ENH: Wait for image data to render before progressing

If image data is provided on initialization the viewer is not marked as ready
until the data has been rendered. If set_image or set_label_image are called
the viewer is again marked as "not ready" until the new data is rendered.

itkwidgets/_initialization_params.py

@@ -92,3 +92,8 @@ def build_init_data(input_data):
             raise RuntimeError(f"Could not process the viewer {input_type}")
         input_data[render_type.value] = result
     return input_data
+
+
+def defer_for_data_render(init_data):
+    deferred_keys = ['image', 'labelImage']
+    return any([k in init_data.keys() for k in deferred_keys])

itkwidgets/cell_watcher.py

@@ -38,17 +38,22 @@ def viewer_objects(self):
         return list(self.data.keys())
 
     def add_viewer(self, view):
-        self._data[view] = {'name': None, 'status': False}
+        self.data[view] = {'name': None, 'status': False}
 
     def set_name(self, view, name):
         if view not in self.data.keys():
             self.add_viewer(view)
-        self._data[view]['name'] = name
+        self.data[view]['name'] = name
 
     def update_viewer_status(self, view, status):
         if view not in self.data.keys():
             self.add_viewer(view)
-        self._data[view]['status'] = status
+        self.data[view]['status'] = status
+
+    def viewer_ready(self, view):
+        if viewer := self.data.get(view):
+            return viewer['status']
+        return False
 
 
 class CellWatcher(object):
@@ -94,6 +99,9 @@ def update_viewer_status(self, view, status):
             # Might be ready now, try again
             self.create_task(self.execute_next_request)
 
+    def viewer_ready(self, view):
+        return self.viewers.viewer_ready(view)
+
     def _task_cleanup(self, task):
         global background_tasks
         try:

itkwidgets/viewer.py

@@ -12,6 +12,7 @@
     build_config,
     parse_input_data,
     build_init_data,
+    defer_for_data_render,
 )
 from .cell_watcher import CellWatcher
 from .imjoy import register_itkwasm_imjoy_codecs
@@ -82,8 +83,12 @@ async def run(self, ctx):
             if ENVIRONMENT is not Env.JUPYTERLITE:
                 # Create the initial screenshot
                 await self.create_screenshot()
-                # Once the viewer has been created any queued requests can be run
-                CellWatcher().update_viewer_status(self.parent, True)
+                itk_viewer.registerEventListener(
+                    'renderedImageAssigned', self.update_viewer_status
+                )
+                if not defer_for_data_render(self.init_data):
+                    # Once the viewer has been created any queued requests can be run
+                    CellWatcher().update_viewer_status(self.parent, True)
 
             # Wait and then update the screenshot in case rendered level changed
             await asyncio.sleep(10)
@@ -118,6 +123,10 @@ def update_screenshot(self, base64_image):
             ''')
         self.img.display(html)
 
+    def update_viewer_status(self, name):
+        if not CellWatcher().viewer_ready(self.parent):
+            CellWatcher().update_viewer_status(self.parent, True)
+
 
 class Viewer:
     """Pythonic Viewer class."""
@@ -201,6 +210,7 @@ def set_image(self, image: Image, name: str = 'Image'):
                 svc.set_label_or_image('image')
             else:
                 self.viewer_rpc.itk_viewer.setImage(image, name)
+                CellWatcher().update_viewer_status(self.name, False)
         elif render_type is RenderType.POINT_SET:
             image = _get_viewer_point_set(image)
             self.viewer_rpc.itk_viewer.setPointSets(image)
@@ -318,6 +328,7 @@ def compare_images(self, fixed_image: Union[str, Image], moving_image: Union[str
         if swap_image_order is not None:
             options['swapImageOrder'] = swap_image_order
         self.viewer_rpc.itk_viewer.compareImages(fixed_name, moving_name, options)
+        CellWatcher().update_viewer_status(self.name, False)
 
     @fetch_value
     def set_label_image(self, label_image: Image):
@@ -331,6 +342,7 @@ def set_label_image(self, label_image: Image):
                 svc.set_label_or_image('label_image')
             else:
                 self.viewer_rpc.itk_viewer.setLabelImage(label_image)
+                CellWatcher().update_viewer_status(self.name, False)
         elif render_type is RenderType.POINT_SET:
             label_image = _get_viewer_point_set(label_image)
             self.viewer_rpc.itk_viewer.setPointSets(label_image)