Conference noted::hackers

1827.0. "Psuedo/true-color X-windows capture" by SAYER::ELMORE (Steve [email protected] 4123645893) Sun Feb 16 1997 21:13

    Is there any expertise in X here?  I have tried the X conference, 
    Open3D, and multimedia_services without much success.  
    
    I have a customer seeking advice on how to capture a workstation screen
    whose root is defined in Psuedo-color but has some individual windows
    in true-color.  Here is his mail:
    
    
>     Hi.
>
>     We spoke briefly in the hallway while you were at Picker MR
>     a few days ago. 
>
>     I have a problem with a system running Dec UNIX 4.0a and X/Motif.
>     (The problem is not OS or system specific, but it might make a
>     difference later.) 
>
>     The system has a 24 bit color card and the J300 video capture card.
>     We have set up our /usr/lib/X11/xdm/Xservers file to start the system
>     in pseudo color mode even though it is true color capable. We then
>     have some windows on the screen that use true color X visuals and
>     some
>     that use pseudo color. This works OK and saves memory and time when
>     the windows that use the default (pseudo color) visual are moved
>     around.
>
>     The problem comes up when we do video capture. That routine reads
>     pixels from the root window in order to capture the entire screen.
>     The
>     root window defaults to a pseudo color visual,  so the video capture
>     data is only 8 bits deep and is often the wrong value. Somehow we
>     need to
>     read the data from a source that has the full 24 bit pixels. 
>
>     Video capture works OK if we don't force the default visual to be
>     pseudo color, since then the root window comes out as true color and
>     the captured data looks fine. However, then we pay a price in
>     performance and memory usage since all our pixmap data triples in
>     size (from 8 to 24 bits). This can be 100s of megabytes in some
>     cases.
>
>     So, my problem is:
>
>        How can I read 24 bit pixel data from the frame buffer for video
>        capture when the X root window is set up with an 8 bit pseudo
>        color
>        visual? Is there a way to read directly from the frame buffer and
>        bypass X altogether ?
>
>
>     I hope this explanation makes some sense. Please let me know if you
>     have any ideas about this, or other sources I might try for help.
>
>       Thanks.
>               Don Russell
    
    
    Any ideas in this conference?
    
    Thanks, Steve