Определение выпуклой оболочки по методу Джарвиса

Dim n, m(), ob()
 
 
 
Private Sub Command1_Click()
Picture1.Cls
n = Val(Text1.Text)
If n < 3 Then n = 3
Text1.Text = n
ReDim m(2, n), ob(n, 2)
 For i = 1 To n
  m(1, i) = Int(Rnd * 180) - 90
  m(2, i) = Int(Rnd * 180) - 90
  Picture1.Circle (m(1, i), m(2, i)), 3
Next i
   
Call d
End Sub
 
 
Sub d() 'процедура построения оболочки
 
Picture1.Line (-100, 0)-(100, 0)
Picture1.Line (0, -100)-(0, 100)
 
First = 1
  For i = 2 To n
    If (m(1, i) < m(1, First)) Or (m(1, i) = m(1, First)) And (m(2, i) < m(2, First)) Then
       First = i
     End If
  Next i
  M_ind = 0: Cur = First
 
 
 
Do
   M_ind = M_ind + 1: Min = Cur
   
  For i = n To 1 Step -1
  If (m(1, i) <> m(1, Cur)) Or (m(2, i) <> m(2, Cur)) Then
       z = St(m(1, Cur), m(1, i), m(1, Min), m(2, Cur), m(2, i), m(2, Min))
       z1 = L(m(1, Min), m(1, Cur), m(2, Min), m(2, Cur))
       z2 = L(m(1, i), m(1, Cur), m(2, i), m(2, Cur))
    If Min = Cur Or z > 0 Or (z = 0 And z2 - z1 > 0) Then
       Min = i
       ob(M_ind, 1) = m(1, i)
       ob(M_ind, 2) = m(2, i)
    End If
  End If
  Next i
  Cur = Min
Loop Until Cur = First Or M_ind = n
 
 
For i = 2 To M_ind
  Picture1.Line (ob(i, 1), ob(i, 2))-(ob(i - 1, 1), ob(i - 1, 2))
Next i
 Picture1.Line (ob(M_ind, 1), ob(M_ind, 2))-(ob(1, 1), ob(1, 2))
End Sub
 
Function St(xa, xb, xc, ya, yb, yc) 'скалярное произведение
St = (xb - xa) * (yc - ya) - (yb - ya) * (xc - xa)
End Function
Function L(xa, xb, ya, yb) 'расстояние
L = Sqr((xb - xa) ^ 2 + (yb - ya) ^ 2)
End Function
 
Private Sub Form_Load()
Picture1.AutoRedraw = True
Picture1.Width = Picture1.Height
Picture1.Scale (-100, 100)-(100, -100)
 
End Sub