c++/sfml (tetris)

#include <SFML/Graphics.hpp>
#include <time.h>
using namespace sf;

const int M = 20;
const int N = 10;

int field[M][N] = {0};

struct Point
{int x,y;
} a[4], b[4];

int figures[7][4] =
{
1,3,5,7, // I
2,4,5,7, // Z
3,5,4,6, // S
3,5,4,7, // T
2,3,5,7, // L
3,5,7,6, // J
2,3,4,5, // O
};

bool check()
{
for (int i=0;i<4;i++)
if (a.x<0 || a.x>=N || a.y>=M) return 0;
else if (field[a.y][a.x]) return 0;

return 1;
};


int main()
{
srand(time(0));

RenderWindow window(VideoMode(320, 480), "The Game!");

Texture t1,t2,t3;
t1.loadFromFile("images/tiles.png");
t2.loadFromFile("images/background.png");
t3.loadFromFile("images/frame.png");

Sprite s(t1), background(t2), frame(t3);

int dx=0; bool rotate=0; int colorNum=1;
float timer=0,delay=0.3;

Clock clock;

while (window.isOpen())
{
float time = clock.getElapsedTime().asSeconds();
clock.restart();
timer+=time;

Event e;
while (window.pollEvent(e))
{
if (e.type == Event::Closed)
window.close();

if (e.type == Event::KeyPressed)
if (e.key.code==Keyboard::Up) rotate=true;
else if (e.key.code==Keyboard::Left) dx=-1;
else if (e.key.code==Keyboard::Right) dx=1;
}

if (Keyboard::isKeyPressed(Keyboard::Down)) delay=0.05;

//// <- Move -> ///
for (int i=0;i<4;i++) { b=a; a.x+=dx; }
if (!check()) for (int i=0;i<4;i++) a=b;

//////Rotate//////
if (rotate)
{
Point p = a[1]; //center of rotation
for (int i=0;i<4;i++)
{
int x = a.y-p.y;
int y = a.x-p.x;
a.x = p.x - x;
a.y = p.y + y;
}
if (!check()) for (int i=0;i<4;i++) a=b;
}

///////Tick//////
if (timer>delay)
{
for (int i=0;i<4;i++) { b=a; a.y+=1; }

if (!check())
{
for (int i=0;i<4;i++) field[b.y][b.x]=colorNum;

colorNum=1+rand()%7;
int n=rand()%7;
for (int i=0;i<4;i++)
{
a.x = figures[n] % 2;
a.y = figures[n] / 2;
}
}

timer=0;
}

///////check lines//////////
int k=M-1;
for (int i=M-1;i>0;i--)
{
int count=0;
for (int j=0;j<N;j++)
{
if (field[j]) count++;
field[k][j]=field[j];
}
if (count<N) k--;
}

dx=0; rotate=0; delay=0.3;

/////////draw//////////
window.clear(Color::White);
window.draw(background);

for (int i=0;i<M;i++)
for (int j=0;j<N;j++)
{
if (field[j]==0) continue;
s.setTextureRect(IntRect(field[j]18,0,18,18));
s.setPosition(j18,i18);
s.move(28,31); //offset
window.draw(s);
}

for (int i=0;i<4;i++)
{
s.setTextureRect(IntRect(colorNum18,0,18,18));
s.setPosition(a.x18,a.y18);
s.move(28,31); //offset
window.draw(s);
}

window.draw(frame);
window.display();
}

return 0;
}