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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <math.h>
#include "display.h"
#define W 800
#define H 600
#ifndef PLATFORM_WEB
#define FPS 120
#else
#define FPS 60
#endif
#define SCALE 800
#define CYCLES 5
#define RFPS 1/FPS
#define PI 3.141592654
#define g -9.81f * SCALE
float s = 25; // starting agnle
float l = 0.5; // lenght
float m = 0.01; // mass in kg
float t;
float v;
float a;
float secs = 0.0f;
int swings = 2 * CYCLES;
int has_reached_starting_amp(float old_t)
{
if(swings % 2 == 0 && t < 0) {
if(old_t < t) return 1;
} else if(swings % 2 == 1 && t > 0) {
if(old_t > t) return 1;
} return 0;
}
void update()
{
if(secs == 0.0f) {
printf("\nStarting angle: %f", s/(PI/180));
printf("\nLenght: %f", l/SCALE);
printf("\nMass: %f\n", m/SCALE);
}
float old_t = t;
a = (g/l) * sinf(t);
v += a * RFPS;
t += v * RFPS;
if(has_reached_starting_amp(old_t)) {
swings += 1;
}
if(swings >= 2 * CYCLES) {
printf("period: %f\n", secs/CYCLES);
secs = 0.0f;
swings = 0;
}
secs += (float)RFPS;
float px = sinf(t) * l;
float py = cosf(t) * l;
dspl_draw_line(px, py, 0, 0, 0);
dspl_draw_circle(px, py, m);
}
int main(int argc, char **argv)
{
if(argc != 1 && argc != 4) {
puts("Please provide either 0 or 3 arguments:\n\t1st is starting angle in degrees\n\t2nd is lenght in meters\n\t3rd is mass in kilograms");
return 1;
}
float arg_s = strtof(argv[1], NULL);
float arg_l = strtof(argv[2], NULL);
float arg_m = strtof(argv[3], NULL);
s = ((arg_s == 0.0f) ? s : arg_s) * PI/180;
l = ((arg_l == 0.0f) ? l : arg_l) * SCALE;
m = ((arg_m == 0.0f) ? m : arg_m) * SCALE;
t = s;
v = 0;
a = 0;
dspl_createinfo info = {0};
info.width = W;
info.height = H;
info.name = "Pendulum";
info.fps = FPS;
info.update_func = &update;
dspl_create(info);
dspl_start();
dspl_destroy();
return 0;
}
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