[sneak preview] B4XTurtle - library for teaching kids programming

Sub Process_Globals
    Private MainForm As Form
    Private Turtle1 As B4XTurtle
    Private xui As XUI
End Sub

Sub AppStart (Form1 As Form, Args() As String)
    MainForm = Form1
    MainForm.RootPane.LoadLayout("1")
    MainForm.Show
    TurtleStart
End Sub

Sub TurtleStart
    Turtle1.X = 20
    Turtle1.Y = 50
    Turtle1.Angle = 90
    Turtle1.MoveForward(230)
    HalfCircle
    HalfCircle
    Turtle1.Y = 50
    Turtle1.X = 140
    Turtle1.Angle = 90
    Turtle1.MoveForward(120)
    Turtle1.TurnLeft(90)
    Turtle1.MoveForward(100)
    Turtle1.X = 200
    Turtle1.Y = 50
    Turtle1.Angle = 90
    Turtle1.MoveForward(220)
    Turtle1.Y = 50
    Turtle1.X = 250
    Turtle1.Angle = 60
    Turtle1.MoveForward(250)
    Turtle1.Y = 50
    Turtle1.Angle = 120
    Turtle1.MoveForward(250)
    Turtle1.PenColor = xui.Color_Blue
    For i = 1 To 2000
        Turtle1.MoveForward(2 - i / 1000)
        Turtle1.TurnLeft(1)
    Next
End Sub

Sub HalfCircle
    Turtle1.Angle = 0
    Turtle1.MoveForward(20)
    For i = 1 To 180
        Turtle1.MoveForward(1)
        Turtle1.TurnLeft(1)
    Next
    Turtle1.MoveForward(20)
End Sub

Sub Turtle1_Start
    Turtle1.SetPenSize(1).SetSpeedFactor(30)
    Turtle1.SetX(Turtle1.Width / 2).SetY(Turtle1.Height - 100)
    Turtle1.TurnLeft(90)
    Tree(13, 100)
End Sub

Sub Tree (Level As Int, Size As Float)
    If Level > 0 Then
        Turtle1.SetPenSize(Level / 2)
        Turtle1.MoveForward(Size).TurnLeft(10)
        Tree(Level - 1, Size * 0.8)
        Turtle1.TurnRight(40)
        Tree(Level - 1, Size * 0.8)
        Turtle1.TurnLeft(30)
        Turtle1.PenUp.MoveBackward(Size).PenDown
    End If
End Sub

Sub Button1_Click
    Turtle1.ClearScreen.MoveHome.SetX(Turtle1.Width / 2 - 100)
    For i = 1 To 3
        Turtle1.SetPenSize(4).SetPenColor(Rnd(xui.Color_Black, xui.Color_White))
        KochCurve(5, 400)
        Turtle1.TurnLeft(120)
    Next
End Sub

Sub KochCurve (Level As Int, Size As Float)
    If Level < 1 Then 
        Turtle1.MoveForward(Size)
        Return
    End If
    KochCurve(Level - 1, Size / 3)
    Turtle1.TurnLeft(60)
    KochCurve(Level - 1, Size / 3)
    Turtle1.TurnRight(120)
    KochCurve(Level - 1, Size / 3)
    Turtle1.TurnLeft(60)
    KochCurve(Level - 1, Size / 3)
End Sub

Sub Button1_Click
    Turtle1.ClearScreen.MoveHome
    Dim NumberOfEdges As Int = TextField1.Text
    For i = 1 To NumberOfEdges
        Turtle1.SetPenColor(Rnd(xui.Color_Black, xui.Color_White))
        Turtle1.MoveForward(100)
        Turtle1.TurnLeft(360 / NumberOfEdges)
    Next
End Sub