Example of Turtle Graphics Library for Excel VBA by using GDI32 Instructions

1. Copy the source program of graphics drawing library by GDI32 instructions and paste to Module 2.
2. Insert a user form. The size of the user form should be larger than Viewport.
3. Fill in the procedure for displaying the form on the workbook

Private Sub Workbook_Open()
   UserForm1.Show 
 End Sub

4. Insert buttons into Form
5. Write a CALL statement for displaying turtle graphics in the CommandButton1_Click procedure.

Private Sub CommandButton1_Click()
' Draw polygons
    TurtleTest01
End Sub

Private Sub CommandButton2_Click()
' Draw Spirals
    TurtleTest02
End Sub

Private Sub CommandButton3_Click()
' Koch curve
    DrawKochCurve
End Sub

Private Sub CommandButton4_Click()
' Tree Diagram
    DrawTree
End Sub

Private Sub CommandButton5_Click()
  SetViewPort 0, 0, 699, 629
  gClear
End Sub

6. Fill in Module 1 with procedures to obtain device context and display turtle graphics.

Option Explicit
 
Sub TurtleTest01()
' Get device context handle
    monhdc = GetForegroundWindow()
    myhdc = GetDC(monhdc)
    If myhdc = 0 Then Exit Sub

Dim i, j, side

InitializeTurtleGraphics
side = 100
       
For i = 3 To 9
    For j = 1 To i
        TGMoveL side
        TGTurn 360 / i
      Debug.Print gTGCurrentX, gTGCurrentY
    Next j
Next i

End Sub

Sub TurtleTest02()
' Get device context handle
    monhdc = GetForegroundWindow()
    myhdc = GetDC(monhdc)
    If myhdc = 0 Then Exit Sub

Dim length, angle, d
       
InitializeTurtleGraphics

    length = 300
    angle = 89
    d = 2
    TGSetPoint 600, 0
           
    Do While length > d
        TGMoveL length
        TGTurn angle
        length = length - d
    Loop
    
End Sub
   
Sub DrawKochCurve()
' Get device context handle
    monhdc = GetForegroundWindow()
    myhdc = GetDC(monhdc)
    If myhdc = 0 Then Exit Sub

    Dim i, length, n

    n = 4       ' Koch Dimension
    length = 5      ' ０-th length

    InitializeTurtleGraphics
       
    For i = 1 To 3
         Koch n, length
         TGTurn -120
    Next i

End Sub

Sub Koch(n, length)

    If n = 0 Then
        TGMoveL length
    Else
        Koch n - 1, length
        TGTurn 60
        Koch n - 1, length
        TGTurn -120
        Koch n - 1, length
        TGTurn 60
        Koch n - 1, length
    End If
    
End Sub

Sub DrawTree()
' Get device context handle
    monhdc = GetForegroundWindow()
    myhdc = GetDC(monhdc)
    If myhdc = 0 Then Exit Sub

    Dim myLength, myTurn, myRatio

    myLength = 200      ' 0-th branch length
    myTurn = 60         ' Angle of bending
    myRatio = 0.6       ' Ratio of Branch length
       
    InitializeTurtleGraphics
    
    TreeAll myLength, myTurn, myRatio

End Sub

Sub TreeAll(myLength, myTurn, myRatio)

    If myLength < 5 Then Exit Sub
    
    TGMoveL myLength, vbGreen
    TGTurn -myTurn
   
    TreeAll myLength * myRatio, myTurn, myRatio
    
    TGTurn myTurn
    TGTurn myTurn
    
    TreeAll myLength * myRatio, myTurn, myRatio
    TGTurn -myTurn
    
    TGMoveL -myLength, vbGreen
    
End Sub