>Does anyone have experience with VNC on a Windows CE device and can give me
>some hints for a faster reaction ?
There are several things working against you. GDI on CE is so slow that the process of
drawing interferes with the network bandwidth. If you are going through a serial
link, this
interference is actually great enough to cause transmission errors and retransmissions,
which slaughters your ability to transmit.
Also, on a really good day, if you didn't have to do anything else, you can get around
2-3 full screen updates per second on a palm sized CE device. Compared to the 40+
updates
per second that plain GDI is capable of on generic desktop machines, this is pathetic.
Also, that is 3/sec for a 240x320 screen, not for the potentially 1024x768 screen your
host is
probably using.
One of the early things I did was to drop the thread priority of the drawing code to
very low.
This kept it from interfering with the serial driver and network stack, which
decreased the
amount of transmission errors. I also, when I had access to the PPP protocol being
used,
dropped the MTU to 150bytes so that the amount of information to retransmit was
minimized,
which optimized throughput, even though the packet overhead was immense.
I am working on modifications to the TridiaVNC sources to take advantage of Tight
Encoding
and ZLib compression. My modifications use GAPI for "direct" video hardware access.
I say "direct" because it quite obviously is not actually direct on the unit I have.
A great many
of my problems stem from the fact that the manufacturer thinks all programmers are
idiots and
double buffers the "direct" video access, thus halving the video performance and
causing screen
overwrite problems that would not exist if it simply did what it was supposed to do.
My modifications are not applicable to general purpose use, however, because I am
using a
desktop from Linux that is actually sized to 240x320. My code has no support for
scrolling or
scaling to handle larger desktops. In this situation, I have been able to achieve
noticeable
speed improvements, but it is still a dog compared to desktop performance. Until CE
makers
start making useful hardware, video performance is going to be incredibly bad.
With my modifications, I can set the MTU back up to 1500bytes, and can still achieve
full
theoretical bandwidth for the serial link (actually better than full, because PPP
compresses).
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