Devin J. Pohly
50 lines
1.9 KiB
Plaintext
50 lines
1.9 KiB
Plaintext
A sound driver implements RageSoundDriver, and must implement:
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void StartMixing(RageSound *snd);
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void StopMixing(RageSound *snd);
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int GetPosition(const RageSound *snd) const;
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A sound driver may implement, if needed:
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void Update(float)
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Details:
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When a sound is playing, call RageSound::GetPCM(buf, size, pos) to get data.
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"buf" will receive signed, 16-bit stereo PCM data. "pos" must be the position
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at which this sound will be played, in samples relative to GetPosition().
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(That is, when GetPosition() == pos, the first sample is being heard.)
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GetPCM returns the number of bytes placed in buf.
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If GetPCM returns less than size, it has no more data. When this happens,
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1. Do not call GetPCM again unless StartMixing() is called again. (It's
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done; it has no more to say.)
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2. When all data has been flushed from the sound buffer (eg. all sound
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has been heard), call Sound->StopPlaying(). (This tells the sound that
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it's *really* stopped, and can be reused.)
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Notes:
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If StopMixing(snd) is called, do *not* call snd->StopPlaying. It's already
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stopped. Only call snd->StopPlaying when the sound is stopped by a small
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GetPCM return value.
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If there's latency between StartMixing(snd) being called and the sound
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actually being heard, GetPosition can return time less than "pos". For
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example, if the first GetPCM call has a pos of 1000, and it'll take time
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before any sound is actually heard, GetPosition may return values
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less than 1000 if it's called before the sound is heard. (RageSound will
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cope with this.)
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Likewise, GetPosition may return values that havn't actually been queued
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in underrun conditions. For example, if the last GetPCM call had a pos
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of 1000, and returned 100 samples (so it returned samples 1000 through
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1100), GetPosition may return values greater than 1100 in underrun
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conditions.
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A global lock on the sound system can be acquired:
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LockMut(SOUNDMAN->lock);
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The simplest sound driver is WaveOut; use it as an example.
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