Microsoft Small Basic

Program Listing:

'Fractal.sb modified to debug and trap some of the spurious pixels seen.
GraphicsWindow.BackgroundColor = "Black"

x = 100
y = 100
oldx = 150
oldy = 1000

'For i = 1 To 100000
For i = 1 To 100000
  r = Math.GetRandomNumber(3)
  ' r determines whether the top, bottom left or bottom right sub-triangle
  ' of the overall triangle is selected. I have used the value of r to change
  ' the pixel colour to determine this fact.
  ' You will probably need to stretch the window to see the red and blue pixels.
  'line goes from 30,1000 to 150,30
  'gradient = (30 - 1000) / (150 - 30) = - 970 / 120 = -97 / 12
  'origin = 30,1000
  'y = -97/12 * x + 1242.5 from y=mx+c knowing two co-ordinates
  'x = 30, y = 1000 and x = 150, y = 30
  ux = 150
  uy = 30
  If (r = 1) then
    ux = 30
    uy = 1000
  EndIf

  If (r = 2) Then
    ux = 1000
    uy = 1000
  EndIf

  x = (x + ux) / 2
  y = (y + uy) / 2
  If x < oldx Then
    oldx = x
' TextWindow.WriteLine("oldx = " + oldx)
  EndIf
  If y < oldy Then
    oldy = y
' TextWindow.WriteLine("oldy = " + oldy)
  EndIf

  If r=1 Then
    GraphicsWindow.SetPixel(x,y,"red")
' TextWindow.WriteLine("red pixel")
  EndIf
  If r=2 Then
    GraphicsWindow.SetPixel(x,y,"Blue")
  EndIf
  If r=3 Then
    testy = (x * -97/12) + 1242.5
    If testy > y Then
      ' Trap a pixel to the left of the large green triangle
      ' Does not trap any other stray pixels.
      TextWindow.Write("x = " + x)
      TextWindow.Write(" y = " + y)
      TextWindow.WriteLine(" testy = " + testy)
    EndIf
    GraphicsWindow.SetPixel(x,y,"LightGreen")
  EndIf
EndFor