From 0a396998f7803e8857f935b28d9f3dd4a38af2be Mon Sep 17 00:00:00 2001
From: Will McGugan <willmcgugan@gmail.com>
Date: Sat, 6 Sep 2025 10:20:20 +0100
Subject: [PATCH 1/9] optimize layout

---
 src/textual/_profile.py         | 15 ++++++++----
 src/textual/layout.py           |  2 ++
 src/textual/layouts/stream.py   | 41 +++++++++++++++++++++++++++++++++
 src/textual/layouts/vertical.py |  3 +++
 src/textual/widget.py           |  2 +-
 5 files changed, 58 insertions(+), 5 deletions(-)

diff --git a/src/textual/_profile.py b/src/textual/_profile.py
index 3e880cf15c..8324db9dee 100644
--- a/src/textual/_profile.py
+++ b/src/textual/_profile.py
@@ -10,10 +10,17 @@
 
 
 @contextlib.contextmanager
-def timer(subject: str = "time") -> Generator[None, None, None]:
-    """print the elapsed time. (only used in debugging)"""
+def timer(subject: str = "time", threshold: float = 0) -> Generator[None, None, None]:
+    """print the elapsed time. (only used in debugging).
+
+    Args:
+        subject: Text shown in log.
+        threshold: Time in second after which the log is written.
+
+    """
     start = perf_counter()
     yield
     elapsed = perf_counter() - start
-    elapsed_ms = elapsed * 1000
-    log(f"{subject} elapsed {elapsed_ms:.4f}ms")
+    if elapsed >= threshold:
+        elapsed_ms = elapsed * 1000
+        log(f"{subject} elapsed {elapsed_ms:.4f}ms")
diff --git a/src/textual/layout.py b/src/textual/layout.py
index fe7ca4335b..fc16b7290e 100644
--- a/src/textual/layout.py
+++ b/src/textual/layout.py
@@ -226,6 +226,7 @@ def arrange(
             An iterable of widget location
         """
 
+    # @timer("get_content_width")
     def get_content_width(self, widget: Widget, container: Size, viewport: Size) -> int:
         """Get the optimal content width by arranging children.
 
@@ -247,6 +248,7 @@ def get_content_width(self, widget: Widget, container: Size, viewport: Size) ->
             width = arrangement.total_region.right
         return width
 
+    # @timer("get_content_height")
     def get_content_height(
         self, widget: Widget, container: Size, viewport: Size, width: int
     ) -> int:
diff --git a/src/textual/layouts/stream.py b/src/textual/layouts/stream.py
index ffae3b58ce..8ef4c9a16e 100644
--- a/src/textual/layouts/stream.py
+++ b/src/textual/layouts/stream.py
@@ -10,6 +10,9 @@
     from textual.widget import Widget
 
 
+from textual._profile import timer
+
+
 class StreamLayout(Layout):
     """A cut down version of the vertical layout.
 
@@ -31,9 +34,11 @@ class StreamLayout(Layout):
 
     name = "stream"
 
+    @timer("arrange STREAM")
     def arrange(
         self, parent: Widget, children: list[Widget], size: Size, greedy: bool = True
     ) -> ArrangeResult:
+        print(parent)
         parent.pre_layout(self)
         if not children:
             return []
@@ -81,3 +86,39 @@ def arrange(
             y += height
 
         return placements
+
+    @timer("STREAM.get_content_width")
+    def get_content_width(self, widget: Widget, container: Size, viewport: Size) -> int:
+        """Get the optimal content width by arranging children.
+
+        Args:
+            widget: The container widget.
+            container: The container size.
+            viewport: The viewport size.
+
+        Returns:
+            Width of the content.
+        """
+        return widget.scrollable_content_region.width
+
+    @timer("STREAM.get_content_height")
+    def get_content_height(
+        self, widget: Widget, container: Size, viewport: Size, width: int
+    ) -> int:
+        """Get the content height.
+
+        Args:
+            widget: The container widget.
+            container: The container size.
+            viewport: The viewport.
+            width: The content width.
+
+        Returns:
+            Content height (in lines).
+        """
+        if widget._nodes:
+            arrangement = widget._arrange(Size(width, 0))
+            height = arrangement.total_region.height
+        else:
+            height = 0
+        return height
diff --git a/src/textual/layouts/vertical.py b/src/textual/layouts/vertical.py
index b229fa6622..ab7261a9ff 100644
--- a/src/textual/layouts/vertical.py
+++ b/src/textual/layouts/vertical.py
@@ -11,12 +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("arrange VERTICAL")
     def arrange(
         self, parent: Widget, children: list[Widget], size: Size, greedy: bool = True
     ) -> ArrangeResult:
diff --git a/src/textual/widget.py b/src/textual/widget.py
index 63ab9664c1..1d272f8c2f 100644
--- a/src/textual/widget.py
+++ b/src/textual/widget.py
@@ -717,10 +717,10 @@ def _cover(self, widget: Widget) -> None:
         self._uncover()
         self._cover_widget = widget
         widget._parent = self
+        widget._start_messages()
         widget._post_register(self.app)
         self.app.stylesheet.apply(widget)
         self.refresh(layout=True)
-        widget._start_messages()
 
     def _uncover(self) -> None:
         """Remove any widget, previously set via [`_cover`][textual.widget.Widget._cover]."""

From fdfac1e878fbcdbce7162df808e845f72051af1a Mon Sep 17 00:00:00 2001
From: Will McGugan <willmcgugan@gmail.com>
Date: Sat, 6 Sep 2025 13:08:26 +0100
Subject: [PATCH 2/9] use app.screen

---
 src/textual/layouts/grid.py | 2 +-
 src/textual/screen.py       | 2 +-
 src/textual/widget.py       | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/textual/layouts/grid.py b/src/textual/layouts/grid.py
index 5aa419b057..432f337148 100644
--- a/src/textual/layouts/grid.py
+++ b/src/textual/layouts/grid.py
@@ -60,7 +60,7 @@ def arrange(
                     table_size_columns -= 1
 
         table_size_rows = styles.grid_size_rows
-        viewport = parent.screen.size
+        viewport = parent.app.size
         keyline_style, _keyline_color = styles.keyline
         offset = (0, 0)
         gutter_spacing: Spacing | None
diff --git a/src/textual/screen.py b/src/textual/screen.py
index 14e11046da..3bec40bbb5 100644
--- a/src/textual/screen.py
+++ b/src/textual/screen.py
@@ -512,7 +512,7 @@ def get_maximize_widgets(maximized: Widget) -> list[Widget]:
                 else self._nodes
             ),
             size,
-            self.screen.size,
+            self.app.size,
             False,
         )
 
diff --git a/src/textual/widget.py b/src/textual/widget.py
index 1d272f8c2f..c1ed53a8f3 100644
--- a/src/textual/widget.py
+++ b/src/textual/widget.py
@@ -1263,7 +1263,7 @@ def _arrange(self, size: Size, optimal: bool = False) -> DockArrangeResult:
             return cached_result
 
         arrangement = self._arrangement_cache[cache_key] = arrange(
-            self, self._nodes, size, self.screen.size, optimal=optimal
+            self, self._nodes, size, self.app.size, optimal=optimal
         )
 
         return arrangement

From 13c993ecb5a0a1e2b250e91dfd90cfdd155a23b0 Mon Sep 17 00:00:00 2001
From: Will McGugan <willmcgugan@gmail.com>
Date: Sat, 6 Sep 2025 13:35:58 +0100
Subject: [PATCH 3/9] optimize screen size

---
 src/textual/screen.py | 7 ++++++-
 src/textual/widget.py | 4 ++--
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/src/textual/screen.py b/src/textual/screen.py
index 3bec40bbb5..f721a3913f 100644
--- a/src/textual/screen.py
+++ b/src/textual/screen.py
@@ -341,6 +341,11 @@ def layers(self) -> tuple[str, ...]:
             extras.append("_tooltips")
         return (*super().layers, *extras)
 
+    @property
+    def size(self) -> Size:
+        """The size of the screen."""
+        return self.app.size - self.styles.gutter.totals
+
     def _watch_focused(self):
         self.refresh_bindings()
 
@@ -512,7 +517,7 @@ def get_maximize_widgets(maximized: Widget) -> list[Widget]:
                 else self._nodes
             ),
             size,
-            self.app.size,
+            self.size,
             False,
         )
 
diff --git a/src/textual/widget.py b/src/textual/widget.py
index c1ed53a8f3..d064eb8b70 100644
--- a/src/textual/widget.py
+++ b/src/textual/widget.py
@@ -605,7 +605,7 @@ def offset(self) -> Offset:
         Returns:
             Relative offset.
         """
-        return self.styles.offset.resolve(self.size, self.app.size)
+        return self.styles.offset.resolve(self.size, self.screen.size)
 
     @offset.setter
     def offset(self, offset: tuple[int, int]) -> None:
@@ -1263,7 +1263,7 @@ def _arrange(self, size: Size, optimal: bool = False) -> DockArrangeResult:
             return cached_result
 
         arrangement = self._arrangement_cache[cache_key] = arrange(
-            self, self._nodes, size, self.app.size, optimal=optimal
+            self, self._nodes, size, self.screen.size, optimal=optimal
         )
 
         return arrangement

From 98899a0cfb3d85e27ce595ca182a6f4cca7e96ac Mon Sep 17 00:00:00 2001
From: Will McGugan <willmcgugan@gmail.com>
Date: Sat, 6 Sep 2025 18:03:05 +0100
Subject: [PATCH 4/9] optimization

---
 src/textual/_arrange.py | 19 ++++++++++---------
 src/textual/widget.py   |  2 +-
 2 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/src/textual/_arrange.py b/src/textual/_arrange.py
index ddab9b185c..bb6bec570e 100644
--- a/src/textual/_arrange.py
+++ b/src/textual/_arrange.py
@@ -31,6 +31,11 @@ def _build_layers(widgets: Iterable[Widget]) -> Mapping[str, Sequence[Widget]]:
     return layers
 
 
+_get_dock = attrgetter("styles.is_docked")
+_get_split = attrgetter("styles.is_split")
+_get_display = attrgetter("display")
+
+
 def arrange(
     widget: Widget,
     children: Sequence[Widget],
@@ -50,22 +55,18 @@ def arrange(
     """
 
     placements: list[WidgetPlacement] = []
-    scroll_spacing = Spacing()
-
-    get_dock = attrgetter("styles.is_docked")
-    get_split = attrgetter("styles.is_split")
-    get_display = attrgetter("styles.display")
-
+    scroll_spacing = NULL_SPACING
     styles = widget.styles
 
     # Widgets which will be displayed
-    display_widgets = [child for child in children if get_display(child) != "none"]
+    # display_widgets = [child for child in children if get_display(child) != "none"]
+    display_widgets = list(filter(_get_display, children))
     # Widgets organized into layers
     layers = _build_layers(display_widgets)
 
     for widgets in layers.values():
         # Partition widgets into split widgets and non-split widgets
-        non_split_widgets, split_widgets = partition(get_split, widgets)
+        non_split_widgets, split_widgets = partition(_get_split, widgets)
         if split_widgets:
             _split_placements, dock_region = _arrange_split_widgets(
                 split_widgets, size, viewport
@@ -78,7 +79,7 @@ def arrange(
 
         # Partition widgets into "layout" widgets (those that appears in the normal 'flow' of the
         # document), and "dock" widgets which are positioned relative to an edge
-        layout_widgets, dock_widgets = partition(get_dock, non_split_widgets)
+        layout_widgets, dock_widgets = partition(_get_dock, non_split_widgets)
 
         # Arrange docked widgets
         if dock_widgets:
diff --git a/src/textual/widget.py b/src/textual/widget.py
index d064eb8b70..403984ec0b 100644
--- a/src/textual/widget.py
+++ b/src/textual/widget.py
@@ -460,7 +460,7 @@ def __init__(
         self._content_height_cache: tuple[object, int] = (None, 0)
 
         self._arrangement_cache: FIFOCache[
-            tuple[Size, int, Widget], DockArrangeResult
+            tuple[Size, int, Widget | None], DockArrangeResult
         ] = FIFOCache(4)
 
         self._styles_cache = StylesCache()

From 9d427840349d9a5e9e1f2a25db44af65f72656b4 Mon Sep 17 00:00:00 2001
From: Will McGugan <willmcgugan@gmail.com>
Date: Sat, 6 Sep 2025 18:23:08 +0100
Subject: [PATCH 5/9] process layout hook

---
 src/textual/_arrange.py |  6 ++++--
 src/textual/widget.py   | 18 +++++++++++++++++-
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/src/textual/_arrange.py b/src/textual/_arrange.py
index bb6bec570e..9b65c9d127 100644
--- a/src/textual/_arrange.py
+++ b/src/textual/_arrange.py
@@ -95,8 +95,10 @@ def arrange(
 
         if layout_widgets:
             # Arrange layout widgets (i.e. not docked)
-            layout_placements = widget.layout.arrange(
-                widget, layout_widgets, dock_region.size, greedy=not optimal
+            layout_placements = widget.process_layout(
+                widget.layout.arrange(
+                    widget, layout_widgets, dock_region.size, greedy=not optimal
+                )
             )
             scroll_spacing = scroll_spacing.grow_maximum(dock_spacing)
             placement_offset = dock_region.offset
diff --git a/src/textual/widget.py b/src/textual/widget.py
index 403984ec0b..ae298fe121 100644
--- a/src/textual/widget.py
+++ b/src/textual/widget.py
@@ -79,7 +79,7 @@
     Spacing,
     clamp,
 )
-from textual.layout import Layout
+from textual.layout import Layout, WidgetPlacement
 from textual.layouts.vertical import VerticalLayout
 from textual.message import Message
 from textual.messages import CallbackType, Prune
@@ -722,6 +722,22 @@ def _cover(self, widget: Widget) -> None:
         self.app.stylesheet.apply(widget)
         self.refresh(layout=True)
 
+    def process_layout(
+        self, placements: list[WidgetPlacement]
+    ) -> list[WidgetPlacement]:
+        """A hook to allow for the manipulation of widget placements before rendering.
+
+        You could use this as a way to modify the positions / margins of widgets if your requirement is
+        not supported in TCSS. In practice, this method is rarely needed!
+
+        Args:
+            placements: A list of [`WidgetPlacement`][textual.layout.WidgetPlacement] objects.
+
+        Returns:
+            A new list of placements.
+        """
+        return placements
+
     def _uncover(self) -> None:
         """Remove any widget, previously set via [`_cover`][textual.widget.Widget._cover]."""
         if self._cover_widget is not None:

From 87e918db4ce6fabf4681cc71fea4a466c5211a34 Mon Sep 17 00:00:00 2001
From: Will McGugan <willmcgugan@gmail.com>
Date: Sat, 6 Sep 2025 18:23:41 +0100
Subject: [PATCH 6/9] changelog

---
 CHANGELOG.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 299c3db889..f23df7a8b6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,10 +11,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 - Eager tasks are now enabled On Python3.12 and above https://github.com/Textualize/textual/pull/6102
 
-
 ### Added
 
 - Added `DOMNode.displayed_and_visible_children` https://github.com/Textualize/textual/pull/6102
+- Added `Widget.process_layout`
 
 ## [6.1.0] - 2025-08-01
 

From 6fd179790ed41fb42a1f364faa737af939c014d4 Mon Sep 17 00:00:00 2001
From: Will McGugan <willmcgugan@gmail.com>
Date: Sat, 6 Sep 2025 18:31:08 +0100
Subject: [PATCH 7/9] remove timers

---
 CHANGELOG.md                      | 2 +-
 src/textual/_arrange.py           | 1 -
 src/textual/layout.py             | 2 --
 src/textual/layouts/grid.py       | 2 +-
 src/textual/layouts/horizontal.py | 2 +-
 src/textual/layouts/stream.py     | 9 +--------
 src/textual/layouts/vertical.py   | 5 +----
 7 files changed, 5 insertions(+), 18 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index f23df7a8b6..4977fcd24d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,7 +14,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Added
 
 - Added `DOMNode.displayed_and_visible_children` https://github.com/Textualize/textual/pull/6102
-- Added `Widget.process_layout`
+- Added `Widget.process_layout` https://github.com/Textualize/textual/pull/6105
 
 ## [6.1.0] - 2025-08-01
 
diff --git a/src/textual/_arrange.py b/src/textual/_arrange.py
index 9b65c9d127..6cdca4af3d 100644
--- a/src/textual/_arrange.py
+++ b/src/textual/_arrange.py
@@ -59,7 +59,6 @@ def arrange(
     styles = widget.styles
 
     # Widgets which will be displayed
-    # display_widgets = [child for child in children if get_display(child) != "none"]
     display_widgets = list(filter(_get_display, children))
     # Widgets organized into layers
     layers = _build_layers(display_widgets)
diff --git a/src/textual/layout.py b/src/textual/layout.py
index fc16b7290e..fe7ca4335b 100644
--- a/src/textual/layout.py
+++ b/src/textual/layout.py
@@ -226,7 +226,6 @@ def arrange(
             An iterable of widget location
         """
 
-    # @timer("get_content_width")
     def get_content_width(self, widget: Widget, container: Size, viewport: Size) -> int:
         """Get the optimal content width by arranging children.
 
@@ -248,7 +247,6 @@ def get_content_width(self, widget: Widget, container: Size, viewport: Size) ->
             width = arrangement.total_region.right
         return width
 
-    # @timer("get_content_height")
     def get_content_height(
         self, widget: Widget, container: Size, viewport: Size, width: int
     ) -> int:
diff --git a/src/textual/layouts/grid.py b/src/textual/layouts/grid.py
index 432f337148..5aa419b057 100644
--- a/src/textual/layouts/grid.py
+++ b/src/textual/layouts/grid.py
@@ -60,7 +60,7 @@ def arrange(
                     table_size_columns -= 1
 
         table_size_rows = styles.grid_size_rows
-        viewport = parent.app.size
+        viewport = parent.screen.size
         keyline_style, _keyline_color = styles.keyline
         offset = (0, 0)
         gutter_spacing: Spacing | None
diff --git a/src/textual/layouts/horizontal.py b/src/textual/layouts/horizontal.py
index c1720173d6..735759bc75 100644
--- a/src/textual/layouts/horizontal.py
+++ b/src/textual/layouts/horizontal.py
@@ -25,7 +25,7 @@ def arrange(
         parent.pre_layout(self)
         placements: list[WidgetPlacement] = []
         add_placement = placements.append
-        viewport = parent.app.size
+        viewport = parent.screen.size
 
         child_styles = [child.styles for child in children]
         box_margins: list[Spacing] = [
diff --git a/src/textual/layouts/stream.py b/src/textual/layouts/stream.py
index 8ef4c9a16e..014198f663 100644
--- a/src/textual/layouts/stream.py
+++ b/src/textual/layouts/stream.py
@@ -10,9 +10,6 @@
     from textual.widget import Widget
 
 
-from textual._profile import timer
-
-
 class StreamLayout(Layout):
     """A cut down version of the vertical layout.
 
@@ -34,15 +31,13 @@ class StreamLayout(Layout):
 
     name = "stream"
 
-    @timer("arrange STREAM")
     def arrange(
         self, parent: Widget, children: list[Widget], size: Size, greedy: bool = True
     ) -> ArrangeResult:
-        print(parent)
         parent.pre_layout(self)
         if not children:
             return []
-        viewport = parent.app.size
+        viewport = parent.screen.size
 
         _Region = Region
         _WidgetPlacement = WidgetPlacement
@@ -87,7 +82,6 @@ def arrange(
 
         return placements
 
-    @timer("STREAM.get_content_width")
     def get_content_width(self, widget: Widget, container: Size, viewport: Size) -> int:
         """Get the optimal content width by arranging children.
 
@@ -101,7 +95,6 @@ def get_content_width(self, widget: Widget, container: Size, viewport: Size) ->
         """
         return widget.scrollable_content_region.width
 
-    @timer("STREAM.get_content_height")
     def get_content_height(
         self, widget: Widget, container: Size, viewport: Size, width: int
     ) -> int:
diff --git a/src/textual/layouts/vertical.py b/src/textual/layouts/vertical.py
index ab7261a9ff..d04e04b4d1 100644
--- a/src/textual/layouts/vertical.py
+++ b/src/textual/layouts/vertical.py
@@ -11,22 +11,19 @@
     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("arrange VERTICAL")
     def arrange(
         self, parent: Widget, children: list[Widget], size: Size, greedy: bool = True
     ) -> ArrangeResult:
         parent.pre_layout(self)
         placements: list[WidgetPlacement] = []
         add_placement = placements.append
-        viewport = parent.app.size
+        viewport = parent.screen.size
 
         child_styles = [child.styles for child in children]
         box_margins: list[Spacing] = [

From 2e2d5d588d1b57d159b052e5bcda44ee48810383 Mon Sep 17 00:00:00 2001
From: Will McGugan <willmcgugan@gmail.com>
Date: Sat, 6 Sep 2025 18:38:27 +0100
Subject: [PATCH 8/9] fix stack error

---
 src/textual/app.py                | 8 ++++++++
 src/textual/layouts/grid.py       | 2 +-
 src/textual/layouts/horizontal.py | 2 +-
 src/textual/layouts/stream.py     | 2 +-
 src/textual/layouts/vertical.py   | 2 +-
 5 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/src/textual/app.py b/src/textual/app.py
index 26c3f818f4..92748d0e7d 100644
--- a/src/textual/app.py
+++ b/src/textual/app.py
@@ -1565,6 +1565,14 @@ def size(self) -> Size:
             width, height = self.console.size
         return Size(width, height)
 
+    @property
+    def viewport_size(self) -> Size:
+        """Get the viewport size (size of the screen)."""
+        try:
+            return self.screen.size
+        except (ScreenStackError, NoScreen):
+            return self.size
+
     def _get_inline_height(self) -> int:
         """Get the inline height (height when in inline mode).
 
diff --git a/src/textual/layouts/grid.py b/src/textual/layouts/grid.py
index 5aa419b057..c6f518360b 100644
--- a/src/textual/layouts/grid.py
+++ b/src/textual/layouts/grid.py
@@ -60,7 +60,7 @@ def arrange(
                     table_size_columns -= 1
 
         table_size_rows = styles.grid_size_rows
-        viewport = parent.screen.size
+        viewport = parent.app.viewport_size
         keyline_style, _keyline_color = styles.keyline
         offset = (0, 0)
         gutter_spacing: Spacing | None
diff --git a/src/textual/layouts/horizontal.py b/src/textual/layouts/horizontal.py
index 735759bc75..fdead10c1f 100644
--- a/src/textual/layouts/horizontal.py
+++ b/src/textual/layouts/horizontal.py
@@ -25,7 +25,7 @@ def arrange(
         parent.pre_layout(self)
         placements: list[WidgetPlacement] = []
         add_placement = placements.append
-        viewport = parent.screen.size
+        viewport = parent.app.viewport_size
 
         child_styles = [child.styles for child in children]
         box_margins: list[Spacing] = [
diff --git a/src/textual/layouts/stream.py b/src/textual/layouts/stream.py
index 014198f663..9665f408f6 100644
--- a/src/textual/layouts/stream.py
+++ b/src/textual/layouts/stream.py
@@ -37,7 +37,7 @@ def arrange(
         parent.pre_layout(self)
         if not children:
             return []
-        viewport = parent.screen.size
+        viewport = parent.app.viewport_size
 
         _Region = Region
         _WidgetPlacement = WidgetPlacement
diff --git a/src/textual/layouts/vertical.py b/src/textual/layouts/vertical.py
index d04e04b4d1..4f68449417 100644
--- a/src/textual/layouts/vertical.py
+++ b/src/textual/layouts/vertical.py
@@ -23,7 +23,7 @@ def arrange(
         parent.pre_layout(self)
         placements: list[WidgetPlacement] = []
         add_placement = placements.append
-        viewport = parent.screen.size
+        viewport = parent.app.viewport_size
 
         child_styles = [child.styles for child in children]
         box_margins: list[Spacing] = [

From 037790a7b9c5918241e6d0e435a7c5b3b19c2325 Mon Sep 17 00:00:00 2001
From: Will McGugan <willmcgugan@gmail.com>
Date: Sun, 7 Sep 2025 08:27:02 +0100
Subject: [PATCH 9/9] changelog

---
 CHANGELOG.md | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4977fcd24d..2531e0c14f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 - Added `DOMNode.displayed_and_visible_children` https://github.com/Textualize/textual/pull/6102
 - Added `Widget.process_layout` https://github.com/Textualize/textual/pull/6105
+- Added `App.viewport_size` https://github.com/Textualize/textual/pull/6105
+- Added `Screen.size` https://github.com/Textualize/textual/pull/6105
 
 ## [6.1.0] - 2025-08-01