Advent of Code Day 9 Visualization

visual.c

#include <stdio.h>
#include <stdlib.h>
#include <SDL2/SDL.h>

#define TARGET_MS 20
#define SEGMENT_SIZE 3

static SDL_Renderer *init_sdl(void)
{
    if (SDL_Init(SDL_INIT_VIDEO) != 0) {
        fprintf(stderr, "SDL_Init failed\n");
        exit(-1);
    }
    SDL_Window *window = SDL_CreateWindow("AOC Day 9 Part 2", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, 1280, 720, 0);
    if (window == NULL) {
        fprintf(stderr, "SDL_CreateWindow failed: %s\n", SDL_GetError());
        exit(-1);
    }
    SDL_Renderer *renderer = SDL_CreateRenderer(window, -1, 0);
    if (renderer == NULL) {
        fprintf(stderr, "SDL_CreateRenderer failed: %s\n", SDL_GetError());
        exit(-1);
    }
    return renderer;
}

static void update_rope(SDL_Rect *rope, FILE *input)
{
    char direction;
    int steps;
    SDL_Point move;
    if (fscanf(input, " %c %d", &direction, &steps) == 2) {
        switch (direction) {
            case 'R':
                move.x = SEGMENT_SIZE;
                move.y = 0;
                break;
            case 'L':
                move.x = -SEGMENT_SIZE;
                move.y = 0;
                break;
            case 'U':
                move.x = 0;
                move.y = -SEGMENT_SIZE;
                break;
            case 'D':
                move.x = 0;
                move.y = SEGMENT_SIZE;
                break;
            default:
                fprintf(stderr, "Invalid input\n");
                exit(-1);
        }
        for (int i = 0; i < steps; i++) {
            rope[0].x += move.x;
            rope[0].y += move.y;
            for (int j = 1; j < 10; j++) {
                SDL_Rect *head = rope + (j - 1);
                SDL_Rect *tail = rope + j;
                if (tail->x != head->x && tail->y != head->y) {
                    if (abs(head->x - tail->x) > SEGMENT_SIZE || abs(head->y - tail->y) > SEGMENT_SIZE) {
                        if (head->x > tail->x) {
                            tail->x += SEGMENT_SIZE;
                        } else {
                            tail->x -= SEGMENT_SIZE;
                        }
                        if (head->y > tail->y) {
                            tail->y += SEGMENT_SIZE;
                        } else {
                            tail->y -= SEGMENT_SIZE;
                        }
                    }
                } else if (tail->x != head->x) {
                    if (abs(head->x - tail->x) > SEGMENT_SIZE) {
                        if (head->x > tail->x) {
                            tail->x += SEGMENT_SIZE;
                        } else {
                            tail->x -= SEGMENT_SIZE;
                        }
                    }
                } else if (tail->y != head->y) {
                    if (abs(head->y - tail->y) > SEGMENT_SIZE) {
                        if (head->y > tail->y) {
                            tail->y += SEGMENT_SIZE;
                        } else {
                            tail->y -= SEGMENT_SIZE;
                        }
                    }
                }
            }
        }
    }
}

int main(void)
{
    FILE *input = fopen("input", "r");
    if (input == NULL) {
        perror("fopen");
        return -1;
    }
    SDL_Renderer *renderer = init_sdl();
    SDL_Rect rope[10];
    for (int i = 0; i < 10; i++) {
        rope[i].x = 640;
        rope[i].y = 360;
        rope[i].w = SEGMENT_SIZE;
        rope[i].h = SEGMENT_SIZE;
    }
    Uint32 last_rendered = SDL_GetTicks();
    while (1) {
        SDL_Event event;
        while (SDL_PollEvent(&event)) {
            switch (event.type) {
                case SDL_QUIT:
                    return 0;
            }
        }
        update_rope(rope, input);
        SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);
        SDL_RenderClear(renderer);
        SDL_SetRenderDrawColor(renderer, 255, 0 ,0, 255);
        SDL_RenderFillRects(renderer, rope, 10);
        SDL_RenderPresent(renderer);
        Uint32 cur_ticks = SDL_GetTicks();
        Uint32 elapsed = cur_ticks - last_rendered;
        last_rendered = cur_ticks;
        if (elapsed < TARGET_MS) {
            Uint32 sleep_time = TARGET_MS - elapsed;
            SDL_Delay(sleep_time);
            last_rendered = SDL_GetTicks();
        }
    }
    return 0;
}