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/*
Copyright 2018 Google Inc. All Rights Reserved.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS-IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
#ifndef RESONANCE_AUDIO_AMBISONICS_AMBISONIC_LOOKUP_TABLE_H_
#define RESONANCE_AUDIO_AMBISONICS_AMBISONIC_LOOKUP_TABLE_H_
#include <vector>
#include "base/spherical_angle.h"
namespace vraudio {
// Represents a lookup table for encoding of Ambisonic periphonic sound fields.
// Supports arbitrary Ambisonic order and uses AmbiX convention (ACN channel
// sequencing, SN3D normalization).
class AmbisonicLookupTable {
public:
// Creates Ambisonic (AmbiX) encoder lookup table given the
// |max_ambisonic_order| used by the client. AmbiX convention uses ACN channel
// sequencing and SN3D normalization.
explicit AmbisonicLookupTable(int max_ambisonic_order);
// Gets spherical harmonic encoding coefficients for a given order and
// writes them to |encoding_coeffs|.
//
// @param ambisonic_order Ambisonic order of the encoded sound source.
// @param source_direction Direction of a sound source in spherical
// coordinates.
// @param source_spread_deg Encoded sound source angular spread in degrees.
// @param encoding_coeffs Pointer to a vector of Ambisonic encoding
// coefficients.
void GetEncodingCoeffs(int ambisonic_order,
const SphericalAngle& source_direction,
float source_spread_deg,
std::vector<float>* encoding_coeffs) const;
private:
// Computes a lookup table of encoding coefficients for one quadrant of the
// sphere.
void ComputeEncoderTable();
// Computes a table of spherical harmonics symmetry information for all
// cartesian axes. Value of 1 indicates that the current spherical harmonic is
// symmetric with respect to the current axis. Value of -1 indicates that the
// current spherical harmonic is anti-symmetric with respect to the current
// axis.
void ComputeSymmetriesTable();
// Returns the unnormalized spherical harmonic coefficient:
// Y_degree^order(azimuth, elevation).
//
// @param alp_value Associated Legendre polynomial for the given degree and
// order evaluated at sin elevation angle: P_degree^order(sin(elevation)).
// @param order Order of the Associated Legendre polynomial.
// @param azimuth_rad Azimuth angle in radians.
// @return Unnormalized spherical harmonic coefficient.
float UnnormalizedSphericalHarmonic(float alp_value, int order,
float azimuth_rad);
// Ambisonic order.
const int max_ambisonic_order_;
// Maximum number of coefficients to be stored in the lookup table equal to
// the number of Ambisonic channels for |max_ambisonic_order_| - 1. This is
// because we do not need to store the coefficient for the first spherical
// harmonic coefficient as it is always 1.
const size_t max_num_coeffs_in_table_;
// Lookup table for storing Ambisonic encoding coefficients for one quadrant
// of the sphere.
std::vector<float> encoder_table_;
// Lookup table for storing information about spherical harmonic symmetries.
std::vector<float> symmetries_table_;
};
} // namespace vraudio
#endif // RESONANCE_AUDIO_AMBISONICS_AMBISONIC_LOOKUP_TABLE_H_
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