How to grab the backbuffer *with* alpha

As it happens, I have need to do other sorts of pixel processing & don't need this in realtime, so East-Power-Soft's method works well for me. :) Thanks for the tips, though -- that's a nice r2t routine, hadn't seen it before, klepto.

ImaginaryHuman, I have no idea how to accomplish that in MaxGUI, that's why I was asking. :)

Here's what I ended up doing:

' given two identical images, one drawn on white and one drawn on black,
' return a third image that is the true color plus the alpha mask.
Function makeAlpha:TImage(img1:TImage, img2:TImage) 

	i1:TPixmap = LockImage(img1) 
	i2:TPixmap = LockImage(img2) 
	For x = 0 To ImageWidth(img1) - 1
		For y = 0 To ImageHeight(img1) - 1
			rgba = ReadPixel(i1, x, y) 
			rgba2 = ReadPixel(i2, x, y) 
			If rgba <> rgba2
				GetRGB(rgba, a, r, g, b) 
				GetRGB(rgba2, a2, r2, g2, b2) 
				newa = 255 - Abs(r - r2) 
				newrgba = GenRgb(r2, g2, b2, newa) 
				WritePixel(i1, x, y, newrgba) 
			EndIf
		Next
	Next
	Return LoadImage(i1) 

End Function

' from archives
Function GetRGB(argb:Int, a Var, r Var, g Var, b Var) 
	a=(argb Shr 24) & $ff
	r=(argb Shr 16) & $ff
	g=(argb Shr 8) & $ff
	b=argb & $ff
End Function

' from archives
Function GenRgb(RED, green, blue, Alpha = 255) 
	RGB = (Alpha Shl 24) | (RED Shl 16) | (Green Shl 8) | Blue
Return rgb
		
End Function