Faster layout

src/textual/_arrange.py

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

src/textual/_compositor.py

@@ -1248,8 +1248,7 @@ def update_widgets(self, widgets: set[Widget]) -> None:
             offset = region.offset
             intersection = clip.intersection
             for dirty_region in widget._exchange_repaint_regions():
-                update_region = intersection(dirty_region.translate(offset))
-                if update_region:
+                if update_region := intersection(dirty_region.translate(offset)):
                     add_region(update_region)
 
         self._dirty_regions.update(regions)

src/textual/_styles_cache.py

@@ -104,7 +104,6 @@ def render_widget(self, widget: Widget, crop: Region) -> list[Strip]:
         Returns:
             Rendered lines.
         """
-
         border_title = widget._border_title
         border_subtitle = widget._border_subtitle
 

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 +31,11 @@ class StreamLayout(Layout):
 
     name = "stream"
 
+    def __init__(self) -> None:
+        self._cached_placements: list[WidgetPlacement] | None = None
+        self._cached_width = 0
+        super().__init__()
+
     def arrange(
         self, parent: Widget, children: list[Widget], size: Size, greedy: bool = True
     ) -> ArrangeResult:
@@ -38,6 +44,12 @@ def arrange(
             return []
         viewport = parent.app.viewport_size
 
+        if size.width != self._cached_width:
+            self._cached_placements = None
+        previous_results = self._cached_placements or []
+
+        layout_widgets = parent.screen._layout_widgets.get(parent, [])
+
         _Region = Region
         _WidgetPlacement = WidgetPlacement
 
@@ -48,7 +60,20 @@ 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 is placement.widget:
+                if widget in layout_widgets:
+                    pre_populate = False
+                else:
+                    placements.append(placement)
+                    y = placement.region.bottom
+                    styles = widget.styles._base_styles
+                    previous_margin = styles.margin.bottom
+                    continue
+            if widget is None:
+                break
+
             styles = widget.styles._base_styles
             margin = styles.margin
             gutter_width, gutter_height = styles.gutter.totals
@@ -85,6 +110,8 @@ def arrange(
             )
             y += height
 
+        self._cached_width = size.width
+        self._cached_placements = placements
         return placements
 
     def get_content_width(self, widget: Widget, container: Size, viewport: Size) -> int:

src/textual/messages.py

@@ -52,6 +52,10 @@ def can_replace(self, message: Message) -> bool:
 class Layout(Message, verbose=True):
     """Sent by Textual when a layout is required."""
 
+    def __init__(self, widget: Widget) -> None:
+        super().__init__()
+        self.widget = widget
+
     def can_replace(self, message: Message) -> bool:
         return isinstance(message, Layout)
 

src/textual/screen.py

@@ -321,6 +321,9 @@ def __init__(
         self._css_update_count = -1
         """Track updates to CSS."""
 
+        self._layout_widgets: dict[DOMNode, set[Widget]] = {}
+        """Widgets whose layout may have changed."""
+
     @property
     def is_modal(self) -> bool:
         """Is the screen modal?"""
@@ -486,11 +489,12 @@ def active_bindings(self) -> dict[str, ActiveBinding]:
 
         return bindings_map
 
-    def arrange(self, size: Size) -> DockArrangeResult:
+    def arrange(self, size: Size, _optimal: bool = False) -> DockArrangeResult:
         """Arrange children.
 
         Args:
             size: Size of container.
+            optimal: Ignored on screen.
 
         Returns:
             Widget locations.
@@ -1270,7 +1274,7 @@ def _refresh_layout(self, size: Size | None = None, scroll: bool = False) -> Non
         ResizeEvent = events.Resize
 
         try:
-            if scroll:
+            if scroll and not self._layout_widgets:
                 exposed_widgets = self._compositor.reflow_visible(self, size)
                 if exposed_widgets:
                     layers = self._compositor.layers
@@ -1295,6 +1299,7 @@ def _refresh_layout(self, size: Size | None = None, scroll: bool = False) -> Non
 
             else:
                 hidden, shown, resized = self._compositor.reflow(self, size)
+                self._layout_widgets.clear()
                 Hide = events.Hide
                 Show = events.Show
 
@@ -1348,8 +1353,24 @@ async def _on_update(self, message: messages.Update) -> None:
     async def _on_layout(self, message: messages.Layout) -> None:
         message.stop()
         message.prevent_default()
-        self._layout_required = True
-        self.check_idle()
+
+        layout_required = False
+        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()
+            if widget not in self._layout_widgets:
+                self._layout_widgets[ancestor].add(widget)
+                layout_required = True
+            if not ancestor.styles.auto_dimensions:
+                break
+            widget = ancestor
+
+        if layout_required and not self._layout_required:
+            self._layout_required = True
+            self.check_idle()
 
     async def _on_update_scroll(self, message: messages.UpdateScroll) -> None:
         message.stop()

src/textual/widget.py

@@ -60,7 +60,7 @@
 from textual.actions import SkipAction
 from textual.await_remove import AwaitRemove
 from textual.box_model import BoxModel
-from textual.cache import FIFOCache
+from textual.cache import FIFOCache, LRUCache
 from textual.color import Color
 from textual.compose import compose
 from textual.content import Content, ContentType
@@ -427,6 +427,7 @@ def __init__(
         self._size = _null_size
         self._container_size = _null_size
         self._layout_required = False
+        self._layout_updates = 0
         self._repaint_required = False
         self._scroll_required = False
         self._recompose_required = False
@@ -455,6 +456,8 @@ def __init__(
         # Regions which need to be transferred from cache to screen
         self._repaint_regions: set[Region] = set()
 
+        self._box_model_cache: LRUCache[object, BoxModel] = LRUCache(16)
+
         # Cache the auto content dimensions
         self._content_width_cache: tuple[object, int] = (None, 0)
         self._content_height_cache: tuple[object, int] = (None, 0)
@@ -1642,6 +1645,19 @@ def _get_box_model(
         Returns:
             The size and margin for this widget.
         """
+        cache_key = (
+            container,
+            viewport,
+            width_fraction,
+            height_fraction,
+            constrain_width,
+            greedy,
+            self._layout_updates,
+            self.styles._cache_key,
+        )
+        if cached_box_model := self._box_model_cache.get(cache_key):
+            return cached_box_model
+
         styles = self.styles
         is_border_box = styles.box_sizing == "border-box"
         gutter = styles.gutter  # Padding plus border
@@ -1750,6 +1766,7 @@ def _get_box_model(
         model = BoxModel(
             content_width + gutter.width, content_height + gutter.height, margin
         )
+        self._box_model_cache[cache_key] = model
         return model
 
     def get_content_width(self, container: Size, viewport: Size) -> int:
@@ -3610,7 +3627,7 @@ def scroll_visible(
         """
         parent = self.parent
         if isinstance(parent, Widget):
-            if self.region:
+            if self._size:
                 self.screen.scroll_to_widget(
                     self,
                     animate=animate,
@@ -4200,14 +4217,9 @@ def refresh(
         Returns:
             The `Widget` instance.
         """
-        if layout:
+        if layout and not self._layout_required:
             self._layout_required = True
-            for ancestor in self.ancestors:
-                if not isinstance(ancestor, Widget):
-                    break
-                ancestor._clear_arrangement_cache()
-                if not ancestor.styles.auto_dimensions:
-                    break
+            self._layout_updates += 1
 
         if recompose:
             self._recompose_required = True
@@ -4422,7 +4434,14 @@ def _check_refresh(self) -> None:
                         screen.post_message(messages.Update(self))
                 if self._layout_required:
                     self._layout_required = False
-                    screen.post_message(messages.Layout())
+                    for ancestor in self.ancestors:
+                        if not isinstance(ancestor, Widget):
+                            break
+                        ancestor._clear_arrangement_cache()
+                        ancestor._layout_updates += 1
+                        if not ancestor.styles.auto_dimensions:
+                            break
+                    screen.post_message(messages.Layout(self))
 
     def focus(self, scroll_visible: bool = True) -> Self:
         """Give focus to this widget.

src/textual/widgets/_button.py

@@ -228,7 +228,7 @@ class Button(Widget, can_focus=True):
 
     BINDINGS = [Binding("enter", "press", "Press button", show=False)]
 
-    label: reactive[ContentText] = reactive[ContentText](Content.empty)
+    label: reactive[ContentText] = reactive[ContentText](Content.empty())
     """The text label that appears within the button."""
 
     variant = reactive("default", init=False)
@@ -293,11 +293,12 @@ def __init__(
         if label is None:
             label = self.css_identifier_styled
 
-        self.label = Content.from_text(label)
         self.variant = variant
-        self.action = action
-        self.compact = compact
         self.flat = flat
+        self.compact = compact
+        self.set_reactive(Button.label, Content.from_text(label))
+
+        self.action = action
         self.active_effect_duration = 0.2
         """Amount of time in seconds the button 'press' animation lasts."""
 

tests/snapshot_tests/test_snapshots.py

@@ -807,7 +807,9 @@ def test_remove_with_auto_height(snap_compare):
 
 
 def test_auto_table(snap_compare):
-    assert snap_compare(SNAPSHOT_APPS_DIR / "auto-table.py", terminal_size=(120, 40))
+    assert snap_compare(
+        SNAPSHOT_APPS_DIR / "auto-table.py", terminal_size=(120, 40), press=["wait:100"]
+    )
 
 
 def test_table_markup(snap_compare):

tests/test_box_model.py

@@ -133,7 +133,6 @@ def get_content_height(self, container: Size, parent: Size, width: int) -> int:
     styles.margin = 2
 
     box_model = widget._get_box_model(Size(60, 20), Size(80, 24), one, one)
-    print(box_model)
     assert box_model == BoxModel(Fraction(56), Fraction(10), Spacing(2, 2, 2, 2))
 
     styles.margin = 1, 2, 3, 4