I was just looking at this topic and thought there must be an easier and quicker method to get the effect right so here is my offering...
InitSprite()
If OpenWindow(0, 0, 0, 820, 620, "Old School Decrunch Effect...", #PB_Window_SystemMenu | #PB_Window_SizeGadget | #PB_Window_ScreenCentered)
If OpenWindowedScreen(WindowID(0), 10, 10, 800, 600, #True, 10, 10, #PB_Screen_NoSynchronization) ; x, y position, width, height, autostretch
If CreateSprite(0, 800, 600) ; sprite, width, height
Repeat
MyEvent = WindowEvent()
If StartDrawing(SpriteOutput(0))
Box(0, Random(600), 800, 10, RGB((Random(255)), (Random(255)), (Random(255)))) ; Entire field x, y radius, width, height, colour
StopDrawing()
EndIf
FlipBuffers()
DisplaySprite(0, 0, Random(600))
Until MyEvent = #PB_Event_CloseWindow
EndIf
EndIf
EndIf
Ted.