audiowaveformview: multithreaded waveform rendering

2020-11-30 08:18:11 +11:00
parent f48c8b552b
commit b39565cff4
4 changed files with 158 additions and 70 deletions
@@ -36,6 +36,8 @@ AudioWaveformView::AudioWaveformView(QWidget *parent) :
 {
  setAutoFillBackground(true);
  setBackgroundRole(QPalette::Base);
+
+  cached_waveform_.resize(QThread::idealThreadCount());
 }

 void AudioWaveformView::SetViewer(AudioPlaybackCache *playback)
@@ -73,66 +75,44 @@ void AudioWaveformView::paintEvent(QPaintEvent *event)
    return;
  }

-  if (cached_size_ != size()
-      || cached_scale_ != GetScale()
-      || cached_scroll_ != GetScroll()) {
-
-    cached_waveform_ = QPixmap(size());
-    cached_waveform_.fill(Qt::transparent);
-
-    QIODevice* fs = playback_->CreatePlaybackDevice();
-
-    if (fs->open(QFile::ReadOnly)) {
-
-      QPainter wave_painter(&cached_waveform_);
-
-      // FIXME: Hardcoded color
-      wave_painter.setPen(QColor(64, 255, 160));
-
-      int drew = 0;
-
-      fs->seek(params.samples_to_bytes(ScreenToUnitRounded(0)));
-
-      for (int x=0; x<width() && !fs->atEnd(); x++) {
-        int samples_len = ScreenToUnitRounded(x+1) - ScreenToUnitRounded(x);
-        int max_read_size = params.samples_to_bytes(samples_len);
-
-        QByteArray read_buffer = fs->read(max_read_size);
-
-        // Detect whether we've reached EOF and recalculate sample count if so
-        if (read_buffer.size() < max_read_size) {
-          samples_len = params.bytes_to_samples(read_buffer.size());
-        }
-
-        QVector<AudioVisualWaveform::SamplePerChannel> samples = AudioVisualWaveform::SumSamples(reinterpret_cast<const float*>(read_buffer.constData()),
-                                                                                       samples_len,
-                                                                                       params.channel_count());
-
-        for (int i=0;i<params.channel_count();i++) {
-          AudioVisualWaveform::DrawSample(&wave_painter, samples, x, 0, height());
-
-          drew++;
-        }
-      }
-
-      cached_size_ = size();
-      cached_scale_ = GetScale();
-      cached_scroll_ = GetScroll();
-
-      fs->close();
-
-    }
-
-    delete fs;
-  }
-
  QPainter p(this);

  // Draw in/out points
  DrawTimelinePoints(&p);

-  // Draw cached waveform pixmap
-  p.drawPixmap(0, 0, cached_waveform_);
+  CachedWaveformInfo wanted_info = {size(), GetScale(), GetScroll(), params};
+
+  for (int i=0; i<cached_waveform_.size(); i++) {
+    ActiveCache& cache = cached_waveform_[i];
+
+    int slice_start = width()/cached_waveform_.size() * i;
+    int slice_end = width()/cached_waveform_.size() * (i+1);
+
+    if (cache.info == wanted_info) {
+
+      // Draw pixmap
+      p.drawPixmap(slice_start, 0, cache.pixmap);
+
+    } else if (cache.caching_info != wanted_info) {
+
+      // Pixmap is obsolete, will need to draw again
+
+      // Delete any existing watcher so we don't receive the signal
+      delete cache.watcher;
+
+      // Queue a new background cache operation
+      cache.caching_info = wanted_info;
+      cache.watcher = new QFutureWatcher<QPixmap>();
+      connect(cache.watcher, &QFutureWatcher<QPixmap>::finished, this, &AudioWaveformView::BackgroundCacheFinished);
+      cache.watcher->setFuture(QtConcurrent::run(this,
+                                                 &AudioWaveformView::DrawWaveform,
+                                                 playback_->CreatePlaybackDevice(),
+                                                 wanted_info,
+                                                 slice_start,
+                                                 slice_end));
+
+    }
+  }

  // Draw playhead
  p.setPen(PLAYHEAD_COLOR);
@@ -141,6 +121,53 @@ void AudioWaveformView::paintEvent(QPaintEvent *event)
  p.drawLine(playhead_x, 0, playhead_x, height());
 }

+QPixmap AudioWaveformView::DrawWaveform(QIODevice* fs, CachedWaveformInfo info, int slice_start, int slice_end) const
+{
+  QPixmap pixmap(slice_end - slice_start, info.size.height());
+  pixmap.fill(Qt::transparent);
+
+  if (fs->open(QFile::ReadOnly)) {
+
+    QPainter wave_painter(&pixmap);
+
+    // FIXME: Hardcoded color
+    wave_painter.setPen(QColor(64, 255, 160));
+
+    int drew = 0;
+
+    fs->seek(info.params.samples_to_bytes(ScreenToUnitRounded(slice_start)));
+
+    for (int x=slice_start; x<slice_end && !fs->atEnd(); x++) {
+      int samples_len = ScreenToUnitRounded(x+1) - ScreenToUnitRounded(x);
+      int max_read_size = info.params.samples_to_bytes(samples_len);
+
+      QByteArray read_buffer = fs->read(max_read_size);
+
+      // Detect whether we've reached EOF and recalculate sample count if so
+      if (read_buffer.size() < max_read_size) {
+        samples_len = info.params.bytes_to_samples(read_buffer.size());
+      }
+
+      QVector<AudioVisualWaveform::SamplePerChannel> samples = AudioVisualWaveform::SumSamples(reinterpret_cast<const float*>(read_buffer.constData()),
+                                                                                               samples_len,
+                                                                                               info.params.channel_count());
+
+      for (int i=0;i<info.params.channel_count();i++) {
+        AudioVisualWaveform::DrawSample(&wave_painter, samples, x - slice_start, 0, info.size.height());
+
+        drew++;
+      }
+    }
+
+    fs->close();
+
+  }
+
+  delete fs;
+
+  return pixmap;
+}
+
 void AudioWaveformView::BackendParamsChanged()
 {
  SetTimebase(playback_->GetParameters().time_base());
@@ -148,8 +175,40 @@ void AudioWaveformView::BackendParamsChanged()

 void AudioWaveformView::ForceUpdate()
 {
-  cached_size_ = QSize();
+  // Forces the cache to invalidate
+  for (int i=0; i<cached_waveform_.size(); i++) {
+    cached_waveform_[i].info.size = QSize();
+  }
+
  update();
 }

+void AudioWaveformView::BackgroundCacheFinished()
+{
+  // Retrieve sender
+  QFutureWatcher<QPixmap>* watcher = static_cast<QFutureWatcher<QPixmap>*>(sender());
+
+  // Determine index
+  int index = -1;
+  for (int i=0; i<cached_waveform_.size(); i++) {
+    if (cached_waveform_.at(i).watcher == watcher) {
+      index = i;
+      break;
+    }
+  }
+
+  if (index > -1) {
+    // Store generated pixmap
+    cached_waveform_[index].info = cached_waveform_[index].caching_info;
+    cached_waveform_[index].pixmap = watcher->result();
+    cached_waveform_[index].watcher = nullptr;
+
+    // Update with new pixmap
+    update();
+  }
+
+  // Clean up
+  delete watcher;
+}
+
 }