Reload image/thumbnail mode when working directory changes

[karlch]

Following from the discussion in #127, the idea to load the images of a new directory immediately in image/thumbnail mode after the working directory was changed came up. Ideally this would:

• Clear the filelist if the new directory contains no images.
• Load the new images into image and thumbnail mode in async to keep the library responsive.
• Focus the image which is selected in the library in both image and thumbnail mode. If the library focus is on a directory, the first image should be a safe fallback.

Implementing this without performance hit is a bit tricky, a first naive diff (attached later for reference) leads to rather bad performance. We would also have to take care how to handle cases like opening only parts of a directory in image mode, e.g. all marks in a tag. Certainly requires more careful thinking and planning, any help or idea is very welcome.

diff --git a/vimiv/api/__init__.py b/vimiv/api/__init__.py
index af3a563..b592d1b 100644
--- a/vimiv/api/__init__.py
+++ b/vimiv/api/__init__.py
@@ -68,12 +68,11 @@ def open(paths: Iterable[str]) -> None:  # pylint: disable=redefined-builtin
     """
     images, directories = files.supported(paths)
     if images:
-        working_directory.handler.chdir(os.path.dirname(images[0]))
         signals.load_images.emit(images)
-        mode = modes.IMAGE
+        working_directory.handler.chdir(os.path.dirname(images[0]))
+        modes.IMAGE.enter()
     elif directories:
         working_directory.handler.chdir(directories[0])
-        mode = modes.LIBRARY
+        modes.LIBRARY.enter()
     else:
         raise commands.CommandError("No valid paths")
-    mode.enter()
diff --git a/vimiv/gui/image.py b/vimiv/gui/image.py
index f7e9e36..cb28f67 100644
--- a/vimiv/gui/image.py
+++ b/vimiv/gui/image.py
@@ -293,8 +293,9 @@ class ScrollableImage(KeyHandler, QGraphicsView):
     def resizeEvent(self, event):
         """Rescale the child image and update statusbar on resize event."""
         super().resizeEvent(event)
-        self.scale(self._scale)
-        api.status.update()  # Zoom level changes
+        if self.scene().items():
+            self.scale(self._scale)
+            api.status.update()  # Zoom level changes
 
     def mousePressEvent(self, event):
         """Update mouse press event to start panning on left button."""
diff --git a/vimiv/imutils/_file_handler.py b/vimiv/imutils/_file_handler.py
index 2162daa..2141b9f 100644
--- a/vimiv/imutils/_file_handler.py
+++ b/vimiv/imutils/_file_handler.py
@@ -172,6 +172,7 @@ class ImageFileHandler(QObject):
     def _init_manipulate(self):
         self.manipulate = immanipulate.Manipulator(self)
 
+    @utils.asyncfunc()
     def _load(self, path: str, reload_only: bool):
         """Load proper displayable QWidget for a path.
 
diff --git a/vimiv/imutils/filelist.py b/vimiv/imutils/filelist.py
index b35458e..9579c27 100644
--- a/vimiv/imutils/filelist.py
+++ b/vimiv/imutils/filelist.py
@@ -134,6 +134,7 @@ class SignalHandler(QObject):
 
         api.signals.load_images.connect(self._on_load_images)
         api.working_directory.handler.images_changed.connect(self._on_images_changed)
+        api.working_directory.handler.loaded.connect(self._on_directory_loaded)
 
     @pyqtSlot(list)
     def _on_load_images(self, paths: List[str]):
@@ -147,8 +148,11 @@ class SignalHandler(QObject):
         Args:
             paths: List of paths to load into filelist.
         """
-        if not paths:
-            _logger.debug("Image filelist: no paths to load")
+        if paths == _paths:
+            _logger.debug("Image filelist: nothing new load")
+        elif not paths:
+            _logger.debug("Image filelist: no paths to load, clearing")
+            api.signals.all_images_cleared.emit()
         elif len(paths) == 1:
             _logger.debug("Image filelist: loading single path %s", paths[0])
             _load_single(*paths)
@@ -156,6 +160,10 @@ class SignalHandler(QObject):
             _logger.debug("Image filelist: loading %d paths", len(paths))
             _load_paths(paths, paths[0])
 
+    @pyqtSlot(list, list)
+    def _on_directory_loaded(self, images: List[str], _directories: List[str]):
+        self._on_load_images(images)
+
     @pyqtSlot(int, list, api.modes.Mode, bool)
     def _on_new_search(
         self, index: int, _matches: List[str], mode: api.modes.Mode, incremental: bool

[karlch]

An interesting mid-ground proposed in #694 by @mcp292 could be to allow --open-selected for :scroll left and :scroll right as well, in this case loading the directory.