resonance.c

#include "common.h"

//--------------------------------------

float spring_energy(
    float x, 
    float v, 
    float frequency,
    float x_rest = 0.0f, 
    float v_rest = 0.0f,
    float scale = 1.0f)
{
    float s = frequency_to_stiffness(frequency);
    
    return (
        squaref(scale * (v - v_rest)) + s * 
        squaref(scale * (x - x_rest))) / 2.0f;
}

float resonant_frequency(float goal_frequency, float halflife)
{
    float d = halflife_to_damping(halflife);
    float goal_stiffness = frequency_to_stiffness(goal_frequency);
    float resonant_stiffness = goal_stiffness - (d*d)/4.0f;
    return stiffness_to_frequency(resonant_stiffness);
}

//--------------------------------------

enum
{
    HISTORY_MAX = 256
};

float x_prev[HISTORY_MAX];
float v_prev[HISTORY_MAX];
float t_prev[HISTORY_MAX];
float g_prev[HISTORY_MAX];

int main(void)
{
    // Init Window
    
    const int screenWidth = 640;
    const int screenHeight = 360;

    InitWindow(screenWidth, screenHeight, "raylib [springs] example - resonance");

    // Init Variables

    float t = 0.0;
    float x = screenHeight / 2.0f;
    float v = 0.0;
    float g = x;
    float goalOffset = 600;

    float frequency = 2.0f;
    float halflife = 2.0f;
    float dt = 1.0 / 60.0f;
    float timescale = 240.0f;

    float goal_frequency = 2.5f;
    float res_frequency = 1.5f;
    float energy = 0.0;
    
    SetTargetFPS(1.0f / dt);

    for (int i = 0; i < HISTORY_MAX; i++)
    {
        x_prev[i] = x;
        v_prev[i] = v;
        t_prev[i] = t;
        g_prev[i] = x;
    }
    
    while (!WindowShouldClose())
    {
        // Shift History
        
        for (int i = HISTORY_MAX - 1; i > 0; i--)
        {
            x_prev[i] = x_prev[i - 1];
            v_prev[i] = v_prev[i - 1];
            t_prev[i] = t_prev[i - 1];
            g_prev[i] = g_prev[i - 1];
        }
        
        // Get Goal
        
        g = screenHeight / 2.0f + 10.0 * sinf(t * 2.0f * M_PI * goal_frequency);
        
        // Resonance
        
        if (GuiButton((Rectangle){ 125, 95, 120, 20 }, "Resonant Frequency"))
        {
            frequency = resonant_frequency(goal_frequency, halflife);
        }

        GuiSliderBar((Rectangle){ 125, 20, 120, 20 }, "halflife", TextFormat("%5.3f", halflife), &halflife, 0.0f, 4.0f);
        GuiSliderBar((Rectangle){ 125, 45, 120, 20 }, "frequency", TextFormat("%5.3f", frequency), &frequency, 0.0f, 5.0f);
        GuiSliderBar((Rectangle){ 125, 70, 120, 20 }, "goal frequency", TextFormat("%5.3f", goal_frequency), &goal_frequency, 0.0f, 5.0f);
       
        energy = spring_energy(x, v, frequency, screenHeight/2.0f, 0.0f, 0.01f);
        
        GuiSliderBar((Rectangle){ 400, 20, 120, 20 }, "energy", TextFormat("%4.1f", energy), &energy, 0.0f, 160.0f);        
        
        // Update Spring
        
        SetTargetFPS(1.0f / dt);
        
        t += dt;
        
        spring_damper_exact(x, v, g, 0.0f, frequency, halflife, dt);
        
        x_prev[0] = x;
        v_prev[0] = v;      
        t_prev[0] = t;
        g_prev[0] = g;
        
        BeginDrawing();
        
            ClearBackground(RAYWHITE);
            
            DrawCircleV((Vector2){goalOffset, g}, 5, MAROON);
            DrawCircleV((Vector2){goalOffset, x}, 5, DARKBLUE);
            
            for (int i = 0; i < HISTORY_MAX - 1; i++)
            {
                Vector2 x_start = {goalOffset - (t - t_prev[i + 0]) * timescale, x_prev[i + 0]};
                Vector2 x_stop  = {goalOffset - (t - t_prev[i + 1]) * timescale, x_prev[i + 1]};
            
                DrawLineV(x_start, x_stop, BLUE);                
                DrawCircleV(x_start, 2, BLUE);
            }
            
            for (int i = 0; i < HISTORY_MAX - 1; i++)
            {
                Vector2 g_start = {goalOffset - (t - t_prev[i + 0]) * timescale, g_prev[i + 0]};
                Vector2 g_stop  = {goalOffset - (t - t_prev[i + 1]) * timescale, g_prev[i + 1]};
                
                DrawLineV(g_start, g_stop, MAROON);                
                DrawCircleV(g_start, 2, MAROON);
            }
            
        EndDrawing();
        
    }

    CloseWindow();

    return 0;
}