mjestecko/articles/oscillators/waveforms.c

#include <stdio.h>
#include <inttypes.h>
#include <math.h>
#include <assert.h>
#include <string.h>

#include "gifenc/gifenc.h"

#define NOTE 440
#define AUDIO_FRAME_RATE 44100
#define LENGTH (AUDIO_FRAME_RATE / NOTE)

#define WIDTH LENGTH * 4
#define HEIGHT 128

#define RED 0
#define GREEN 0
#define BLUE 255

static struct sinewave {
    float f, s, c;
} init_sinewave(float frequency, float phase, float amplitude) {
    struct sinewave r;
    r.f = 2.f * sinf((float)M_PI * frequency / (float)AUDIO_FRAME_RATE);
    r.s = amplitude * sinf(phase);
    r.c = amplitude * cosf(phase);
    return r;
}

static float pump_sinewave(struct sinewave *wave) {
    wave->s -= wave->f * wave->c;
    wave->c += wave->f * wave->s;
    return wave->s;
}

static struct sqrtwave {
  struct sinewave w;
  union {
    float f;
    uint32_t u;
  } v;
} init_sqrtwave(float frequency, float phase, float amplitude) {
    struct sqrtwave r;
  union {
    float f;
    uint32_t u;
  } v, a;
    r.w = init_sinewave(frequency, phase, 1.f);
    v.f = r.w.s;
    a.f = amplitude;
    r.v.u = (a.u & 0x7fffffff) | (v.u & 0x80000000);
    return r;
}

static float pump_sqrtwave(struct sqrtwave *wave) {
  union {
    float f;
    uint32_t u;
  } v;
    pump_sinewave(&wave->w);
    v.f = wave->w.s;
    wave->v.u = (wave->v.u & 0x7fffffff) | (v.u & 0x80000000);
    return wave->v.f;
}

static struct sawtwave {
    float v, a, i;
} init_sawtwave(float frequency, float phase, float amplitude) {
    struct sawtwave r;
    r.v = sinf(phase) * amplitude;
    r.a = amplitude;
    r.i = 2.f * frequency / AUDIO_FRAME_RATE * amplitude;
    return r;
}

static float pump_sawtwave(struct sawtwave *wave) {
    wave->v += wave->i;
    if (wave->v > wave->a)
      wave->v -= wave->a * 2.f;
    return wave->v;
}

static int absi(int v) {
    return v > 0 ? v : -v;
}

static void plot_line(uint8_t *frame, int x, int xt, int y, int yt) {
    int dx = xt - x;
    int dy = yt - y;
    int step = absi(dx) >= absi(dy) ? absi(dx) : absi(dy);
    dx /= step;
    dy /= step;
    int xc = x;
    int yc = y;
    int i = 1;
    while (i <= step) {
        frame[xc + yc * WIDTH] = 1;
        xc += dx;
        yc += dy;
        i++;
    }
}

static void generate_wave(char const *filepath, void *generator, float (*pumper)(void *)) {
  float wave[LENGTH];
  for (int i = 0; i < LENGTH; ++i) {
    wave[i] = pumper(generator);
  }
  uint8_t palette[6] = { [3] = RED, [4] = GREEN, [5] = BLUE };
  ge_GIF *g = ge_new_gif(filepath, WIDTH, HEIGHT, palette, 1, 0, 0);
  assert(g);
  for (int f = 0; f < LENGTH; ++f) {
    memset(g->frame, 0, WIDTH * HEIGHT);
    for (int i = 0; i < WIDTH; ++i) {
        int l0 = (int)((wave[(f + i) % LENGTH] + 1.0f) * 127.5f) / 2;
        int l1 = (int)((wave[(f + i + 1) % LENGTH] + 1.0f) * 127.5f) / 2;
        if (i == WIDTH - 1)
            g->frame[i + l0 * WIDTH] = 1;
        else
            plot_line(g->frame, i, i + 1, l0, l1);
    }
    ge_add_frame(g, 1);
  }
  ge_close_gif(g);
}

int main(void) {
    struct sinewave sine = init_sinewave((float)NOTE, 0.0f, 1.0f);
    generate_wave(".dynamic/sine.gif", &sine, pump_sinewave);

    struct sqrtwave sqrt = init_sqrtwave((float)NOTE, 0.0f, 1.0f);
    generate_wave(".dynamic/sqrt.gif", &sqrt, pump_sqrtwave);

    struct sawtwave sawt = init_sawtwave((float)NOTE, 0.0f, 1.0f);
    generate_wave(".dynamic/sawt.gif", &sawt, pump_sawtwave);

    return 0;
}