Draw tiles using line tool

[yuripourre]

Let user draw more tiles per click

Hint: Use Bresenham Algorithm as in http://eugen.dedu.free.fr/projects/bresenham/

// use Bresenham-like algorithm to print a line from (y1,x1) to (y2,x2)
// The difference with Bresenham is that ALL the points of the line are
//   printed, not only one per x coordinate.
// Principles of the Bresenham's algorithm (heavily modified) were taken from:
//   http://www.intranet.ca/~sshah/waste/art7.html
void useVisionLine (int y1, int x1, int y2, int x2)
{
  int i;               // loop counter
  int ystep, xstep;    // the step on y and x axis
  int error;           // the error accumulated during the increment
  int errorprev;       // *vision the previous value of the error variable
  int y = y1, x = x1;  // the line points
  int ddy, ddx;        // compulsory variables: the double values of dy and dx
  int dx = x2 - x1; //(dx/=tile.w)
  int dy = y2 - y1; //(dy/=tile.h)
  POINT (x1, y1);  // first point
  // NB the last point can't be here, because of its previous point (which has to be verified)
  if (dy < 0) {
    ystep = -1;
    dy = -dy;
  } else {
    ystep = 1;
  }
  if (dx < 0) {
    xstep = -1;
    dx = -dx;
  } else {
    xstep = 1;
  }

  ddy = 2 * dy;  // work with double values for full precision
  ddx = 2 * dx;
  if (ddx >= ddy){  // first octant (0 <= slope <= 1)
    // compulsory initialization (even for errorprev, needed when dx==dy)
    errorprev = error = dx;  // start in the middle of the square
    for (i=0 ; i < dx ; i++){  // do not use the first point (already done)
      x += xstep;
      error += ddy;
      if (error > ddx){  // increment y if AFTER the middle ( > )
        y += ystep;
        error -= ddx;
        // three cases (octant == right->right-top for directions below):
        if (error + errorprev < ddx)  // bottom square also
          POINT (x, y-ystep);
        else if (error + errorprev > ddx)  // left square also
          POINT (x-xstep, y);
        else{  // corner: bottom and left squares also
          POINT (x, y-ystep);
          POINT (x-xstep, y);
        }
      }
      POINT (x, y);
      errorprev = error;
    }
  }else{  // the same as above
    errorprev = error = dy;
    for (i=0 ; i < dy ; i++){
      y += ystep;
      error += ddx;
      if (error > ddy){
        x += xstep;
        error -= ddy;
        if (error + errorprev < ddy)
          POINT (x-xstep, y);
        else if (error + errorprev > ddy)
          POINT (x, y-ystep);
        else{
          POINT (x-xstep, y);
          POINT (x, y-ystep);
        }
      }
      POINT (x, y);
      errorprev = error;
    }
  }
  // assert ((y == y2) && (x == x2));  // the last point (y2,x2) has to be the same with the last point of the algorithm
}