Mouse pointer moving in 3D plane?

Here's some code I wrote based on a function from the Code Archives:

; -----------------------------------------------------------------------------
; Positions an entity in 3D from given 2D coordinates
Function PositionEntityFrom2D(usecam,entity,x2d#,y2d#,height#=0,camZoom#=1)
	gw=GraphicsWidth()
	gh=GraphicsHeight()
	x#=-((gw/2)-x2d)
	y#=(gh/2)-y2d
	parent=GetParent(entity)
	EntityParent entity,usecam
	z#=Abs(EntityZ(entity))
	div#=(gw/(2/camzoom))/z
	x=x/div
	y=y/div
	
;z distance determined by a straight line from camera, through xyz coordinates, to height
	TFormPoint x,y,z,usecam,0
	y3d#=height
	x3d#=TFormedX()
	z3d#=TFormedZ()
	EntityParent entity,parent
	PositionEntity entity,x3d,y3d,z3d
End Function
;-----------------------------------------------------------------------------

This function is to place an object, but it's easy to modify to just return the coordinates in 3D space. As for clicking on 2D buttons also, just ignore these 3D coordinates when the mouse pointer is over buttons and do things the normal way.