virtualx-engine/servers/audio/audio_stream.cpp

/*************************************************************************/
/*  audio_stream.cpp                                                     */
/*************************************************************************/
/*                       This file is part of:                           */
/*                           GODOT ENGINE                                */
/*                    http://www.godotengine.org                         */
/*************************************************************************/
/* Copyright (c) 2007-2017 Juan Linietsky, Ariel Manzur.                 */
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/*************************************************************************/
#include "audio_stream.h"

//////////////////////////////



void AudioStreamPlaybackResampled::_begin_resample() {

	//clear cubic interpolation history
	internal_buffer[0]=AudioFrame(0.0,0.0);
	internal_buffer[1]=AudioFrame(0.0,0.0);
	internal_buffer[2]=AudioFrame(0.0,0.0);
	internal_buffer[3]=AudioFrame(0.0,0.0);
	//mix buffer
	_mix_internal(internal_buffer+4,INTERNAL_BUFFER_LEN);
	mix_offset=0;
}

void AudioStreamPlaybackResampled::mix(AudioFrame* p_buffer,float p_rate_scale,int p_frames) {

	float target_rate = AudioServer::get_singleton()->get_mix_rate() * p_rate_scale;

	uint64_t mix_increment = uint64_t((get_stream_sampling_rate() / double(target_rate)) * double( FP_LEN ));

	for(int i=0;i<p_frames;i++) {



		uint32_t idx = CUBIC_INTERP_HISTORY + uint32_t(mix_offset >> FP_BITS);
		//standard cubic interpolation (great quality/performance ratio)
		//this used to be moved to a LUT for greater performance, but nowadays CPU speed is generally faster than memory.
		float mu = (mix_offset&FP_MASK)/float(FP_LEN);
		AudioFrame y0 = internal_buffer[idx-3];
		AudioFrame y1 = internal_buffer[idx-2];
		AudioFrame y2 = internal_buffer[idx-1];
		AudioFrame y3 = internal_buffer[idx-0];

		float mu2 = mu*mu;
		AudioFrame a0 = y3 - y2 - y0 + y1;
		AudioFrame a1 = y0 - y1 - a0;
		AudioFrame a2 = y2 - y0;
		AudioFrame a3 = y1;

		p_buffer[i] = (a0*mu*mu2 + a1*mu2 + a2*mu + a3);

		mix_offset+=mix_increment;

		while ( (mix_offset >> FP_BITS) >= INTERNAL_BUFFER_LEN ) {

			internal_buffer[0]=internal_buffer[INTERNAL_BUFFER_LEN+0];
			internal_buffer[1]=internal_buffer[INTERNAL_BUFFER_LEN+1];
			internal_buffer[2]=internal_buffer[INTERNAL_BUFFER_LEN+2];
			internal_buffer[3]=internal_buffer[INTERNAL_BUFFER_LEN+3];
			_mix_internal(internal_buffer+4,INTERNAL_BUFFER_LEN);
			mix_offset-=(INTERNAL_BUFFER_LEN<<FP_BITS);
		}
	}
}