text alignment

src/textual/_segment_tools.py

@@ -231,8 +231,6 @@ def blank_lines(count: int) -> list[list[Segment]]:
     if top_blank_lines:
         yield from blank_lines(top_blank_lines)
 
-    horizontal_excess_space = max(0, width - shape_width)
-
     if horizontal == "left":
         for cell_length, line in zip(line_lengths, lines):
             if cell_length == width:
@@ -241,7 +239,7 @@ def blank_lines(count: int) -> list[list[Segment]]:
                 yield line_pad(line, 0, width - cell_length, style)
 
     elif horizontal == "center":
-        left_space = horizontal_excess_space // 2
+        left_space = max(0, width - shape_width) // 2
         for cell_length, line in zip(line_lengths, lines):
             if cell_length == width:
                 yield line

src/textual/content.py

@@ -11,7 +11,6 @@
 from __future__ import annotations
 
 import re
-from itertools import zip_longest
 from operator import itemgetter
 from typing import Callable, Iterable, NamedTuple, Sequence
 
@@ -73,12 +72,10 @@ def _justify_lines(
                     spaces[len(spaces) - index - 1] += 1
                     num_spaces += 1
                     index = (index + 1) % len(spaces)
-            tokens: list[Content] = []
-            for index, (word, next_word) in enumerate(zip_longest(words, words[1:])):
-                if index < len(spaces):
-                    tokens.append(word.extend_right(spaces[index]))
-                else:
-                    tokens.append(word)
+            tokens = [
+                word.extend_right(spaces[index]) if index < len(spaces) else word
+                for index, word in enumerate(words)
+            ]
             new_lines[line_index] = Content("").join(tokens)
 
         return new_lines

src/textual/strip.py

@@ -17,11 +17,13 @@
 from rich.segment import Segment
 from rich.style import Style, StyleType
 
-from textual._segment_tools import index_to_cell_position
+from textual._segment_tools import index_to_cell_position, line_pad
 from textual.cache import FIFOCache
 from textual.color import Color
 from textual.constants import DEBUG
+from textual.css.types import AlignHorizontal, AlignVertical
 from textual.filter import LineFilter
+from textual.geometry import Size
 
 
 def get_line_length(segments: Iterable[Segment]) -> int:
@@ -157,6 +159,87 @@ def from_lines(
         """
         return [cls(segments, cell_length) for segments in lines]
 
+    @classmethod
+    def align(
+        cls,
+        strips: list[Strip],
+        style: Style,
+        size: Size,
+        horizontal: AlignHorizontal,
+        vertical: AlignVertical,
+    ) -> Iterable[Strip]:
+        if not strips:
+            return
+        width, height = size
+        line_lengths = [strip.cell_length for strip in strips]
+        shape_width = max(line_lengths)
+        shape_height = len(line_lengths)
+
+        def blank_lines(count: int) -> Iterable[Strip]:
+            """Create blank lines.
+
+            Args:
+                count: Desired number of blank lines.
+
+            Returns:
+                An iterable of blank lines.
+            """
+            blank = cls([Segment(" " * width, style)], width)
+            for _ in range(count):
+                yield blank
+
+        top_blank_lines = bottom_blank_lines = 0
+        vertical_excess_space = max(0, height - shape_height)
+
+        if vertical == "top":
+            bottom_blank_lines = vertical_excess_space
+        elif vertical == "middle":
+            top_blank_lines = vertical_excess_space // 2
+            bottom_blank_lines = vertical_excess_space - top_blank_lines
+        elif vertical == "bottom":
+            top_blank_lines = vertical_excess_space
+
+        if top_blank_lines:
+            yield from blank_lines(top_blank_lines)
+
+        if horizontal == "left":
+            for strip in strips:
+                if strip.cell_length == width:
+                    yield strip
+                else:
+                    yield Strip(
+                        line_pad(strip._segments, 0, width - strip.cell_length, style),
+                        width,
+                    )
+        elif horizontal == "center":
+            left_space = max(0, width - shape_width) // 2
+            for strip in strips:
+                if strip.cell_length == width:
+                    yield strip
+                else:
+                    yield Strip(
+                        line_pad(
+                            strip._segments,
+                            left_space,
+                            width - strip.cell_length - left_space,
+                            style,
+                        ),
+                        width,
+                    )
+
+        elif horizontal == "right":
+            for strip in strips:
+                if strip.cell_length == width:
+                    yield strip
+                else:
+                    yield cls(
+                        line_pad(strip._segments, width - strip.cell_length, 0, style),
+                        width,
+                    )
+
+        if bottom_blank_lines:
+            yield from blank_lines(bottom_blank_lines)
+
     def index_to_cell_position(self, index: int) -> int:
         """Given a character index, return the cell position of that character.
         This is the sum of the cell lengths of all the characters *before* the character

src/textual/widget.py

@@ -3700,20 +3700,26 @@ def _render_content(self) -> None:
         """Render all lines."""
         width, height = self.size
         renderable = self.render()
+        styles = self.styles
+        align_horizontal, align_vertical = styles.content_align
 
         visual = textualize(renderable)
         if visual is not None:
-            visual_style = self.visual_style
             strips = visual.render_strips(
                 width,
                 height=height,
                 base_style=self.visual_style,
                 justify=self._get_justify_method() or "left",
             )
-            strips = [
-                strip.adjust_cell_length(width, visual_style.rich_style)
-                for strip in strips
-            ]
+            strips = list(
+                Strip.align(
+                    strips,
+                    _NULL_STYLE,
+                    self.size,
+                    align_horizontal,
+                    align_vertical,
+                )
+            )
 
         else:
             renderable = self.post_render(renderable)
@@ -3732,8 +3738,6 @@ def _render_content(self) -> None:
                 )
             )
 
-            styles = self.styles
-            align_horizontal, align_vertical = styles.content_align
             lines = list(
                 align_lines(
                     lines,