Naives Programm:

void DrawLine(
  int x0, int y0,
  int x1, int y1,
  int color
) {

  for(int x(x0); x!=x1+1; x++) {

    const double y( y0 + (x-x0) * (y1-y0)/(x1-x0) );

    SetPixel(x, Round(y), color);

  }

}