refactor rvoice_mixer

[derselbst]

rvoice_mixer needs a bit refactoring after the workaround to fix #192. Think about:

• remove fluid_rvoice_eventhandler_t::is_threadsafe
• remove "synth.parallel-render"
• remove fluid_voice_t::debug
• refactor chrous and reverb types
  • fluid_revmodel_set takes floats.
  • fluid_revmodel_presets_t uses fluid_real_t
  • fluid_revmodel_t uses fluid_real_t
  • fluid_rvoice_mixer_set_chorus_params takes doubles
  • fluid_rvoice_mixer_set_reverb_params take doubles
  • fluid_rvoice_event_t::realparams is fluid_real_t.
  • public synth API takes doubles
  • etc.
• each rvoice gets its own mono resampled buffer[FLUID_MIXER_MAX_BUFFERS_DEFAULT*FLUID_BUFSIZE]?
• openMP parallelization?
• get rid of that hug macro magic switch case in rvoice_event_handler
• variable naming not very intuitive (buf_blocks, buf_count, current_blockcount ???)
• loop that initializes rvoice buffer in fluid_rvoice_buffers_check_bufnum() is superfluous
• efficiently render "silence"
• rethink fluid_synth_check_finished_voices()
• fluid_rvoice_set_output_rate() is called twice (by fluid_voice_set_output_rate() and fluid_rvoice_mixer_set_samplerate())
• process effects units in parallel

[jjceresa]

About the mixer.

variable naming not very intuitive (buf_blocks, buf_count, current_blockcount ???)

Some infos follow:

• buf_count: is the number of buffers .
  This number depends of the number of audio output. This number is specified by mixer->buffers.buf_count. (Probably a better naming should be related to the audio output number).

• Internally each buffer have the same maximum size (buf_blocks). (not a good name too).

• The size of a buffer (buf_blocks) is specified in blocks. Each block have FLUID_BUFSIZE samples

• current_blockcount: is the current index (0 to buf_blocks) of the block been mixed.

---

Some images show the internals links from 'detail to top':

The buffs table pointers keeps the mixer independent of the real buffers structure.

---

The caller requests blockcount block (each block is FLUID_BUFSIZE sample size ).
The function returns the real blocks number processed.

[derselbst]

Thanks for this illustration!