[examples] Add an audio particle generator

examples/Advanced/AudioParticles/AudioParticles.cpp

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+#include "AudioParticles.hpp"
+
+#include <score/tools/RecursiveWatch.hpp>
+
+#include <QDirIterator>
+namespace ao
+{
+void AudioParticles::prepare(halp::setup info)
+{
+  this->rate = info.rate;
+  // Initialization, this method will be called with buffer size, etc.
+  m_sounds.clear();
+  m_sounds.reserve(1000);
+
+  score::for_all_files(inputs.folder.value, [this](std::string_view v) {
+    if(!v.ends_with(".wav"))
+      return;
+
+    const QString& path = QString::fromUtf8(v.data(), v.size());
+
+    auto dec = Media::AudioDecoder::decode_synchronous(path, this->rate);
+    if(!dec)
+      return;
+
+    m_sounds.push_back(std::move(dec->second));
+  });
+}
+
+std::optional<int>
+frame_in_interval(int start_frame, int end_frame, double rate, double freq)
+{
+  if(rate <= 0.)
+    return std::nullopt;
+
+  int64_t start_ns = 1e9 * start_frame / rate;
+  int64_t end_ns = 1e9 * end_frame / rate;
+  int64_t itv_ns = 1e9 / freq;
+  auto start_div = std::div(start_ns, itv_ns);
+  auto end_div = std::div(end_ns, itv_ns);
+  if(end_div.quot > start_div.quot)
+  {
+    return 1;
+  }
+  return std::nullopt;
+}
+void AudioParticles::operator()(const halp::tick_musical& t)
+{
+  if(this->outputs.audio.channels != this->inputs.channels.value)
+  {
+    this->outputs.audio.request_channels(this->inputs.channels.value);
+    return;
+  }
+
+  if(m_sounds.empty())
+    return;
+
+  // FIXME range is not respected
+
+  if(inputs.frequency > 0.)
+    // Trigger new sounds
+    if(frame_in_interval(
+           t.position_in_frames, t.position_in_frames + t.frames, rate,
+           1. / (1. - inputs.frequency)))
+    {
+      if((1. - inputs.density) < std::exponential_distribution<float>()(m_rng))
+        m_playheads.push_back(Playhead{
+            0, uint16_t(unsigned(rand()) % m_sounds.size()),
+            uint16_t(unsigned(rand()) % this->outputs.audio.channels)});
+    }
+
+  for(auto& playhead : m_playheads)
+  {
+    SCORE_ASSERT(m_sounds.size() > playhead.index);
+    auto& sound = m_sounds[playhead.index];
+    int sound_frames = sound[0].size();
+
+    SCORE_ASSERT(outputs.audio.channels > playhead.channel);
+    auto channel = outputs.audio.channel(playhead.channel, t.frames);
+
+    if(sound_frames - playhead.frame > t.frames)
+      for(int i = playhead.frame; i < playhead.frame + t.frames; i++)
+        channel[i - playhead.frame] += sound[0][i];
+    else
+    {
+      for(int i = playhead.frame; i < sound_frames; i++)
+        channel[i - playhead.frame] += sound[0][i];
+    }
+    playhead.frame += t.frames;
+  }
+
+  ossia::remove_erase_if(m_playheads, [this](const auto& playhead) {
+    auto& sound = m_sounds[playhead.index];
+    return playhead.frame >= sound[0].size();
+  });
+}
+}

examples/Advanced/AudioParticles/AudioParticles.hpp

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+#pragma once
+#include <Media/AudioDecoder.hpp>
+#include <halp/audio.hpp>
+#include <halp/controls.hpp>
+#include <halp/mappers.hpp>
+#include <halp/meta.hpp>
+#include <rnd/random.hpp>
+
+#include <QFile>
+namespace ao
+{
+class AudioParticles
+{
+public:
+  halp_meta(name, "Audio particles")
+  halp_meta(category, "Audio/Generator")
+  halp_meta(c_name, "avnd_audio_particles")
+  halp_meta(uuid, "e7f2b091-0de0-49cd-a581-d4087d901fbb")
+
+  struct ins
+  {
+    halp::lineedit<"Folder", ""> folder;
+    halp::spinbox_i32<"Channels", halp::range{.min = 0., .max = 128, .init = 16}>
+        channels;
+    struct : halp::time_chooser<"Frequency", halp::range{0.001, 30., 0.2}>
+    {
+      using mapper = halp::log_mapper<std::ratio<95, 100>>;
+    } frequency;
+    halp::knob_f32<"Density", halp::range{0.001, 1., 0.7}> density;
+  } inputs;
+
+  struct
+  {
+    halp::variable_audio_bus<"Output", double> audio;
+  } outputs;
+
+  using setup = halp::setup;
+  void prepare(halp::setup info);
+
+  // Do our processing for N samples
+  using tick = halp::tick_musical;
+
+  // Defined in the .cpp
+  void operator()(const halp::tick_musical& t);
+
+  std::vector<Media::audio_array> m_sounds;
+
+  struct Playhead
+  {
+    int frame{};
+    uint16_t index{};
+    uint16_t channel{};
+  };
+
+  std::vector<Playhead> m_playheads;
+  double rate{};
+  std::random_device m_rdev;
+  rnd::pcg m_rng{m_rdev};
+};
+
+}