A possible compression scheme

Robert de Bath rd103935 "at" mayday.cix.co.uk
Sun, 04 Oct 1998 22:47:46 +0000

On the list for 2 days an I see my idea being aired. :-) :-(

I too think it'd be a very good idea to give vnc some 'off-screen video
memory'. If there's enough of it can be used for all the things an
X-server uses the extra ram on a normal video card... mouse pointer
background, 'tiles and stipples', line segments, font cache,
'saved-unders' and saving the root window's pixmap.

On a similar note, but probably much more difficult, there's the idea of 
Z-dimension compression.  Most of the 'screen furniture' of an X (or 'doze)
screen tends to have only a few colours I think a new subtile type that
has 16 or probably only 4 colours in the raw subtile could compress detail,
like icons, quite a bit better than 24bit hextiles.

The third thing isn't compression but it might improve the 'feel' of the
display, especially over slow (modem) links. Simply, the idea is to have
a 'sprite' for the mouse pointer like some of the Windows graphics
cards. (I think the S3 has this and my C&T 65554 definitly does)
That way the local vnc client can change the _real_ mouse pointer to the
X cursor of the moment, not just a dot!

BTW: Does anyone know offhand what this means ...

"XAA: CPU to screen color expansion (bitmap, TE/NonTE imagetext, TE/NonTE polytext)"

XFree86 on a C&T 65554 has this too ... whatever it is.

Rob.                           (Robert de Bath <http://www.cix.co.uk/~mayday>)
-- Sorry, weekend email only ATM. (Urgent to Robert.deBath "at" colt.de)

On Sun, 4 Oct 1998, Alan Cox wrote:

> > The other approach is to actually have some sort of backing store in the
> > client but hope to cope with this cleanly is a tricky question.
> Real X servers keep offscreen caches of rectangles in videoram. You can
> already tell VNC clients to move a rectangle in their own space. So if
> you had a logical and display size seperately in VNC you seem to have all
> the pieces for cache management
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