Re: [boost] interest in a "signal flow" library?

From: Paolo Coletta (paolo_at_[hidden])
Date: 2007-02-21 09:08:34

> Is there any interest in a library which facilitates the
> implementation and interconnection of objects using Boost.Signals?
        
Yes, much interest.
        
> For example, in a video processing scenario, one might be using the
> following objects:
> 
>  * frame_rate - generates a void() signal at a consistent frame rate
>  * video_generator - upon receiving a void() signal, produces a signal
> containing an image (e.g., a frame grabbed from a camera or read from
> a file)
>  * differencer - upon receiving an image signal, outputs the
> pixel-difference between the image and the previous image received
>  * flipper - upon receiving an image signal, outputs the horizontally
> flipped image
>  * analysis - upon receiving an image signal, performs some sort of
> analysis and outputs a feature vector signal
>  * database - upon receiving a feature vector signal, outputs an image
> from the database based on some relationship
>  * display1, display2 - upon receiving an image, displays it in a window
> 
> It would be nice to be able to easily connect these objects via
> intuitive signal flow "diagrams":
> 
> // perform the whole video analysis and display the results
> frame_rate >>= video_generator >>= differencer >>= flipper >>=
>  analysis >>= database >>= display1;
> 
> // also display the video input
> video_generator >>= display2;
> 
> ... or, to specify the entire signal flow in one shot using something like this:
> frame_rate
>>>= video_generator
>         >= (differencer >>= flipper >>= analysis >>= database >>= display1)
>         >= display2;
> 
        
I didn't look at the library yet, however, in a similar context I had the
requirement to perform some operations in parallel. Thus, I wonder if this
could be supported by the syntax, e.g., 
   
video_generator >>= ( effect1 && effect2 ) >>= image_sum >>= display
     
where effect1 and effect2 are executed in parallel (for example, by
different threads of a thread_group); image_sum (which expects two
arguments) is executed only when both effect1 and effect2 are completed.
       
Regards,
     Paolo