How to prevent UI updates interfering with user's actions?

[Carsten A. Arnholm]

Hello,

I am using wxWidgets 2.8.4 (Ansi) on Windows XP and Linux Kubuntu 7.04. 
Using VS2005 Express C++ compiler on Windows and GCC on Linux.

I am working on an application that controls a webcam, and I am having some 
issues with the dialog shown here: 
<http://www.arnholm.org/tmp/camera_properties.jpg> . The dialog is derived 
from wxPropertySheetDialog and each tab is derived from wxPanel.

The dialog allows the user to change typical camera properties: Brightness, 
Gamma, Gain etc. using various controls such as sliders, radio boxes and 
more. This works ok and the camera display responds as it should.

However, the camera properties are "volatile", they can change without the 
user using the controls shown (I don't go into the details about why here, 
but there are real reasons why it happens). It is therefore needed to 
frequently update the controls to reflect the actual state of the camera 
properties. I have also written required code to do this. Currently this is 
triggered using a timer in the active tab, every second or so the timer 
fires an event and the controls are updated by reading from the camera.

The problem is that when the user tries to drag a slider, this gets 
overridden by the timer event slider update. At one stage I thought I could 
avoid this by SetFocus/KillFocus events and block the timer updating the 
controls when the user was busy doing it, but now I can't seem to get 
SetFocus/KillFocus events to work at all.

I wonder what I am doing wrong here. I have tried removing the timer and 
using idle processing instead, but that seems even more aggressive.

In summary: How can I update the controls from within the program without 
interfering with the user when he/she is updating something?

I hope this is clear enough and would appreciate any suggestions....

Thanks
Carsten A. Arnholm
http://arnholm.org/
N59.776 E10.457