Saving CAPI Port to PNG

If I draw rectangles, lines, text, and etc. to a CAPI port which  
displays nicely on screen, is there a way for me to capture that  
drawing and save it to a PNG file on disk?

Is there an automated way built in to CAPI?

If there is not, then is there a way for me to access the pixel  
information of the PORT, so I can manually write it to PNG myself.

Thank you,

Dr. Atip Asvanund