text: /*
    ==============================================================================
  
     This file is part of the JUCE library.
     Copyright (c) 2020 - Raw Material Software Limited
  
     JUCE is an open source library subject to commercial or open-source
     licensing.
  
     The code included in this file is provided under the terms of the ISC license
     http://www.isc.org/downloads/software-support-policy/isc-license. Permission
     To use, copy, modify, and/or distribute this software for any purpose with or
     without fee is hereby granted provided that the above copyright notice and
     this permission notice appear in all copies.
  
     JUCE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY, AND ALL WARRANTIES, WHETHER
     EXPRESSED OR IMPLIED, INCLUDING MERCHANTABILITY AND FITNESS FOR PURPOSE, ARE
     DISCLAIMED.
  
    ==============================================================================
  */
  
  namespace juce
  {
  
  //==============================================================================
  /**
      Used by AudioSource::getNextAudioBlock().
  
      @tags{Audio}
  */
  struct JUCE_API  AudioSourceChannelInfo
  {
      /** Creates an uninitialised AudioSourceChannelInfo. */
      AudioSourceChannelInfo() = default;
  
      /** Creates an AudioSourceChannelInfo. */
      AudioSourceChannelInfo (AudioBuffer<float>* bufferToUse,
                              int startSampleOffset, int numSamplesToUse) noexcept
          : buffer (bufferToUse),
            startSample (startSampleOffset),
            numSamples (numSamplesToUse)
      {
      }
  
      /** Creates an AudioSourceChannelInfo that uses the whole of a buffer.
          Note that the buffer provided must not be deleted while the
          AudioSourceChannelInfo is still using it.
      */
      explicit AudioSourceChannelInfo (AudioBuffer<float>& bufferToUse) noexcept
          : buffer (&bufferToUse),
            startSample (0),
            numSamples (bufferToUse.getNumSamples())
      {
      }
  
      /** The destination buffer to fill with audio data.
  
          When the AudioSource::getNextAudioBlock() method is called, the active section
          of this buffer should be filled with whatever output the source produces.
  
          Only the samples specified by the startSample and numSamples members of this structure
          should be affected by the call.
  
          The contents of the buffer when it is passed to the AudioSource::getNextAudioBlock()
          method can be treated as the input if the source is performing some kind of filter operation,
          but should be cleared if this is not the case - the clearActiveBufferRegion() is
          a handy way of doing this.
  
          The number of channels in the buffer could be anything, so the AudioSource
          must cope with this in whatever way is appropriate for its function.
      */
      AudioBuffer<float>* buffer;
  
      /** The first sample in the buffer from which the callback is expected
          to write data. */
      int startSample;
  
      /** The number of samples in the buffer which the callback is expected to
          fill with data. */
      int numSamples;
  
      /** Convenient method to clear the buffer if the source is not producing any data. */
      void clearActiveBufferRegion() const
      {
          if (buffer != nullptr)
              buffer->clear (startSample, numSamples);
      }
  };
  
  
  //==============================================================================
  /**
      Base class for objects that can produce a continuous stream of audio.
  
      An AudioSource has two states: 'prepared' and 'unprepared'.
  
      When a source needs to be played, it is first put into a 'prepared' state by a call to
      prepareToPlay(), and then repeated calls will be made to its getNextAudioBlock() method to
      process the audio data.
  
      Once playback has finished, the releaseResources() method is called to put the stream
      back into an 'unprepared' state.
  
      @see AudioFormatReaderSource, ResamplingAudioSource
  
      @tags{Audio}
  */
  class JUCE_API  AudioSource
  {
  protected:
      //==============================================================================
      /** Creates an AudioSource. */
      AudioSource() = default;
  
  public:
      /** Destructor. */
      virtual ~AudioSource()      = default;
  
      //==============================================================================
      /** Tells the source to prepare for playing.
  
          An AudioSource has two states: prepared and unprepared.
  
          The prepareToPlay() method is guaranteed to be called at least once on an 'unprepared'
          source to put it into a 'prepared' state before any calls will be made to getNextAudioBlock().
          This callback allows the source to initialise any resources it might need when playing.
  
          Once playback has finished, the releaseResources() method is called to put the stream
          back into an 'unprepared' state.
  
          Note that this method could be called more than once in succession without
          a matching call to releaseResources(), so make sure your code is robust and
          can handle that kind of situation.
  
          @param samplesPerBlockExpected  the number of samples that the source
                                          will be expected to supply each time its
                                          getNextAudioBlock() method is called. This
                                          number may vary slightly, because it will be dependent
                                          on audio hardware callbacks, and these aren't
                                          guaranteed to always use a constant block size, so
                                          the source should be able to cope with small variations.
          @param sampleRate               the sample rate that the output will be used at - this
                                          is needed by sources such as tone generators.
          @see releaseResources, getNextAudioBlock
      */
      virtual void prepareToPlay (int samplesPerBlockExpected,
                                  double sampleRate) = 0;
  
      /** Allows the source to release anything it no longer needs after playback has stopped.
  
          This will be called when the source is no longer going to have its getNextAudioBlock()
          method called, so it should release any spare memory, etc. that it might have
          allocated during the prepareToPlay() call.
  
          Note that there's no guarantee that prepareToPlay() will actually have been called before
          releaseResources(), and it may be called more than once in succession, so make sure your
          code is robust and doesn't make any assumptions about when it will be called.
  
          @see prepareToPlay, getNextAudioBlock
      */
      virtual void releaseResources() = 0;
  
      /** Called repeatedly to fetch subsequent blocks of audio data.
  
          After calling the prepareToPlay() method, this callback will be made each
          time the audio playback hardware (or whatever other destination the audio
          data is going to) needs another block of data.
  
          It will generally be called on a high-priority system thread, or possibly even
          an interrupt, so be careful not to do too much work here, as that will cause
          audio glitches!
  
          @see AudioSourceChannelInfo, prepareToPlay, releaseResources
      */
      virtual void getNextAudioBlock (const AudioSourceChannelInfo& bufferToFill) = 0;
  };
  
  } // namespace juce
  