On 20.06.2012, at 21:32, 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.

There may be two issues here: 

1: since you are using threads, make sure that you don't create or delete windows from within a thread. All FLTK calls should be done in the main thread. That is a restriction of the underlying system calls. If you need to do FLTK stuff in threads, you need to use Fl::lock, ::unlock, and ::awake.

2: your mein thread must return from callbacks quickly. I don;t know much about boost, but if the call above blocks the FLTK main loop, you will not get any updates until you return from the callback (or call Fl::check() or Fl::wait(), but that has its own issues).

 - Matthias