how Gtk::DrawingArea multithread drawing video and draw text, line , or rect...

["chan thexin" <thexinchan gmail com>]

hello
 i have a newby in gtkmm,and pool english,i want to write a app that can draw video in background ,and draw text on video with foreground,

 i had show video with gtk+,use g_threads_init(),gdk_threads_enter(),gdk_threads_leave() to redraw frames recv from TV card(PAL),
but i can't draw text on the video,i want to use  cairo libarary to manipulate the frame's buffer(had convert to rgb24 format),and then 
draw to drawingarea,it's failed, now i direct manipulate the rgb buffer for draw lines....

now ,i must change my app to c++ with gtkmm ,so that i can use more library,(such as jrtplib,libdcmtk....these lib are c++,...)
i used one thread to capture frame and convert it to rgb24 format.
and want to use a thread to display the captured frame with Gtk::DrawingArea,but i can't found any good way to do these.


1. use one thread to capture and convert raw frame to rgb24 format.( i had done it)
2. use one thread to display the captured frame background in a Gtk::DrawingArea.(not done)
3. use draingarea->get_window() to draw text on the video as foreground of drawing area,line or use cairo to manipulate frame pixels , or 
    direct manipulate pixels ?

thanks.