Sample of the Week, II

This week's featured sample comes from Jeff Sidlosky. It is a star field simulation - you know the one where it appears like you're moving fast through space, with stars whizzing past you.

' Star-field simulation
Initialize()   
Main()   
  
Sub Initialize   
    GraphicsWindow.Title = "Super Star Field!"  
    GraphicsWindow.Width = 640   
    GraphicsWindow.Height = 480   
    GraphicsWindow.BackgroundColor = "black"  
    GraphicsWindow.PenWidth = 0   
    GraphicsWindow.Show()   
       
    num_stars = 200   
       
    For index = 0 To num_stars   
        NewStar()   
    EndFor   
EndSub   
  
Sub NewStar   
    Array.SetValue("star_x", index, Math.GetRandomNumber(100) - 50)   
    Array.SetValue("star_y", index, Math.GetRandomNumber(100) - 50)   
       
    ' Pick a random z depth   
    z = (Math.GetRandomNumber(50) / 100) + 0.50   
       
    Array.SetValue("star_z", index, z)   
       
    ' Start with a dark color and save our shape   
    GraphicsWindow.BrushColor = "DimGray"  
    Array.SetValue("star_shape", index, GraphicsWindow.AddRectangle(2, 2))   
    Array.SetValue("star_color", index, 0)   
EndSub   
  
Sub Update   
    For index = 0 To num_stars   
        z = Array.GetValue("star_z", index)         
        x = (Array.GetValue("star_x", index) / z) + 320   
        y = (Array.GetValue("star_y", index) / z) + 240   
        shape = Array.GetValue("star_shape", index)   
           
        ' Next z position   
        z = z - 0.02   
           
        If(x < 0 Or x > 639 Or y < 0 Or y > 479 Or z <= 0) Then  
            GraphicsWindow.RemoveShape(shape)   
            NewStar()   
        Else  
            ' Check if we should make the star brighter   
            If(z < 0.4) Then  
                If(Array.GetValue("star_color", index) = 0) Then  
                    GraphicsWindow.BrushColor = "White"  
                    GraphicsWindow.RemoveShape(shape)   
                    shape = GraphicsWindow.AddRectangle(2, 2)   
                    Array.SetValue("star_shape", index, shape)    
                    Array.SetValue("star_color", index, 1)   
                EndIf   
            EndIf   
               
            GraphicsWindow.MoveShape(shape, x, y)   
                
            Array.SetValue("star_z", index, z)           
        EndIf       
    EndFor   
EndSub   
  
Sub Main   
    ' Run forever   
    While(1 = 1)   
        Update()   
    EndWhile   
EndSub

And here's the screenshot! The picture really doesn't do justice. Try this program on your copy of Small Basic to experience the real deal.