At Wed, 10 Mar 2004 15:16:34 +0100, Ove Kaaven wrote: > > > Please start writing what the API should provide. > > Well, the requirements that raised this thread should be fairly clear. > For example, > > ALTERNATIVE 1 > > snd_pcm_set_volume(snd_pcm_t* pcm, int volume) > > and > > snd_pcm_set_pan(snd_pcm_t* pcm, int pan)
it'd be cleaner to separate these features from the existing snd_pcm stuffs. i.e. i'd like to see rather another class, with simplified parameter setting and extended features. > using whatever value range makes the most sense, and perhaps some query > on whether these controls are available from the pcm info. It's > acceptable to have to explicitly ask for these controls using hw_params. hw_params is not a good candidate because it's a setup parameter at the initialization but not applied to the running streams. so, we need another record which is applicable dynamically during the stream is running. > The plug plugin could insert the route/volume plugin if these controls > are asked for. agreed. the plugin solution sounds nice. > ALTERNATIVE 2 > > snd_pcm_set_volume(snd_pcm_t* pcm, int vol_left, int vol_right) > > but I don't expect this to be useful, since there are probably some > oddball devices out there that aren't able to control left and right > volume independently like this. again plugin in such a case? > ALTERNATIVE 3 > > Let each PCM channel have its own mixer control, like the EMU10K1 > currently do. That is, use snd_pcm_info_get_subdevice() to get the > index, then look up a volume control with a well-known name and the > given index using the snd_ctl API to control the volume of that PCM > stream. The name and semantics of that mixer control would have to be > standardized and be the same on all devices that are capable of this > feature. such an implementation detail will be anyway hidden in the library, and shouldn't appear in the API itself. > Whatever way is chosen, it's simple enough to work with. > > But if we get into the realm of spatial sound, it can get trickier, of > course. I might suggest to create a new snd_pcm_fx_params_t or > something, which can be loaded into a PCM stream to change the volume, > pan, or other effect. The available effects should depend on which was > requested in hw_params. Specifically, the following effects would be > desirable: > > * Volume > * Pan (not available if 3D sound is requested) > * Frequency (can be used for software-calculated doppler shift, or for > "wavetable synthesis"-like purposes) > * 3D position (relative to listener) > * Velocity (for hardware-calculated doppler shift) > * Cone inside/outside angles, direction, outside volume > * Min/max distance (wherever the sound is heard) hmm, the question is how abstracted the ALSA API should be. we have the openAL layer on the ALSA hw API. so, the lower implementation isn't necessarily too generalized. > There are also settings that can be considered "global" for all sounds > in the game, but I'm not sure how they could really be considered such > using the PCM API, so it's acceptable to have to go through every PCM > stream and update the parameters of each one, if that's easier to > implement. If not, there must be a way to attach each 3D-aware PCM > stream to some kind of master structure which can hold these parameters. > This master can be a designated PCM stream with special hw_params. > Global settings include: > > * 3D position, orientation (forward and upward directions), and velocity > of listener, to allow streams to use absolute, not relative, > coordinates, if they want to > * Distance, rolloff, and doppler factors (I don't remember the exact > semantics of these, but can look it up) > > These will be required anyway for full HW-accelerated OpenAL support, of > course. > > The API should also be designed to allow for further parametrized > effects to be applied to a particular stream, for example reverb > effects. For what it's worth, DirectSound has currently defined Gargle, > Chorus, Flanger, Echo, Distortion, Compressor, and a couple of Reverb > types... this reminds me the use of LADSPA plugins. if the samples are handled in float internally, we can use LADSPA plugins quite easily. the calculation of float is cheap nowadays, the only cost is conversion between different types. Takashi ------------------------------------------------------- This SF.Net email is sponsored by: IBM Linux Tutorials Free Linux tutorial presented by Daniel Robbins, President and CEO of GenToo technologies. Learn everything from fundamentals to system administration.http://ads.osdn.com/?ad_id=1470&alloc_id=3638&op=click _______________________________________________ Alsa-devel mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/alsa-devel
