double round(double x) { //thanks kccarter
  return ((x - floor(x)) >= 0.5) ? ceil(x) : floor(x);
}
void drawLine( int x1, int y1, int x2, int y2, unsigned char buf[], unsigned char color[] ) {
	int xdif = x2-x1;
	int ydif = y2-y1;
	if( abs(xdif) > abs(ydif) ) {
		if( xdif  > 0 ) {
			float slope = ydif / float(xdif);
			for(int x = 0; x < xdif; x++) {
				int y = int( round(slope*x) );
				buf[ ( x+x1 + (y+y1)*ROW ) * RGB + RED]   = color[RED];
				buf[ ( x+x1 + (y+y1)*ROW ) * RGB + GREEN] = color[GREEN];
				buf[ ( x+x1 + (y+y1)*ROW ) * RGB + BLUE]  = color[BLUE];
			}
		} else drawLine( x2, y2, x1, y1, buf ); //swap points 1 & 2
	} else { //same code but swap x and y values
		if( ydif  > 0 ) {
			float slope = xdif / float(ydif);
				for(int y = 0; y < ydif; y++) {
					int x = int( round(slope*y) );
					buf[ ( x+x1 + (y+y1)*ROW ) * RGB + RED]   = color[RED];
					buf[ ( x+x1 + (y+y1)*ROW ) * RGB + GREEN] = color[GREEN];
					buf[ ( x+x1 + (y+y1)*ROW ) * RGB + BLUE]  = color[BLUE];
				}
		} else if( xdif != ydif ) drawLine( x2, y2, x1, y1, buf ); //swap points 1 & 2
	}
}