AoC18/day10p1/main.c

#include <stdio.h>
#include <limits.h>

#include <glib.h>

struct light {
    int x;
    int y;
    int velx;
    int vely;
};

struct rect {
    int x;
    int y;
    int w;
    int h;
};

struct light *parse_lights(const char *fname, unsigned *len)
{
    FILE *f = fopen(fname, "r");
    if (!f) {
        perror(fname);
        return NULL;
    }

    GArray *array = g_array_new(FALSE, TRUE, sizeof(struct light));

    char *line = NULL;
    size_t line_len = 0;
    while (getline(&line, &line_len, f) != -1) {
        struct light light;
        sscanf(line, "position=<%d, %d> velocity=<%d, %d>",
                &light.x, &light.y, &light.velx, &light.vely);
        g_array_append_val(array, light);
    }

    *len = array->len;

    free(line);
    fclose(f);
    return (struct light *)g_array_free(array, FALSE);
}

struct rect get_frame(struct light *lights, const unsigned lights_len)
{
    struct rect res = {0};

    if (!lights_len) return res;

    res.x = lights->x;
    res.y = lights->y;
    int xmax = res.x;
    int ymax = res.y;

    for (struct light *light = lights + 1; light < lights + lights_len; light++) {
        if (light->x < res.x) res.x = light->x;
        if (light->y < res.y) res.y = light->y;
        if (light->x > xmax) xmax = light->x;
        if (light->y > ymax) ymax = light->y;
    }

    res.w = xmax - res.x + 1;
    res.h = ymax - res.y + 1;

    return res;
}

void advance_frame(struct light *lights, const unsigned lights_len)
{
    for (struct light *light = lights; light < lights + lights_len; light++) {
        light->x += light->velx;
        light->y += light->vely;
    }
}

int check_limit(const struct rect limit, struct light *lights,
                const unsigned lights_len)
{
    for (struct light *light = lights; light < lights + lights_len; light++) {
        if (light->x < limit.x) return 1;
        if (light->y < limit.y) return 1;
        if (light->x > limit.x + limit.w) return 1;
        if (light->y > limit.y + limit.h) return 1;
    }
    return 0;
}

int make_bitmap(const char *fname, const struct rect frame,
                struct light *lights, const unsigned lights_len)
{
    int bitmap_width = frame.w / CHAR_BIT;
    if (frame.w % CHAR_BIT != 0) bitmap_width++;

    size_t bitmap_size = frame.h * bitmap_width;
    char (*bitmap)[bitmap_width] = calloc(1, bitmap_size);
    if (!bitmap) {
        perror("calloc");
        return 1;
    }

    for (struct light *light = lights; light < lights + lights_len; light++) {
        if (light->x < frame.x) continue;
        if (light->y < frame.y) continue;
        if (light->x > frame.x + frame.w) continue;
        if (light->y > frame.y + frame.h) continue;

        int bitmap_x = light->x - frame.x;
        int bitmap_y = light->y - frame.y;

        bitmap[bitmap_y][bitmap_x / CHAR_BIT] |= 1 << (CHAR_BIT - bitmap_x % CHAR_BIT - 1);
    }

    FILE *f = fopen(fname, "w");
    if (!f) {
        perror(fname);
        free(bitmap);
        return 1;
    }

    fprintf(f, "P4\n%d %d\n", frame.w, frame.h);
    fwrite(bitmap, bitmap_size, 1, f);

    free(bitmap);
    fclose(f);
    return 0;
}

#define REASONABLE_HEIGHT 100

int main()
{
    unsigned lights_len;
    struct light *lights = parse_lights("input", &lights_len);
    if (!lights) return 1;

    struct rect frame;

    while (1) {
        frame = get_frame(lights, lights_len);
        if (frame.h <= REASONABLE_HEIGHT) break;
        advance_frame(lights, lights_len);
    }

    GString *fname = g_string_new(NULL);
    unsigned frame_id = 0;
    while (check_limit(frame, lights, lights_len) == 0) {
        g_string_printf(fname, "out/frame%03d.pbm", frame_id++);
        if (make_bitmap(fname->str, frame, lights, lights_len)) break;
        advance_frame(lights, lights_len);
    }

    g_string_free(fname, TRUE);
    free(lights);
    return 0;
}