Regularly check if graphics is modified when visible on screen (#10596)

In case one cannot rely on QFileSystemWatcher.

see https://www.mail-archive.com/lyx-devel@lists.lyx.org/msg199112.html

src/graphics/GraphicsCacheItem.cpp

@@ -99,7 +99,7 @@ public:
 	/// The document filename this graphic item belongs to
 	FileName const & doc_file_;
 	///
-	FileMonitorPtr monitor_;
+	ActiveFileMonitorPtr monitor_;
 
 	/// Is the file compressed?
 	bool zipped_;
@@ -179,6 +179,14 @@ bool CacheItem::monitoring() const
 }
 
 
+void CacheItem::checkModifiedAsync() const
+{
+	if (!pimpl_->monitor_)
+		return;
+	pimpl_->monitor_->checkModifiedAsync();
+}
+
+
 Image const * CacheItem::image() const
 {
 	return pimpl_->image_.get();
@@ -214,7 +222,7 @@ void CacheItem::Impl::startMonitor()
 {
 	if (monitor_)
 		return;
-	monitor_ = FileSystemWatcher::monitor(filename_);
+	monitor_ = FileSystemWatcher::activeMonitor(filename_);
 	monitor_->connect([=](){ startLoading(); });
 }
 

src/graphics/GraphicsCacheItem.h

@@ -66,6 +66,8 @@ public:
 	void startMonitoring() const;
 	///
 	bool monitoring() const;
+	/// perform a modification check asynchronously
+	void checkModifiedAsync() const;
 
 	/** Get the image associated with filename().
 	 *  If the image is not yet loaded, returns 0.

src/graphics/GraphicsLoader.cpp

@@ -328,6 +328,15 @@ bool Loader::monitoring() const
 }
 
 
+void Loader::checkModifiedAsync() const
+{
+	if (!pimpl_->cached_item_)
+		return;
+
+	pimpl_->cached_item_->checkModifiedAsync();
+}
+
+
 FileName const & Loader::filename() const
 {
 	static FileName const empty;

src/graphics/GraphicsLoader.h

@@ -81,6 +81,8 @@ public:
 	void startMonitoring() const;
 	///
 	bool monitoring() const;
+	///
+	void checkModifiedAsync() const;
 
 	/// How far have we got in loading the image?
 	ImageStatus status() const;

src/insets/RenderGraphic.cpp

@@ -142,6 +142,7 @@ void RenderGraphic::metrics(MetricsInfo & mi, Dimension & dim) const
 			loader_.startLoading();
 		if (!loader_.monitoring())
 			loader_.startMonitoring();
+		loader_.checkModifiedAsync();
 	}
 
 	bool const image_ready = displayGraphic(params_) && readyToDisplay(loader_);