

const uint32 dx = _grid.dx;
const uint32 x1 = NewtonRaphson(q_values, q_startX, q_startY, 5);
const float f_x1 = (q_values[x1+dx] - q_values[x1-dx]) / (float)(2 * dx);
const float x0 = q_values[AT(q_startX, q_startY)];

const float velocity = x0 - dt * vel * f_x1;

return velocity;
return 0.0f;
}

uint32 FluidSimulator::NewtonRaphson(const float* values, const uint32 startX, const uint32 startY, const uint32 maxIteration) const
float FluidSimulator::RungeKutta2() const
{
/* The update rule for Newton-Raphson looks like this: *
* *
* x1 = x0 - f(x0) / f'(x0) *
* *
* - x1 := Approximated x-value for the next iteration. *
* - x0 := x-value at the current iteration. *
* - f(x0) := Value of f at the point x0. *
* - f'(x0) := Derivative of f at the point x0. *
* *
* We will use a central derivative approximation just like before. */

const uint32 dx = _grid.dx;
float f_x0 = 0.0f, f_x1 = 0.0f;
uint32 x1 = 0, x0 = AT(startX, startY);

for(uint32 iter = 0; iter < maxIteration; iter++)
{
f_x0 = values[x0];
f_x1 = (values[x0+dx] - values[x0-dx]) / (float)(2 * dx);
x1 = x0 - (uint32)(f_x0 / f_x1);

//Check convergence, break if value didn't change
if(x1 == x0)
break;

x0 = x1;
}
return 0.0f;
}

return x1;
float FluidSimulator::RungeKutta3() const
{
return 0.0f;
}

// ----- Public -----
Expand All @@ -455,7 +399,7 @@ namespace Engine
}
{
PROFILE_SCOPE("#Project");
Project(dt);
Project();
}
{
PROFILE_SCOPE("#Extrapolate");
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8 changes: 4 additions & 4 deletions Engine/Physics/FluidSimulation/FluidSimulator.hpp
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Expand Up @@ -18,15 +18,15 @@ namespace Engine

void Init() const;
void AddForces(float dt) const;
void Project(float dt) const;
void Project() const;
void Extrapolate() const;
void AdvectVelocity(float dt);
void AdvectSmoke(float dt);
[[nodiscard]] bool CheckCFLStability(float dt, float value) const;
[[nodiscard]] float ForwardEuler(float dt, float u, float q, float q_next, float q_prev) const;
[[nodiscard]] float ModifiedForwardEuler() const;
[[nodiscard]] float BackwardEuler(float dt, float vel, const float* q_values, uint32 q_startX, uint32 q_startY) const;
[[nodiscard]] uint32 NewtonRaphson(const float* values, uint32 startX, uint32 startY, uint32 maxIteration) const;
[[nodiscard]] float BackwardEuler() const;
[[nodiscard]] float RungeKutta2() const;
[[nodiscard]] float RungeKutta3() const;

public:
FluidSimulator();
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5 changes: 3 additions & 2 deletions README.md
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Expand Up @@ -28,6 +28,7 @@ SalinityGL is licensed under the [MIT LICENSE](https://github.com/Zang3th/GameEn
│ ├── Application/ # Application and interface stuff
│ ├── Core/ # Utilities and core engine functionalities
│ ├── Debug/ # Logging and error handling
├── Phyics/ # Code for cellular automata and fluid simulation
│ ├── Rendering/ # GL stuff, buffers, renderer ...
│ └── Engine.hpp # Main header for include in the applications
├── Res/ # Assets, sounds and screenshots
Expand Down Expand Up @@ -147,8 +148,8 @@ I always work *on and off* on this project, but I try to make more regular relea

### Backlog

- Grass simulation
- Some raytracing project
- 3D fluid simulation
- Some kind of raytracing project

## External libraries

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