rework WaiterOverlay with @vvalls.

* register to ResizeWidget event
* remove text from constructor
* move background to 'semi transparent'
* if the wiget is a PlotWidget prefer center it to the `getWidgetHandle` instead of the plot itself

src/silx/gui/utils/waiteroverlay.py

@@ -2,25 +2,36 @@
 from typing import Optional
 from silx.gui.widgets.WaitingPushButton import WaitingPushButton
 from silx.gui import qt
+from silx.gui.plot import PlotWidget
 
 
-class WaiterOverlay:
-    def __init__(self, underlying_widget: qt.QWidget, text: Optional[str]=None) -> None:
+class WaiterOverlay(qt.QObject):
+    def __init__(self, underlying_widget: qt.QWidget) -> None:
         """
         :param qt.QWidget underlying_widget: widget on top of which we want to displat the "processing/waiting wheel"
         :param str waiting_text: text to apply near the processing wheel
         """
+        super().__init__()
+
+        # TO be checked with thomas
+        if isinstance(underlying_widget, PlotWidget):
+            underlying_widget = underlying_widget.getWidgetHandle()
+
         if not isinstance(underlying_widget, qt.QWidget):
-            raise TypeError
+            raise TypeError(f"underlying_widget is expected to be an instance of QWidget. {type(underlying_widget)} provided.")
         self._baseWidget = weakref.ref(underlying_widget)
         self._waitingButton = WaitingPushButton(
             parent=underlying_widget,
-            text=text,
         )
         self._waitingButton.setDown(True)
         self._waitingButton.setVisible(False)
-        self._waitingButton.setStyleSheet("QPushButton { background-color: transparent; border: 0px }")
-        self.resize()
+        self._waitingButton.setStyleSheet("QPushButton { background-color: rgba(150, 150, 150, 40); border: 0px; border-radius: 10px; }")
+        self._resize()
+        # register to resize event
+        underlying_widget.installEventFilter(self)
+
+    def setText(self, text: str):
+        self._waitingButton.setText(text)
 
     def getBaseWidget(self) -> Optional[qt.QWidget]:
         return self._baseWidget()
@@ -29,8 +40,7 @@ def setWaiting(self, activate=True):
         self._waitingButton.setWaiting(activate)
         self._waitingButton.setVisible(activate)
 
-    def resize(self):
-        # should be called by the widget when resized to keep displaying it in the middle
+    def _resize(self):
         parent = self.getBaseWidget()
         if parent is None:
             return
@@ -40,3 +50,8 @@ def resize(self):
         position = (position - size) / 2
         rect = qt.QRect(qt.QPoint(position.width(), position.height()), size)
         self._waitingButton.setGeometry(rect)
+
+    def eventFilter(self, watched: qt.QWidget, event: qt.QEvent):
+        if event.type() == qt.QEvent.Resize:
+            self._resize()
+        return super().eventFilter(watched, event)