[SDL] Problem filtering events (from another application's thread?)

[Eric Kort]

I think I figured out my problem...I have no main event loop (pretty
obvious in retrospect)!  So the events were getting queued up, and I
could access them with SDL_PollEvent the next time the user entered a
command from my library.  Since I wanted real time event processing for
repaints, resizes, etc., I created a separate event processing thread
with SDL_CreateThread which polls for events and is started by my
sdlOpen function.  This thread then runs along side R's application
thread and catches events in real time.

-Eric 

On Mon, 2006-06-05 at 17:16 -0400, Kort, Eric wrote:
> Hello.  I am trying to write an image viewer library for the R framework
> (www.r-project.org) based on SDL (which I call "rsdl").  (R has rich
> graphics plotting capabilities, but rendering large-ish images is quite
> slow).
> 
> I am able to display an image loaded in R in an SDL window without any
> problem.  This is via a shared library which R loads (when I load my
> rsdl library within R), containing the SDL related code ("rsdl.so").  My
> problem is that I am not able to filter events.  From within R I call an
> sdl.open() function which in turn calls the sdlOpen symbol defined in
> the shared library.  The sdlOpen function creates the SDL window, and
> installs an event filter like this:
> 
> ...
>     screen = SDL_SetVideoMode(INTEGER(w)[0], INTEGER(h)[0], 32,
> 
>        SDL_SWSURFACE|SDL_ANYFORMAT|SDL_RESIZABLE);
>     SDL_EventState(SDL_KEYDOWN, SDL_IGNORE);
>     SDL_EventState(SDL_KEYUP, SDL_IGNORE);
>     SDL_EventState(SDL_VIDEORESIZE, SDL_ENABLE);
>     printf("events enabled...\n");
>     SDL_SetEventFilter((SDL_EventFilter)filterEvents);
> ...
> 
> But the filter never gets (visibly) triggered.  Here is my filter:
> 
> int filterEvents(SDL_Event *event) {
>    printf("Caught Event...");
>   if (event->type == SDL_VIDEOEXPOSE) {
>     printf("Screen needs refresh...");
>     SDL_UpdateRect(screen, 0, 0, screen->w, screen->h);
>     return(0);
>   }
>   if (event->type == SDL_VIDEORESIZE) {
>     printf("Resizing...");
>     if (paint) 
>       repaint();
>     SDL_UpdateRect(screen, 0, 0, screen->w, screen->h);
>     return(0);
>   }
>   return(1);
> }
> 
> When I click in the window or resize it, I never see the "Caught event"
> message, and it is apparent from subsequent rendering that the program
> still thinks the window is its original size.
> 
> My sense is that the problem is that the window was created from another
> thread (R's thread), and I am not able to filter events from that
> thread.  Is it apparent to anyone how I might work around this?
> 
> Thanks,
> Eric
> 
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