Circle in & circle out effect

It seems that writing the above question helped me answer it, in particular - the description of 'circle punched out of the middle of a rect' gave me an idea.

How I've achieved the effect is quite simple in the end; I make a masked image with a circle punched out of the middle, draw this image over the everything (scaled) and then draw rects on all sides of it - I've included the code for anyone that's interested.

' circle mask effect

Graphics 640,480,0
AutoMidHandle True
'create the mask image
Local timask=CreateImage(640,480,1,MASKEDIMAGE | DYNAMICIMAGE | FILTEREDIMAGE)
'set mask color to white
SetMaskColor 255,255,255
'draw white circle on black b/g
SetColor 255,255,255
DrawOval 0,0,640,480
'grab background into timask
GrabImage timask,0,0

Local done:Int=False
Local sc:Float=2

Repeat
	Cls
	For a=1 To 5000
		SetColor Rand(1,255),Rand(1,255),Rand(1,255)
		Plot Rand(1,640),Rand(1,480)
	Next

		'reduce scale of mask
	sc=sc-.01

	'draw boxes on either side of circle mask
	SetScale 1,1
	SetColor 0,0,0
	DrawRect 0,0,640,ImageHeight(timask)/2-(ImageHeight(timask)/2*sc)
	DrawRect 0,ImageHeight(timask)/2+(ImageHeight(timask)/2*sc),640,480
	DrawRect 0,0,ImageWidth(timask)/2-(ImageWidth(timask)/2*sc),480
	DrawRect ImageWidth(timask)/2+(ImageWidth(timask)/2*sc),0,640,480
	


	'draw circle mask
	SetScale sc,sc
	SetColor 255,255,255
	DrawImage timask,ImageWidth(timask)/2,ImageHeight(timask)/2
	
	Flip
	If KeyDown(key_escape) Then done=True
Until done=True