Re: how to write a mixer using alsa lib api ?

[Takashi Iwai <tiwai@suse.de>]

At Mon, 24 Nov 2003 00:01:53 +0100,
Christian Esken wrote:
> 
> On Tuesday 21 October 2003 11:16, Tommi Sakari Uimonen wrote:
> > > and I want to know where I find some documnent to know
> > > how to use these alsa lib api,namely,I want a
> > > specification of these api,thanks a lots .
> >
> > http://www.alsa-project.org/alsa-doc/alsa-lib/
> 
> Nice hint. But your comment is barely nothing more than a RTFM. If the mixer 
> documentation would be usable this would be OK. But actually the 
> documentation is lacking a lot, especially with the mixer interface. Need an 
> example:
> 
> int snd_mixer_poll_descriptors()
> Documnetation says: "get poll descriptors"
> 
> Cool: "get poll descriptors". I wanted to do this my whole life. :) Whatever 
> these "poll descriptors" do, I do not know. But it is important, or is it 
> not?!? :-(
> 
> More questions: Why are there multiple API's: Should I use the "normal" or the 
> "simple" API (BTW:The simple mixer interface from mixer/simple.c is not on 
> the Web).
> 
> Need more examples:
> snd_mixer_set_callback()
> What good is this function for? A callback for what? And is this optional, 
> just to avoid polling or and explicite update or what?
> 
> snd_mixer_elem_attach()
> Documentation say: "Attach an HCTL to an opened mixer."
> Whatever an HCTL might be, I don't know. Why I should do it, I do not know as 
> well. The snd_mixer_attach() documentation does not tell me. It also does not 
> tell me what is an in- or out-parameter and if I have to allocate the memory 
> for the data (if there are any) of the out-parameter myself.
> 
> snd_mixer_elem_type_t snd_mixer_elem_get_type ( const snd_mixer_elem_t * obj ) 
> Documentation does not tell me what types exist: snd_mixer_elem_type_t is not 
> hyperlinked and neither be found under "Data Structures" nor under "Data 
> Fields"
> 
> Sorry if my posting sounds rude, but I am fighting since months with the mixer 
> API and the frustration is growing: I am not even able to read the correct 
> playback volume if another application changes it. I went to reading the 
> alsa-lib source, because alsamixer is not a really good example (it also has 
> no documentation). 
> 
> Sorry again, but with ALSA1.0 approaching, the documentation clearly needs an 
> upgrade: The Mixer is not even contained in the "Module Index" of the 
> mentioned web page.
> Telling application developers that want to push ALSA to RTFM is not the right 
> way IMHO. 

about the mixer application, it'd better to wait for a while.

in parallel with the release of ALSA 1.0, Jaroslav is working on the
higher abstraction layer for mixer.  this will be definitely easier to
use for normal cases rather than the still complex abstraction as it
is.


Takashi


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