On 20 Jun 2012, at 20:32, William wrote:

>> Hello, I'm fairly new to FLTK but I am having some trouble getting a Fl_Valuator to update from a callback.  I currently have the following callback on a button:
>> 
>> {
>>  boost::thread t(boost::bind(&MotorControl::Sweep, motor_control));
>> }
>> 
>> This should call the MotorControl::Sweep method in a separate thread.  Within this method I issue the value(int) method on a few Fl_Valuators to change their values. There is also a boost sleep command between these method calls.
>> 
>> My issue is if I do not move the mouse, the Fl_Valuators (which are horizontal sliders) do not update their positions.  When I do move the mouse, the sliders instantly jump to their correct values.
>> 
>> How can I get the "Fl_Value_Slider"s to update correctly without me moving the mouse?
>> 
>> Thank you!
> 
> 
> I found a solution that seems to work.  Calling Fl::check(); after setting with value(int) does the trick.

Actually, that is almost certainly the wrong way to go - see Matthias' post...

You need to read the manual (section 10 of the fltk-1.1 manual, or the "Advanced FLTK" section of the fltk-1.3 manual) and follow some of the recipes suggested there.

In summary though, calling Fl::check() from any thread other than the "main" thread is likely to croak in odd ways at some point (how and when is platform dependent!) so you need to us Fl::awake() instead, and you really do want to Fl::lock() and unlock() any widget accesses from the worker threads.