lineOnGrid

void mousePressed()
{
  mouseOldCordX = mouseX/cellSize;
  mouseOldCordY = mouseY/cellSize;
}

void mouseReleased()
{
  mouseNewCordX = mouseX/cellSize;
  mouseNewCordY = mouseY/cellSize;

  lineDrawing();
}

void lineDrawing()
{
  int deltaX = mouseNewCordX - mouseOldCordX, deltaY = mouseNewCordY - mouseOldCordY;
  int gradient = deltaY + deltaY, error = gradient - deltaX;

  if (abs(deltaY) < abs(deltaX))
  {
    if (mouseOldCordX > mouseNewCordX)
    {
      plotLineLow(mouseOldCordX, mouseOldCordY, deltaX, deltaY, gradient, error);
    } else
    {
      plotLineLow(mouseNewCordX, mouseNewCordY, deltaX, deltaY, gradient, error);
    }
  } else
  {
    if (mouseOldCordY > mouseNewCordY)
    {
      plotLineHigh(mouseOldCordX, mouseOldCordY, deltaX, deltaY, gradient, error);
    } else
    {
      plotLineHigh(mouseNewCordX, mouseNewCordY, deltaX, deltaY, gradient, error);
    }
  }
}

void plotLineLow(int x0, int y0, int deltaX, int deltaY, int gradient, int error)
{
  int yIncrease = 1;

  if (deltaY < 0)
  {
    yIncrease = -1;
    deltaY = -deltaY;
  }

  for (int x = mouseOldCordX; x <= mouseNewCordX; x += 1)
  {

    world[x][y0].state = selectedState;

    error += gradient;

    if (error >= 0)
    {
      y0 += yIncrease;
      error -= (deltaX + deltaX);
    }
  }
}

void plotLineHigh(int x0, int y0, int deltaX, int deltaY, int gradient, int error)
{
  int xIncrease = 1;

  if (deltaX < 0)
  {
    xIncrease = -1;
    deltaX = -deltaX;
  }

  for (int y = mouseOldCordY; y <= mouseNewCordY; y += 1)
  {

    world[x0][y].state = selectedState;

    error += gradient;

    if (error >= 0)
    {
      x0 += xIncrease;
      error -= (deltaY + deltaY);
    }
  }
}