#include <math.h>
#include <SDL/SDL.h>
	#define PI 3.14159
	#define SWIDTH 640
	#define SHEIGHT 400
void Putpixel(SDL_Surface *screen, int x, int y, int r, int g, int b) {
	unsigned char *pixel;
	pixel = screen->pixels;
	pixel = pixel + y * SWIDTH * 4;
	pixel = pixel + x * 4;
	*pixel = b; pixel++;
	*pixel = g; pixel++;
	*pixel = r;
}
int sgn (long a) {
	if (a > 0) return +1;
		else if (a < 0) return -1;
			else return 0;
}
void Line(SDL_Surface *screen, int a, int b, int c, int d, int col) {
	long u,s,v,d1x,d1y,d2x,d2y,m,n;
	int  i;
	u   = c-a;
	v   = d-b;
	d1x = sgn(u);
	d1y = sgn(v);
	d2x = sgn(u);
	d2y = 0;
	m   = abs(u);
	n   = abs(v);
	if (m <= n) {
		d2x = 0;
		d2y = sgn(v);
		m   = abs(v);
		n   = abs(u);
	}
	s = (int)(m / 2);
	for (i = 0; i < round(m); i++) {
		Putpixel(screen, a, b, 255, 255, 255);
		s = s + n;
		if (s >= m) {
			s = s - m;
			a = a + d1x;
			b = b + d1y;
		} else {
			a = a + d2x;
			b = b + d2y;
		}
	}
}
int main(int argc, char *argv[])
{
	SDL_Init(SDL_INIT_VIDEO);
	SDL_WM_SetCaption("Rotating", NULL);
	SDL_Surface *screen = SDL_SetVideoMode(640, 400, 32, SDL_SWSURFACE);
	SDL_Event event;
	int angle = 0, i;
	while (1) {
		SDL_FillRect(screen, NULL, 0);
		SDL_PollEvent(&event);
		if (event.type == SDL_QUIT) break;
			else if (event.type == SDL_KEYDOWN)
				if (event.key.keysym.sym == SDLK_ESCAPE) break;
		Line(screen, 320, 200, -sin(angle*PI/180)*100+320, cos(angle*PI/180)*100+200, 255);
		Line(screen, 320, 200, -sin((angle+90)*PI/180)*100+320, cos((angle+90)*PI/180)*100+200, 255);
		if (angle > 360) angle = 0;
		angle = angle + 1;
		SDL_Delay(1);
		SDL_Flip(screen);
	}
	SDL_FreeSurface(screen);
	SDL_Quit();
	return 0;
}