1 /* 2 * Copyright 2022 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 package org.hyphonate.megaaudio.player.sources; 17 18 /** 19 * An AudioSourceProvider for multi-channel sine waves with control over which 20 * channels have audio data and which channels have silence. 21 */ 22 public class SparseChannelAudioSource extends WaveTableSource { 23 /** 24 * The number of SAMPLES in the Sin Wave table. 25 * This is plenty of samples for a clear sine wave. 26 * the + 1 is to avoid special handling of the interpolation on the last sample. 27 */ 28 static final int WAVETABLE_LENGTH = 2049; 29 30 int mChannelsMask; 31 SparseChannelAudioSource(int mask)32 public SparseChannelAudioSource(int mask) { 33 super(); 34 float[] waveTbl = new float[WAVETABLE_LENGTH]; 35 WaveTableSource.genSinWave(waveTbl); 36 37 setWaveTable(waveTbl); 38 39 mChannelsMask = mask; 40 } 41 channelNumToMask(int chanNum)42 private int channelNumToMask(int chanNum) { 43 if (chanNum <= 0) { 44 return 0; 45 } 46 return 1 << (chanNum - 1); 47 } 48 49 @Override pull(float[] buffer, int numFrames, int numChans)50 public int pull(float[] buffer, int numFrames, int numChans) { 51 final float phaseIncr = mFreq * mFNInverse; 52 int outIndex = 0; 53 for (int frameIndex = 0; frameIndex < numFrames; frameIndex++) { 54 // 'mod' back into the waveTable 55 while (mSrcPhase >= (float) mNumWaveTblSamples) { 56 mSrcPhase -= (float) mNumWaveTblSamples; 57 } 58 59 // linear-interpolate 60 int srcIndex = (int) mSrcPhase; 61 float delta0 = mSrcPhase - (float) srcIndex; 62 float delta1 = 1.0f - delta0; 63 float value = ((mWaveTbl[srcIndex] * delta0) + (mWaveTbl[srcIndex + 1] * delta1)); 64 65 // Put the same value in all channels. 66 // This is inefficient and should be pulled out of this loop 67 for (int chanIndex = 0; chanIndex < numChans; chanIndex++) { 68 if ((mChannelsMask & (1 << chanIndex)) != 0) { 69 buffer[outIndex++] = value; 70 } else { 71 buffer[outIndex++] = 0.0f; 72 } 73 } 74 75 mSrcPhase += phaseIncr; 76 } 77 78 return numFrames; 79 } 80 81 } 82