Bresenham's line algorithm

Sub Draw_Line(x1,y1,x2,y2)
length = x2-x1
m = (y2-y1)/(x2-x1)
y = y1
For i = 0 To length
Plot(x1+i,Int(y))
y = y + m
Next i
End Sub

Sub BresenhamLine(x0, y0, x1, y1)
  steep = False
  If Abs(y1 - y0) > Abs(x1 - x0) Then
    steep = True
    'swap(x0, y0)
    x = x0 : x0 = y0 : y0 = x      
    'swap(x1, y1)
    x = x1 : x1 = y1 : y1 = x   
  End If
  If x0 > x1 Then
    'swap(x0, x1)
    x = x0 : x0 = x1 : x1 = x            
    'swap(y0, y1)
    x =y0 : y0 = y1 : y1 = x
  End If
  deltax = Int(x1 - x0)
  deltay = Int(Abs(y1 - y0))
  error = Int(deltax / 2)
  y = y0
  If y0 < y1 Then
    ystep = 1
  Else
    ystep = -1
  End If
  For x = x0 To x1
    If steep Then plot(y,x) Else plot(x,y)
    error = error - deltay
    If error < 0 Then
      y = y + ystep
      error = error + deltax
    End If
  Next
End Sub