Datatable extend background (#1946)

* Extending DataTable widget horizontally

* Fading background of extended DataTable rows

* Updating DataTable snapshots

* Update CHANGELOG.md

---------

Co-authored-by: Will McGugan <willmcgugan@gmail.com>

CHANGELOG.md

@@ -7,13 +7,14 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [0.14.0] - Unreleased
 
-### Changes
+### Changed
 
 - Breaking change: There is now only `post_message` to post events, which is non-async, `post_message_no_wait` was dropped. https://github.com/Textualize/textual/pull/1940
 - Breaking change: The Timer class now has just one method to stop it, `Timer.stop` which is non sync https://github.com/Textualize/textual/pull/1940
 - Breaking change: Messages don't require a `sender` in their constructor https://github.com/Textualize/textual/pull/1940
 - Many messages have grown a `control` property which returns the control they relate to. https://github.com/Textualize/textual/pull/1940
 - Dropped `time` attribute from Messages https://github.com/Textualize/textual/pull/1940
+- Updated styling to make it clear DataTable grows horizontally https://github.com/Textualize/textual/pull/1946
 - Changed the `Checkbox` character due to issues with Windows Terminal and Windows 10 https://github.com/Textualize/textual/issues/1934
 - Changed the `RadioButton` character due to issues with Windows Terminal and Windows 10 and 11 https://github.com/Textualize/textual/issues/1934
 

src/textual/widgets/_data_table.py

@@ -21,6 +21,7 @@ from .._segment_tools import line_crop
 from .._two_way_dict import TwoWayDict
 from .._types import SegmentLines
 from ..binding import Binding, BindingType
+from ..color import Color
 from ..coordinate import Coordinate
 from ..geometry import Region, Size, Spacing, clamp
 from ..message import Message
@@ -880,6 +881,9 @@ class DataTable(ScrollView, Generic[CellType], can_focus=True):
         self._clear_caches()
         self.refresh()
 
+    def on_resize(self, event: events.Resize) -> None:
+        self._update_count += 1
+
     def watch_show_cursor(self, show_cursor: bool) -> None:
         self._clear_caches()
         if show_cursor and self.cursor_type != "none":
@@ -1682,6 +1686,25 @@ class DataTable(ScrollView, Generic[CellType], can_focus=True):
             )[line_no]
             scrollable_row.append(cell_lines)
 
+        # Extending the styling out horizontally to fill the container
+        widget_width = self.size.width
+        table_width = (
+            sum(
+                column.render_width
+                for column in self.ordered_columns[self.fixed_columns :]
+            )
+            + self._row_label_column_width
+        )
+        remaining_space = max(0, widget_width - table_width)
+        background_color = self.background_colors[1]
+        faded_color = Color.from_rich_color(row_style.bgcolor).blend(
+            background_color, factor=0.25
+        )
+        faded_style = Style.from_color(
+            color=row_style.color, bgcolor=faded_color.rich_color
+        )
+        scrollable_row.append([Segment(" " * remaining_space, faded_style)])
+
         row_pair = (fixed_row, scrollable_row)
         self._row_render_cache[cache_key] = row_pair
         return row_pair