Merge pull request #4315 from Textualize/ping-pong-fix

fix for flicker

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Fixed
 
 - Fixed a crash in `TextArea` when undoing an edit to a selection the selection was made backwards https://github.com/Textualize/textual/issues/4301
+- Fixed issue with flickering scrollbars https://github.com/Textualize/textual/pull/4315
 - Fix progress bar ETA not updating when setting `total` reactive https://github.com/Textualize/textual/pull/4316
 
 ### Changed 

src/textual/screen.py

@@ -38,6 +38,7 @@
 from .css.parse import parse_selectors
 from .css.query import NoMatches, QueryType
 from .dom import DOMNode
+from .errors import NoWidget
 from .geometry import Offset, Region, Size
 from .reactive import Reactive
 from .renderables.background_screen import BackgroundScreen
@@ -54,7 +55,6 @@
     from .command import Provider
 
     # Unused & ignored imports are needed for the docs to link to these objects:
-    from .errors import NoWidget  # type: ignore  # noqa: F401
     from .message_pump import MessagePump
 
 # Screen updates will be batched so that they don't happen more often than 60 times per second:

src/textual/scroll_view.py

@@ -89,6 +89,7 @@ def _size_updated(
             or virtual_size != self.virtual_size
             or container_size != self.container_size
         ):
+            self._scrollbar_changes.clear()
             self._size = size
             virtual_size = self.virtual_size
             self._container_size = size - self.styles.gutter.totals

src/textual/signal.py

@@ -88,4 +88,6 @@ def publish(self) -> None:
                     try:
                         callback()
                     except Exception as error:
-                        log.error(f"error publishing signal to {node} ignored; {error}")
+                        log.error(
+                            f"error publishing signal to {node} ignored (callback={callback}); {error}"
+                        )

src/textual/widget.py

@@ -361,14 +361,15 @@ def __init__(
 
         self._styles_cache = StylesCache()
         self._rich_style_cache: dict[str, tuple[Style, Style]] = {}
-        self._stabilize_scrollbar: tuple[Size, str, str] | None = None
-        """Used to prevent scrollbar logic getting stuck in an infinite loop."""
 
         self._tooltip: RenderableType | None = None
         """The tooltip content."""
         self._absolute_offset: Offset | None = None
         """Force an absolute offset for the widget (used by tooltips)."""
 
+        self._scrollbar_changes: set[tuple[bool, bool]] = set()
+        """Used to stabilize scrollbars."""
+
         super().__init__(
             name=name,
             id=id,
@@ -799,7 +800,6 @@ def _arrange(self, size: Size) -> DockArrangeResult:
     def _clear_arrangement_cache(self) -> None:
         """Clear arrangement cache, forcing a new arrange operation."""
         self._arrangement_cache.clear()
-        self._stabilize_scrollbar = None
 
     def _get_virtual_dom(self) -> Iterable[Widget]:
         """Get widgets not part of the DOM.
@@ -1437,14 +1437,6 @@ def _refresh_scrollbars(self) -> None:
         overflow_x = styles.overflow_x
         overflow_y = styles.overflow_y
 
-        stabilize_scrollbar = (
-            self.container_size,
-            overflow_x,
-            overflow_y,
-        )
-        if self._stabilize_scrollbar == stabilize_scrollbar:
-            return
-
         width, height = self._container_size
 
         show_horizontal = False
@@ -1463,17 +1455,31 @@ def _refresh_scrollbars(self) -> None:
         elif overflow_y == "auto":
             show_vertical = self.virtual_size.height > height
 
-        # When a single scrollbar is shown, the other dimension changes, so we need to recalculate.
-        if overflow_x == "auto" and show_vertical and not show_horizontal:
-            show_horizontal = self.virtual_size.width > (
-                width - styles.scrollbar_size_vertical
-            )
-        if overflow_y == "auto" and show_horizontal and not show_vertical:
-            show_vertical = self.virtual_size.height > (
-                height - styles.scrollbar_size_horizontal
-            )
+        _show_horizontal = show_horizontal
+        _show_vertical = show_vertical
 
-        self._stabilize_scrollbar = stabilize_scrollbar
+        if not (
+            overflow_x == "auto"
+            and overflow_y == "auto"
+            and (show_horizontal, show_vertical) in self._scrollbar_changes
+        ):
+            # When a single scrollbar is shown, the other dimension changes, so we need to recalculate.
+            if overflow_x == "auto" and show_vertical and not show_horizontal:
+                show_horizontal = self.virtual_size.width > (
+                    width - styles.scrollbar_size_vertical
+                )
+            if overflow_y == "auto" and show_horizontal and not show_vertical:
+                show_vertical = self.virtual_size.height > (
+                    height - styles.scrollbar_size_horizontal
+                )
+
+        if (
+            self.show_horizontal_scrollbar != show_horizontal
+            or self.show_vertical_scrollbar != show_vertical
+        ):
+            self._scrollbar_changes.add((_show_horizontal, _show_vertical))
+        else:
+            self._scrollbar_changes.clear()
 
         self.show_horizontal_scrollbar = show_horizontal
         self.show_vertical_scrollbar = show_vertical
@@ -3322,7 +3328,6 @@ def refresh(
             return self
         if layout:
             self._layout_required = True
-            self._stabilize_scrollbar = None
             for ancestor in self.ancestors:
                 if not isinstance(ancestor, Widget):
                     break

src/textual/widgets/_sparkline.py

@@ -66,7 +66,7 @@ def __init__(
 
         Args:
             data: The initial data to populate the sparkline with.
-            summary_function: Summarises bar values into a single value used to
+            summary_function: Summarizes bar values into a single value used to
                 represent each bar.
             name: The name of the widget.
             id: The ID of the widget in the DOM.