faster layout in stream

Author: willmcgugan

src/textual/_arrange.py

@@ -53,7 +53,6 @@ def arrange(
     Returns:
         Widget arrangement information.
     """
-    print("ARRANGE", widget)
     placements: list[WidgetPlacement] = []
     scroll_spacing = NULL_SPACING
     styles = widget.styles

src/textual/layouts/stream.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+from itertools import zip_longest
 from typing import TYPE_CHECKING
 
 from textual.geometry import NULL_OFFSET, Region, Size
@@ -30,6 +31,9 @@ class StreamLayout(Layout):
 
     name = "stream"
 
+    def __init__(self) -> None:
+        self._cache: dict[object, list[WidgetPlacement]] = {}
+
     def arrange(
         self, parent: Widget, children: list[Widget], size: Size, greedy: bool = True
     ) -> ArrangeResult:
@@ -38,6 +42,10 @@ def arrange(
             return []
         viewport = parent.app.viewport_size
 
+        cache_key = (size, viewport)
+        previous_results = self._cache.get(cache_key, None) or []
+        layout_widgets = parent.screen._layout_widgets.get(parent, [])
+
         _Region = Region
         _WidgetPlacement = WidgetPlacement
 
@@ -48,7 +56,18 @@ def arrange(
         previous_margin = first_child_styles.margin.top
         null_offset = NULL_OFFSET
 
-        for widget in children:
+        pre_populate = bool(previous_results and layout_widgets)
+        for widget, placement in zip_longest(children, previous_results):
+            if pre_populate and placement is not None and widget == placement.widget:
+                if widget in layout_widgets:
+                    pre_populate = False
+                else:
+                    placements.append(placement)
+                    y = placement.region.bottom
+                    continue
+            if widget is None:
+                break
+
             styles = widget.styles._base_styles
             margin = styles.margin
             gutter_width, gutter_height = styles.gutter.totals
@@ -85,6 +104,7 @@ def arrange(
             )
             y += height
 
+        self._cache[cache_key] = placements
         return placements
 
     def get_content_width(self, widget: Widget, container: Size, viewport: Size) -> int:

src/textual/layouts/vertical.py

@@ -11,19 +11,15 @@
     from textual.geometry import Spacing
     from textual.widget import Widget
 
-from textual._profile import timer
-
 
 class VerticalLayout(Layout):
     """Used to layout Widgets vertically on screen, from top to bottom."""
 
     name = "vertical"
 
-    @timer("Vertical.arrange")
     def arrange(
         self, parent: Widget, children: list[Widget], size: Size, greedy: bool = True
     ) -> ArrangeResult:
-        print(parent, size, greedy, len(children))
         parent.pre_layout(self)
         placements: list[WidgetPlacement] = []
         add_placement = placements.append

src/textual/reactive.py

@@ -362,8 +362,6 @@ def _set(self, obj: Reactable, value: ReactiveType, always: bool = False) -> Non
 
             # Refresh according to descriptor flags
             if self._layout or self._repaint or self._recompose:
-                if self._layout:
-                    print(self, "layout", obj)
                 obj.refresh(
                     repaint=self._repaint,
                     layout=self._layout,

src/textual/screen.py

@@ -321,7 +321,7 @@ def __init__(
         self._css_update_count = -1
         """Track updates to CSS."""
 
-        self._layout_widgets: set[Widget] = set()
+        self._layout_widgets: dict[DOMNode, set[Widget]] = {}
         """Widgets whose layout may have changed."""
 
     @property
@@ -1353,8 +1353,22 @@ async def _on_update(self, message: messages.Update) -> None:
     async def _on_layout(self, message: messages.Layout) -> None:
         message.stop()
         message.prevent_default()
-        if message.widget not in self._layout_widgets:
-            self._layout_widgets.add(message.widget)
+
+        layout_required = True
+        widget: DOMNode = message.widget
+        for ancestor in message.widget.ancestors:
+            if not isinstance(ancestor, Widget):
+                break
+            if ancestor not in self._layout_widgets:
+                self._layout_widgets[ancestor] = set()
+            # assert isinstance(widget, Widget)
+            self._layout_widgets[ancestor].add(widget)
+            layout_required = True
+            if not ancestor.styles.auto_dimensions:
+                break
+            widget = ancestor
+
+        if layout_required:
             self._layout_required = True
             self.check_idle()