Added the watcher class to UI

fury/ui/core.py

@@ -3,6 +3,7 @@
 __all__ = ["Rectangle2D", "Disk2D", "TextBlock2D"]
 
 import abc
+from fury.ui.helpers import Watcher
 from warnings import warn
 
 import numpy as np
@@ -83,6 +84,7 @@ def __init__(self, position=(0, 0)):
         self._callbacks = []
 
         self._setup()  # Setup needed actors and sub UI components.
+        self.watcher = Watcher(self)
         self.position = position
 
         self.left_button_state = "released"

fury/ui/helpers.py

@@ -55,3 +55,93 @@ def clip_overflow(textblock, width, side='right'):
             if side == 'left':
                 textblock.message = textblock.message[::-1]
             return textblock.message
+
+
+class Watcher:
+    """Class to monitor a UI element in runtime
+
+    Attributes
+    ----------
+    instance: :class: `UI`
+        UI element instance
+    show_m: :class: `ShowManager`
+        Show Manager
+    is_running: bool
+        Current running state of the watcher
+    i_ren: :class: `CustomInteractorStyle`
+        CustomInteractorStyle
+    """
+
+    def __init__(self, object):
+        """Initialize the watcher class
+
+        Parameters
+        ----------
+        object: :class: `UI`
+            Instance of the UI element
+        """
+        self.instance = object
+        self.show_m = None
+        self.i_ren = None
+        self.attr = None
+        self.original_attr = None
+        self.updated_attr = None
+        self.is_running = False
+        self.callback = None
+
+    def start(self, delay, show_m, attr):
+        """Start the watcher
+
+        Parameters
+        ----------
+        delay: int
+            delay between each update call
+        show_m: :class: `window.ShowManager`
+            show manager
+        attr: str
+            attribute to watch
+        """
+        self.show_m = show_m
+        self.attr = attr
+        self.i_ren = self.show_m.scene.GetRenderWindow()\
+            .GetInteractor().GetInteractorStyle()
+
+        if hasattr(self.instance, self.attr):
+            self.original_attr = getattr(self.instance, attr)
+
+            if type(self.original_attr) == np.array:
+                self.original_attr = self.original_attr.tolist()
+        else:
+            raise(AttributeError(
+                f'{self.instance} has no attribute {self.attr}')
+            )
+
+        if delay > 0:
+            self.id_timer = self.show_m\
+                .add_timer_callback(True, delay, self.update)
+        else:
+            self.id_observer = self.i_ren.AddObserver('RenderEvent',
+                                                      self.update)
+
+        self.is_running = True
+
+    def stop(self):
+        """Stop the watcher
+        """
+        if self.id_timer:
+            self.show_m.destroy_timer(self.id_timer)
+
+        if self.id_observer:
+            self.i_ren.RemoveObserver(self.id_observer)
+
+        self.is_running = False
+
+    def update(self, _obj, _evt):
+        """ Update the instance of UI element.
+        """
+        self.updated_attr = getattr(self.instance, self.attr)
+
+        if self.original_attr != self.updated_attr:
+            self.callback(self.i_ren, _obj, self.instance)
+            self.original_attr = self.updated_attr
+            self.i_ren.force_render()