Re: very slow drawing

Pasha Murat (murat@cdfsga.fnal.gov)
Sat, 6 Feb 1999 12:30:03 -0600 (CST)


Thomas Walter writes:
> Dear Otto,
>
> > Hi Thomas,
> > I didnt follow all your discussion. Could it be that your macro is too
> > long? At some point (I guess at about 500 lines) the cint buffer which
> > keeps the byte code gets full then cint starts interpreting instead of
> > running the "compiled" code and this is of course very slow
> >
> thanks for your sugestion. The investigations showed, that the problem
> lies somewhere between root and X11 (see priror mails). In the batch mode
> (root -b) I don't have any performance degradations.
>

It seems that this discussion raises a very important issue, related to the
design of ROOT low-level graphics.

- ROOT uses raster (as opposite to vector) graphics, it is pixmaps and not
X11 "draw primitive" commands which are being passed over the network.
Passing pixmaps over the network is not the most time-efficient way
of displaying the graphics images. I think that this explains the problems
experienced by Thomas.

It takes me 10 seconds and even more to redraw a simple canvas
when I'm working from home using X-terminal over the modem (28K) connection.
In this mode there is a drastic difference in performance between ROOT
and PAW graphics with PAW graphics being many (5-10) times faster.
Redrawing of more complex event displays takes minutes.

- any graphics system which is required to be efficient over the network has
to work in client-server mode with the drawing commands and not pixmaps
travelling across the ocean. If I remember it correctly a work on the
implementation of client-server graphics mode for ROOT has started some
time ago but I don't know where the things stand right now. Client-server
mode won't help people using X-terminals, but as these are becoming less
and less popular, I don't think it is a serious issue.

- several big experiments (with Tevatron experiments among them) are planning
to take data in the year of 2000, there definitely
be a lot of physicists using event display programs in the distributed
environment (over the LAN's and WAN's), the issue of performace is a very
important one, so it make sense to have a special discussion of client-server
graphics mode at the ROOT user workshop planned at Fermilab in the end of March.

-pasha