viewer: allow temporarily suspending the auto-cache

While the auto-cache will always default to on, there are cases where the
user may not want the viewer to barrel ahead caching something (footage
viewer for instance or if the user is making a lot of changes in a short
amount of time).

app/widget/viewer/viewer.cpp

@@ -58,7 +58,8 @@ ViewerWidget::ViewerWidget(QWidget *parent) :
   time_changed_from_timer_(false),
   prequeuing_(false),
   busy_(false),
-  our_cache_background_task_(nullptr)
+  our_cache_background_task_(nullptr),
+  autocache_(true)
 {
   // Set up main layout
   QVBoxLayout* layout = new QVBoxLayout(this);
@@ -114,7 +115,7 @@ ViewerWidget::ViewerWidget(QWidget *parent) :
   renderer_->SetRenderMode(RenderMode::kOffline);
 
   // Setup cache wait timer (waits a few seconds of inactivity before caching)
-  cache_wait_timer_.setInterval(250);
+  cache_wait_timer_.setInterval(Config::Current()["AutoCacheInterval"].toInt());
   cache_wait_timer_.setSingleShot(true);
   connect(&cache_wait_timer_, &QTimer::timeout, this, &ViewerWidget::StartBackgroundCaching);
 
@@ -369,6 +370,18 @@ void ViewerWidget::ForceUpdate()
   UpdateTextureFromNode(GetTime());
 }
 
+void ViewerWidget::SetAutoCacheEnabled(bool e)
+{
+  autocache_ = e;
+
+  if (autocache_) {
+    StartBackgroundCaching();
+  } else if (cache_background_task_ == our_cache_background_task_) {
+    StopAllBackgroundCacheTasks(false);
+    cache_background_task_ = nullptr;
+  }
+}
+
 void ViewerWidget::SetGizmos(Node *node)
 {
   display_widget_->SetTimeTarget(GetConnectedNode());
@@ -865,10 +878,10 @@ void ViewerWidget::StartBackgroundCaching()
   }
 #endif
 
-  if (GetConnectedNode()
+  if (autocache_
+      && GetConnectedNode()
       && (GetConnectedNode()->video_frame_cache()->HasInvalidatedRanges()
-          || GetConnectedNode()->audio_playback_cache()->HasInvalidatedRanges())
-      && Config::Current()["AutoCache"].toBool()) {
+          || GetConnectedNode()->audio_playback_cache()->HasInvalidatedRanges())) {
     if (cache_background_task_ || busy_viewers_) {
 
       // Something else is caching right now, we don't want to do multiple at once so we'll check
@@ -987,6 +1000,16 @@ void ViewerWidget::ShowContextMenu(const QPoint &pos)
 
   menu.addSeparator();
 
+  {
+    // Auto-cache
+    QAction* autocache_action = menu.addAction(tr("Auto-Cache"));
+    autocache_action->setCheckable(true);
+    autocache_action->setChecked(autocache_);
+    connect(autocache_action, &QAction::triggered, this, &ViewerWidget::SetAutoCacheEnabled);
+  }
+
+  menu.addSeparator();
+
   {
     // Safe Margins
     Menu* safe_margin_menu = new Menu(tr("Safe Margins"), &menu);