Re: [pygame] pygame+threading+windows

[James Paige <Bob@xxxxxxxxxxxxxxxxxxx>]

On Thu, Aug 03, 2006 at 05:38:47PM +0200, Lars Friedrich wrote:
> > >
> > >> In general you must use pygame on the main thread. The same is true
> > >> with any cross-platform GUI. You should start other threads for the
> > >> other tasks your application is doing.
> > >
> > > This implies, that all user interfacing is done in the main thread.
> > > What is the usual way to deal with this in an object oriented  
> > > approach?
> > >
> > > My plan was to have several classes that inherit from "Thread" and are
> > > each responsible for a certain part of the GUI. This way I have the
> > > possibility to easily switch one part of my GUI on or off by
> > > instantiating resp. deleting an object of the responsible class.
> > > Learning that one cannot delete Threads and that all GUI-event- 
> > > handling
> > > should be done in the main Thread disappointed me little. What is the
> > > usual structure, if I want to have a highly configurable framework,
> > > with different GUI-Windows, not present in every application?
> > 
> > Why do you think you need threads? Nothing you've said implies a need  
> > or want for threads at all.
> 
> I would like to explain my thoughts using a specific example of my
> project:
> 
> I need to get frames from a camera and display them on the screen. At
> the same time, I have to do some other stuff. I wrote a "Camera"-class
> which has a "getFrame" method, returning a frame in a numpy-array. Now I
> also have a "CamWindow"-Class (that inherits from "Thread") which will
> know which camera's frames are to be displayed. It works like this:
> 
> myCam = Camera(...various options...)
> 
> myCamWindow = CamWindow(myCam)
> 
> myCamWindow.start()
> 
> Now the myCamWindow-Thread calls the "getFrame"-method of "myCam" and
> displays the data, using pygame. The "run"-method of "CamWindow"
> contains a "while 1"-loop with a "sleep"-command inside. If "CamWindow"
> would not be a "Thread", program excecution would stop when this loop is
> entered. That's why I wanted a "Thread".
> 
> I would like to be able to use all these objects in Python's interactive
> mode, since I don't want to make a GUI for every little thing I would
> like to try out.
> 
> Thanks for every comment
> 
> Lars
> 
> 

You do not need threads for what you are trying to do.

Ditch the idea of having a CamWindow.run() method that does and endless 
while loop.

It would be much better for you to provide a CamWindow.update() method 
that just does the check for a new frame *once* and then call 
CamWindow.update() periodically from you main pygame loop.


Or to put it another way, what is the point of having two threads that 
both do:

  while 1:
    do_something
    sleep

  while 1:
    do_something_else
    sleep

When it is much easier to use a single non-threaded loop that does:

  while 1:
    do_something
    do_something_else
    sleep

There /are/ situations where threading is better, but from what you have 
described, I don't think this is one of them.

---
James Paige