SDL2: fix mixer errors, mixer.init(..., allowchanges=0)

[dlon]

Close #860

[illume]

Ah. SDL 2 is required for the allowchanges stuff to work.
https://wiki.libsdl.org/SDL_OpenAudioDevice#allowed

• SDL_AUDIO_ALLOW_FREQUENCY_CHANGE
• SDL_AUDIO_ALLOW_FORMAT_CHANGE
• SDL_AUDIO_ALLOW_CHANNELS_CHANGE
• SDL_AUDIO_ALLOW_ANY_CHANGE

With SDL1 (and pygame), I think it defaulted to 0 behaviour.

[illume]

I wonder if we should let channels to go through as a number more than 2? I guess none of the code is prepared for this really (sound array etc), and it would require testing. But SDL2 accepts more than 2.

https://wiki.libsdl.org/SDL_AudioSpec#Remarks

channels specifies the number of output channels. As of SDL 2.0, supported values are 1 (mono), 2 (stereo), 4 (quad), and 6 (5.1). 

[illume]

So, I guess this channels >= 2 test should only be for SDL1.
For SDL2 it should check for 1, 2, 4, and 6.

[dlon]

Edit: Just saw the edit allowedchanges=0 doesn't cause it to fail. SDL converts the audio to and from the requested format instead of using a similar one (in the callbacks). Seems to be the default behavior in SDL 1 Den fre 1 mars 2019 06:14René Dudfield <notifications@github.com> skrev:

…

Ah. SDL 2 is required for the allowchanges stuff to work. https://wiki.libsdl.org/SDL_OpenAudioDevice#allowed - SDL_AUDIO_ALLOW_FREQUENCY_CHANGE - SDL_AUDIO_ALLOW_FORMAT_CHANGE - SDL_AUDIO_ALLOW_CHANNELS_CHANGE - SDL_AUDIO_ALLOW_ANY_CHANGE With SDL1 (and pygame), I think it defaulted to SDL_AUDIO_ALLOW_ANY_CHANGE behaviour. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#861 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ACh9LW3aAVga3h3H3y_ExH4cgYiwbz6Cks5vSLctgaJpZM4bXsSK> .

[dlon]

This also solved the issues in #850.

[charlesej]

Good changes and good idea providing the allowedchanges argument.

[dlon]

From the SDL 1.2.15 docs:

int SDL_OpenAudio(SDL_AudioSpec *desired, SDL_AudioSpec *obtained);

This function opens the audio device with the desired parameters, and returns 0 if successful, placing the actual hardware parameters in the structure pointed to by obtained. If obtained is NULL, the audio data passed to the callback function will be guaranteed to be in the requested format, and will be automatically converted to the hardware audio format if necessary.

From SDL_mixer (1.*):

/* Open the mixer with a certain desired audio format */
int Mix_OpenAudio(int frequency, Uint16 format, int nchannels, int chunksize)
{
	int i;
	SDL_AudioSpec desired;

...

	/* Set the desired format and frequency */
	desired.freq = frequency;
	desired.format = format;
	desired.channels = nchannels;
	desired.samples = chunksize;
	desired.callback = mix_channels;
	desired.userdata = NULL;

	/* Accept nearly any audio format */
	if ( SDL_OpenAudio(&desired, &mixer) < 0 ) {
		return(-1);
	}
...
}

obtained is not NULL (it's &mixer), so I guess allowedchanges=0 is the wrong default. But changing it causes a bunch of test failures, so I guess we update the tests instead.

I set the default to AUDIO_ALLOW_FREQUENCY_CHANGE | AUDIO_ALLOW_CHANNELS_CHANGE, which is the same default that SDL2_mixer uses.

[husano896]

#113 can be closed since channels > 2 are supported in SDL2.