Circle/Math Question

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Arcadenut

What I want to do is be able to constrict an objec to within a circle. Doing it inside a sqaure is easy, but I'm finding the Circle to be a bit of a challenge :-)

If anyone can help, I would greatly appreciate it!

Here is some sample code to demo what I am looking for.

Graphics 800, 600

Local cX# = 400
Local cY# = 300
Local cW# = 100
Local cH# = 100

Local x#
Local y#

Local r%

Local pX# = cX#
Local pY# = cY#

While Not KeyHit(KEY_ESCAPE)

	Cls()	
	DrawText "I want the WHITE cricle to be constricted to the inside of the Green Circle", 0,0
	DrawText "It should be able to travel smoothly around the inside of the Green Circle", 0,18
	SetColor(0,255,0)
	For r% = 0 To 360
		x# = cX# + (sin(r%) * cW)
		y# = cY# + (cos(r%) * cH)
		Plot x#, y#
	Next
	SetColor(255,255,255)
	DrawOval pX, pY, 5,5
	
	If KeyDown(KEY_LEFT) Then
		pX :- 1
	EndIf

	If KeyDown(KEY_RIGHT) Then
		pX :+ 1
	EndIf
	
	If KeyDown(KEY_UP) Then
		pY :- 1
	EndIf

	If KeyDown(KEY_DOWN) Then
		pY :+ 1
	EndIf
	
	' How do I do this...
	' IF pX on the edge of the Circle pX = the Edge of the circle
	' IF pY on the edge of the Circle pY = the Edge of the circle
	
	
	Flip()

Wend