gp off-screen ports

I'm pouring raw gp calls onto a capi:output-pane.  The result flickers because 
I'm not double-buffering.

I should be pouring the gp calls onto an off-screen port, then snapping the 
port onto the output-pane (i.e. double-buffering).  

The gp docs say that this can be done, but I haven't made the connection.  Two 
questions: (a) how do I create an off-screen port?  (b) how do I assign this 
port to an on-screen port?  

(Currently, I think that the answer to (a) is pixmaps and the answer to (b) is 
pixblt.  Is this correct?)

thanx
pt