[gmpi] Re: Querying a plugin's structure (params, IOs, etc)

On Mon, Dec 12, 2005 at 11:15:19PM -0800, thockin@xxxxxxxxxx wrote:
> On Fri, Dec 02, 2005 at 02:43:54PM -0800, thockin@xxxxxxxxxx wrote:
> > Anyone have opinions?  This is one of those fundamental design choices
> > that can set precedent for other aspects of the API...
> 
> How about soemthing like this? (pseudo-code) (discussion below)

I know it's holiday time for many people, myself included.  If anyone gets
a few free minutes, I wouldn't mind input, still..

>  /*
>   * A plugin is essentially a tree of elements.  You can inspect the tree,
>   * one group at a time.
>   */
> 
>  enum GMPI_ElementType {
>       GMPI_ELEM_AUDIO,
>       GMPI_ELEM_CONTROL,
>       GMPI_ELEM_GROUP
>  }
> 
>  /* an element is a single piece of a plugin */
>  GMPI_Element {
>       GMPI_ElementType type;
>       uint32_t key;
>       char* name;
>  }
> 
>  GMPI_Plugin {
>       ...
>       Inspect(uint32_t group, int index, GMPI_Element* element);
>       GetAudioIO(uint32_t key, GMPI_Unknown* unknown);
>       GetControlIO(uint32_t key, GMPI_Unknown* unknown);
>       ...
>  }
> 
>  GMPI_AudioIO {
>       ...
>       GetDirection(void);
>       GetChannels(void);
>       GetEncoding(void);
>       ...
>  }
> 
>  GMPI_ControlIO {
>       ...
>       GetType(void);
>       GetDirection(void);
>       ...
>  }
> 
>  GMPI_FloatControl {
>       ...
>       GetType(void);
>       GetDirection(void);
>       GetMin(void);
>       GetMax(void);
>       GetDefault(void);
>       ...
>  }
> 
>  GMPI_IntControl {
>       ...
>       GetType(void);
>       GetDirection(void);
>       GetMin(void);
>       GetMax(void);
>       GetDefault(void);
>       ...
>  }
> 
>  host internals:
>  --------
> 
>  main loop {
>       ...
>       Find and load a plugin
>       InspectGroup(plugin, GMPI_GROUP_ROOT);
>       ...
>  }
> 
>  InspectGroup(GMPI_Plugin* plugin, uint32_t group) {
>       GMPI_Element element;
>       int index = 0;
> 
>       while (plugin->Inspect(group, index, &element) == GMPI_SUCCESS) {
>               if (element.type == GMPI_ELEM_GROUP) {
>                       /* recurse into a sub-group */
>                       InspectGroup(plugin, element.key);
>               }
> 
>               /*
>                * we found an element - save it's object
>                */
> 
>               if (element.type == GMPI_ELEM_AUDIO) {
>                       /*
>                        * An audio IO
>                        */
>                       GMPI_Unknown* unknown;
>                       GMPI_AudioIO* audio;
>                       plugin->GetAudioIO(key, &unknown);
>                       unknown->QueryInterface(IID_AUDIO_IO, &audio);
>                       SaveAudio(plugin, audio, element);
>               } else if (element.type == GMPI_ELEM_CONTROL) {
>                       /*
>                        * Some sort of control - but what kind?
>                        */
>                       GMPI_Unknown* unknown;
>                       GMPI_Control* control;
>                       plugin->GetControlIO(key, &unknown);
>                       unknown->QueryInterface(IID_CONTROL_IO, &control);
> 
>                       switch (control->Type()) {
>                       case GMPI_CONTROL_FLOAT: {
>                               /*
>                                * a float control
>                                */
>                               GMPI_FloatControl* floatControl;
>                               control->QueryInterface(IID_FLOAT_CONTROL,
>                                               &floatControl);
>                               SaveControl(plugin, floatControl, element);
>                               break;
>                       }
>                       case GMPI_CONTROL_INT: {
>                               /*
>                                * an int control
>                                */
>                               GMPI_IntControl* intControl;
>                               control->QueryInterface(IID_INT_CONTROL,
>                                               &intControl);
>                               SaveControl(plugin, intControl, element);
>                               break;
>                       }
>                       }
>               }
>               index++;
>       }
>  }
> 
> 
> Essentially, the host walks the plugin's tree of elements, figuring out
> what they are along the way, and getting handles to them.  For controls,
> it can specialize down to a type-specific interface.
> 
> This results in a unique interface class for each type of control.  Each
> interface has a number of small data-query methods.  Because we agreed
> that *all* methods return GMPI_Result and take pointers to out parameters,
> these are not quite as simple as I have illustrated.  I'd like to argue
> that sometimes it is ok to just return a value.  For example, if
> QueryInterface returned a void*, then catcher could implicitly convert
> types instead of needing reinterpret_cast<>.
> 
> This is just one model.  It makes sense to me, but it is pretty highly
> normalized.  I'm open to ideas.
> 
> > On Tue, Nov 29, 2005 at 04:28:34PM -0800, thockin@xxxxxxxxxx wrote:
> > > We've got very basic plugins that can be found and loaded.
> > > 
> > > Now how do we find out what they do?  The host has to figure out all the
> > > control inputs, control outputs, audio inputs, audio outputs, etc.  There
> > > are a lot of potential models, I'd like to hear some reasons to go with
> > > one or the other or something totally different.
> > > 
> > > Remember that we need to be able to extract a lot of data:
> > >   * control ports
> > >     - name
> > >     - data type
> > >     - range
> > >     - flags
> > >   * audio ports
> > >     - name
> > >     - format
> > >     - channels
> > >   * nested sub-groups of the above
> > >   * channels
> > >   * ..and more
> > > 
> > > Some ideas I've already heard:
> > > 
> > > 1) Host loops from 0 to n, asking the plugin for metadata about "thing x".
> > > The metadata explains what each thing is.
> > > 
> > > 2) Host asks for structure and gets back an XML blob that represents
> > > everything.
> > > 
> > > What else?  What makes the most sense?  What will be easy to program and
> > > easy to expand?
> > > 
> > > Tim
> > > 
> > > ----------------------------------------------------------------------
> > > Generalized Music Plugin Interface (GMPI) public discussion list
> > > Participation in this list is contingent upon your abiding by the
> > > following rules:  Please stay on topic.  You are responsible for your own
> > > words.  Please respect your fellow subscribers.  Please do not
> > > redistribute anyone else's words without their permission.
> > > 
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> > > Email gmpi-request@xxxxxxxxxxxxx w/ subject "unsubscribe" to unsubscribe
> > > 
> > 
> > -- 
> > Tim Hockin
> > thockin@xxxxxxxxxx
> > Soon anyone who's not on the World Wide Web will qualify for a government 
> > subsidy for the home-pageless.
> > 
> > ----------------------------------------------------------------------
> > Generalized Music Plugin Interface (GMPI) public discussion list
> > Participation in this list is contingent upon your abiding by the
> > following rules:  Please stay on topic.  You are responsible for your own
> > words.  Please respect your fellow subscribers.  Please do not
> > redistribute anyone else's words without their permission.
> > 
> > Archive: http://www.freelists.org/archives/gmpi
> > Email gmpi-request@xxxxxxxxxxxxx w/ subject "unsubscribe" to unsubscribe
> > 
> 
> -- 
> Tim Hockin
> thockin@xxxxxxxxxx
> Soon anyone who's not on the World Wide Web will qualify for a government 
> subsidy for the home-pageless.
> 
> ----------------------------------------------------------------------
> Generalized Music Plugin Interface (GMPI) public discussion list
> Participation in this list is contingent upon your abiding by the
> following rules:  Please stay on topic.  You are responsible for your own
> words.  Please respect your fellow subscribers.  Please do not
> redistribute anyone else's words without their permission.
> 
> Archive: http://www.freelists.org/archives/gmpi
> Email gmpi-request@xxxxxxxxxxxxx w/ subject "unsubscribe" to unsubscribe
> 

-- 
Tim Hockin
thockin@xxxxxxxxxx
Soon anyone who's not on the World Wide Web will qualify for a government 
subsidy for the home-pageless.

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