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#include <stdio.h>
#include <math.h>
#include "display.h"
#define W 1600
#define H 900
#define FPS 1000
#define SCALE 1000
#define SWING_SCALE 15
#define RFPS 1/FPS
#define PI 3.141592654
const float s = (PI/180 * 25); // rad
const float l = 0.5 * SCALE; // m
const int m = 7; // kg
const float g = -9.81f * SCALE; // m/s^2
float t;
float v;
float a;
float secs = 0.0f;
int swings = 2 * SWING_SCALE;
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()
{
float old_t = t;
a = (g/l) * sinf(t);
v += a * RFPS;
t += v * RFPS;
if(has_reached_starting_amp(old_t)) {
puts("new swing");
swings += 1;
}
if(swings >= 2 * SWING_SCALE) {
printf("period: %f\n", secs/SWING_SCALE);
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(void)
{
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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