SDL2

fractal.cpp

#include <iostream>
#include <SDL.h>
#undef main

struct Point {
  int x;
  int y; 
};

SDL_Window *window;
SDL_Renderer *renderer;

const int WIDTH = 1024;
const int HEIGHT = 768;

void change_color() {
  SDL_SetRenderDrawColor(renderer, 155 + rand(), 155 + rand(), 155 + rand(), SDL_ALPHA_OPAQUE);
}

void line(Point a, Point b) {
  change_color();
  SDL_RenderDrawLine(renderer, a.x, a.y, b.x, b.y);
}

void triangle(Point a, Point b, Point c) {
  line(a, b);
  line(b, c);
  line(a, c);
}

void fractal(Point a, Point b, Point c, int limit) {
  if (limit > 0) {
    Point _a = {
      a.x + (b.x - a.x) / 2,
      a.y - (a.y - b.y) / 2
    };
    Point _b = {
      b.x + (c.x - b.x) / 2,
      b.y - (b.y - c.y) / 2
    };
    Point _c = {
      a.x + (c.x - a.x) / 2,
      a.y
    };
    fractal(a, _a, _c, limit - 1);
    fractal(_a, b, _b, limit - 1);
    fractal(_c, _b, c, limit - 1);
  } else {
    triangle(a, b, c);
  }
}

int main() {
  bool done = false;
  SDL_Event event;

  SDL_Init(SDL_INIT_EVERYTHING);
  window = SDL_CreateWindow(
    "Fractals",
    SDL_WINDOWPOS_CENTERED,
    SDL_WINDOWPOS_CENTERED,
    WIDTH,
    HEIGHT,
    SDL_WINDOW_SHOWN
  );
  renderer = SDL_CreateRenderer(window, -1, 0);  

  Point a = { 0, HEIGHT };
  Point b = { WIDTH / 2, 0 };
  Point c = { WIDTH, HEIGHT };

  fractal(a, b, c, 6);
  
  SDL_RenderPresent(renderer);

  while (!done) {
    while (SDL_PollEvent(&event)) {
      if (event.type == SDL_KEYDOWN) {
        done = true;
      }
    }
  }   

  SDL_DestroyRenderer(renderer);
  SDL_DestroyWindow(window);
  SDL_Quit();

	return 0;
}