Re: [Audacity-devel] [PATCH] Show default audio I/O device in Preferences

[Martyn S. <mar...@go...>]

Hi Richard

Richard Ash wrote:
> On Sat, 2009-08-22 at 22:16 +0100, Richard Ash wrote:
>> It is real, the problem is that different bits of the audacity code are
>> dealing with needing to find the default audio devices differently. This
>> causes the symptoms Michael describes, however I think the problem was
>> that I didn't agree with his solution to the problem, and failed to get
>> anyone to actually implement anything better.
>>
>> As I said at the time the correct approach is a single method that gets
>> the device and handles the defaults are required, and then is used
>> everywhere when the device is required. This should ensure that the
>> behaviour is consistent and correct.
>>
>> The question is where to put that code, because it could legitimately be
>> considered more relevant in AudioIO than in the preferences, but that
>> poses a problem of not having access to the right objects and
>> references. Should we instantiate AudioIO within the preferences to
>> handle the Audio device layer? Would that cause all sorts of other
>> issues? Casting another way, could we provide (static?) methods in the
>> preferences code that can be used by AudioIO to get the correct default
>> devices?
>>
>> Any suggestions please, for the moment I will work on trying to get the
>> correct code written in the prefs
> This is now done, I have committed the relevant code to select the
> default device from the currently selected API if there is no device
> specified in the preferences. This means if the API is set in the
> preferences, then a device from that API is chosen, even if the global
> default device is from a different API (which has never worked before).
> 
> At the moment these are private methods of the DevPrefs class, because
> that was the easiest place to put them.
> 
>> After that AudioIO is buggy, because it picks the default device
>> regardless of API when there isn't a set device, which could cause
>> further complications ...
> This is now true - if you set the API in the preferences but not the
> devices, then the preferences will honour your choice of API and put in
> default devices from that API (I used OSS for this, default is ALSA).
> However when AudioIO is independently deciding what devices to use for
> sample rate probing etc, it just calls Pa_GetDefaultOutputDevice(),
> which for me returns ALSA. This gives the odd effect where one set of
> devices is shown in the preferences, but another is being used by the
> sample rate probing code, and indeed by playback / recording.
> 
> So the options are:
> * Duplicate the default device choosing logic from DevPrefs in AudioIO,
> so they do the same things
> * Enable AudioIO to call the methods from DevPrefs, except that DevPrefs
> won't be instantiated at the right moments
> * Move the code from DevPrefs to AudioIO and enable DevPrefs to access
> the relevant information from AudioIO when it needs it. I think AudioIO
> is always instantiated when DevPrefs is working, but am not sure how to
> get the reference from one object to the other.
> 
> Anyone like to make some suggestions?

I haven't looked at the code, so this is just a quick comment, but why 
not (in AudioIO) just
    mPlayDevice = gPrefs->Read(wxT("/AudioIO/PlaybackDevice"), wxT(""));
and only use Pa_GetDefaultOutputDevice() if that is ""?

Maybe I misunderstood the question.

TTFN
Martyn

> Richard
> 
>