snake.cc

// unixoid:
//   g++ -fno-ident -Wall -std=c++11 -s -O2 -o snake snake.cc $(sdl2-config --libs)
// win:
//   windres snake.rc -O coff snake.res && g++ -fno-ident -Wall -std=c++11 -s -O2 -o snake snake.cc snake.res -static $(sdl2-config --static-libs)

#include <SDL2/SDL.h>

const auto WIDTH = 320, HEIGHT = 240, BLOCK = 16;
constexpr auto MAX_SEGS = ((WIDTH / BLOCK) * (HEIGHT / BLOCK));
constexpr auto MAX_DOTS = (MAX_SEGS / 100);

template <typename T, unsigned N>
struct Array {
	T v[N];
	unsigned n;
	inline T& operator[](unsigned i) { return v[i]; }
	void del(unsigned i)
	{
		if (i == n - 1) {
			n--;
			return;
		}
		for (; i < (n - 1); i++) {
			v[i] = v[i + 1];
		}
		n--;
	}
};

struct Vec2 {
	float x, y;
	inline Vec2 operator+(Vec2 o) { return (Vec2){ x + o.x, y + o.y }; }
	inline Vec2 operator*(float f) { return (Vec2){ x * f, y * f }; }
	inline bool operator==(Vec2 o) { return x == o.x && y == o.y; }
};

struct Snake {
	Array<Vec2, MAX_SEGS> segs;
	Vec2 dir, ldir;
	bool addseg;
	inline void reset()
	{
		dir = ldir = (Vec2){ -1, 0 };
		segs[0] = (Vec2){ ((WIDTH / 2) / BLOCK) * BLOCK,
			((HEIGHT / 2) / BLOCK) * BLOCK };
		segs.n = 1;
		addseg = false;
	}
	inline Vec2& head() { return segs[0]; }
	inline Vec2& tail() { return segs[segs.n - 1]; }
	inline unsigned len() { return segs.n; }
};

int main(int argc, char** argv)
{
	SDL_Init(SDL_INIT_VIDEO);
	auto win = SDL_CreateWindow("snake", SDL_WINDOWPOS_CENTERED,
		SDL_WINDOWPOS_CENTERED, WIDTH, HEIGHT, 0);
	auto rend = SDL_CreateRenderer(
		win, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
	Array<Vec2, MAX_DOTS> dots;
	Snake snek;
	unsigned lt, ct, movt, ssegs;
	SDL_Event e;
	srand(SDL_GetTicks());
game:
	movt = 0;
	dots.n = 0;
	snek.reset();
	ssegs = 3;
	lt = SDL_GetTicks();
	for (;;) {
		ct = SDL_GetTicks();
		while (SDL_PollEvent(&e))
			if (e.type == SDL_QUIT
				|| (e.type == SDL_KEYUP
					   && e.key.keysym.scancode == SDL_SCANCODE_ESCAPE))
				goto end;
		auto kb = SDL_GetKeyboardState(NULL);
		Vec2 ndir = { 0, 0 };
		if (kb[SDL_SCANCODE_UP])
			ndir.y = -1;
		else if (kb[SDL_SCANCODE_DOWN])
			ndir.y = 1;
		if (kb[SDL_SCANCODE_LEFT])
			ndir.x = -1;
		else if (kb[SDL_SCANCODE_RIGHT])
			ndir.x = 1;
		if (!(ndir.y == snek.ldir.y * -1 || ndir.x == snek.ldir.x * -1)
			&& !(ndir.x && ndir.y))
			snek.dir = ndir;
		movt += ct - lt;
		if (movt > 120) {
			movt = 0;
			snek.ldir = snek.dir;
			if (ssegs) {
				ssegs--;
				snek.addseg = true;
			} else {
				if (dots.n < MAX_DOTS && (rand() % 6) == 0) {
					Vec2 dot
						= (Vec2){ (float)(rand() % (WIDTH / BLOCK) * BLOCK),
							  (float)(rand() % (HEIGHT / BLOCK) * BLOCK) };
					bool occ = false;
					for (unsigned i = 0; i < snek.len(); i++) {
						if (dot == snek.segs[i]) {
							occ = true;
							break;
						}
					}
					if (!occ) {
						for (unsigned i = 0; i < dots.n; i++) {
							if (dot == dots[i]) {
								occ = true;
								break;
							}
						}
						if (!occ) {
							dots[dots.n] = dot;
							dots.n++;
						}
					}
				}
			}
			auto nhead = snek.head() + (snek.dir * BLOCK);
			if (nhead.x < 0 || nhead.x >= WIDTH || nhead.y < 0
				|| nhead.y >= HEIGHT)
				goto game;
			Vec2 oldtail = snek.tail();
			for (unsigned i = snek.len() - 1; i >= 1; --i) {
				Vec2& s = snek.segs[i];
				if (nhead == s)
					goto game;
				s = snek.segs[i - 1];
			}
			snek.head() = nhead;
			if (!snek.addseg) {
				for (unsigned i = 0; i < dots.n; i++) {
					if (snek.head() == dots[i]) {
						snek.addseg = true;
						dots.del(i);
						break;
					}
				}
			}
			if (snek.addseg) {
				snek.addseg = false;
				snek.segs.n++;
				snek.tail() = oldtail;
			}
		}
		SDL_SetRenderDrawColor(rend, 0x00, 0x00, 0x00, 0xFF);
		SDL_RenderClear(rend);
		SDL_Rect r[MAX_SEGS];
		{
			for (unsigned i = 0; i < snek.len(); i++) {
				auto s = snek.segs[i];
				r[i] = (SDL_Rect){ (int)s.x, (int)s.y, BLOCK, BLOCK };
			}
			SDL_SetRenderDrawColor(rend, 0xFF, 0x44, 0x00, 0xFF);
			SDL_RenderFillRect(rend, &r[0]);
			SDL_SetRenderDrawColor(rend, 0x00, 0xFF, 0x00, 0xFF);
			SDL_RenderFillRects(rend, &r[1], snek.len() - 1);
		}
		if (dots.n) {
			for (unsigned i = 0; i < dots.n; i++) {
				auto d = dots[i];
				r[i] = (SDL_Rect){ (int)(d.x + (BLOCK / 4)),
					(int)(d.y + (BLOCK / 4)), BLOCK / 2, BLOCK / 2 };
			}
			SDL_SetRenderDrawColor(rend, 0xFF, 0x00, 0xFF, 0xFF);
			SDL_RenderFillRects(rend, r, dots.n);
		}
		SDL_RenderPresent(rend);
		lt = ct;
	}
end:
	SDL_DestroyRenderer(rend);
	SDL_DestroyWindow(win);
	SDL_Quit();
	return 0;
}