Private Const GRID_SPACING = 120
Private m_Drawing As Boolean
Private m_X1 As Single
Private m_Y1 As Single
Private m_X2 As Single
Private m_Y2 As Single

' Snap the point to the grid.
Private Sub SnapToGrid(ByRef X As Single, ByRef Y As Single)
    X = picCanvas.ScaleLeft + GRID_SPACING * CInt((X - _
        picCanvas.ScaleLeft) / GRID_SPACING)
    Y = picCanvas.ScaleTop + GRID_SPACING * CInt((Y - _
        picCanvas.ScaleTop) / GRID_SPACING)
End Sub

' Draw the positioning grid.
Private Sub Form_Resize()
Dim X As Single
Dim Y As Single

    picCanvas.Move 0, 0, ScaleWidth, ScaleHeight

    Y = 0
    Do While Y <= picCanvas.ScaleHeight
        X = 0
        Do While X <= picCanvas.ScaleWidth
            picCanvas.PSet (X, Y)
            X = X + GRID_SPACING
        Loop
        Y = Y + GRID_SPACING
    Loop

    ' Make the image permanent.
    picCanvas.Picture = picCanvas.Image
End Sub

' Start drawing a rubberband line.
Private Sub picCanvas_MouseDown(Button As Integer, Shift As _
    Integer, X As Single, Y As Single)
    ' Erase any previous line.
    picCanvas.Cls

    ' Save the first point.
    SnapToGrid X, Y
    m_X1 = X
    m_Y1 = Y
    m_X2 = X
    m_Y2 = Y

    ' Prepare to draw in rubberband mode.
    picCanvas.DrawMode = vbInvert
    m_Drawing = True
End Sub

Private Sub picCanvas_MouseMove(Button As Integer, Shift As _
    Integer, X As Single, Y As Single)
    If Not m_Drawing Then Exit Sub

    ' Snap the new point to the grid.
    SnapToGrid X, Y
    If m_X2 = X And m_Y2 = Y Then Exit Sub

    ' Erase the previous line.
    picCanvas.Line (m_X1, m_Y1)-(m_X2, m_Y2)

    ' Update the coordinates.
    m_X2 = X
    m_Y2 = Y

    ' Draw the new line.
    picCanvas.Line (m_X1, m_Y1)-(m_X2, m_Y2)
End Sub

Private Sub picCanvas_MouseUp(Button As Integer, Shift As _
    Integer, X As Single, Y As Single)
    If Not m_Drawing Then Exit Sub
    m_Drawing = False
    picCanvas.DrawMode = vbCopyPen

    ' Redraw the last line.
    picCanvas.Line (m_X1, m_Y1)-(m_X2, m_Y2), vbRed
    picCanvas.Picture = picCanvas.Image
End Sub