From 690be62a8ded70d2484598ce5dec9e356d761ff8 Mon Sep 17 00:00:00 2001
From: Tristan Simas <tristan.simas@mail.mcgill.ca>
Date: Fri, 6 Nov 2026 01:20:22 -0500
Subject: [PATCH] refresh_lines repaints a widget's lines without rendering its
 content again

A full refresh() reaches _set_dirty(), which adds the whole widget to _dirty_regions, so
render_line rebuilds the content: right for "the content changed", wrong for an animation
frame that only tints the same lines in render_line. Toad's arrival fades did exactly that,
rebuilding every Markdown block and row of a fading entry each frame (rich Style construction
was 19% of the live main thread). refresh_lines() invalidates and repaints every line from
the content already rendered; _invalidate_lines is the half _set_dirty already did, now
owned once and inherited by both.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 src/textual/widget.py | 36 ++++++++++++++++++++++++++----------
 1 file changed, 26 insertions(+), 10 deletions(-)

diff --git a/src/textual/widget.py b/src/textual/widget.py
index 0e8b0912fe..cd7d1b6fa7 100644
--- a/src/textual/widget.py
+++ b/src/textual/widget.py
@@ -2546,16 +2546,19 @@ def _set_dirty(self, *regions: Region) -> None:
             self._styles_cache.set_dirty(*widget_regions)
         else:
             self._dirty_regions.clear()
-            self._repaint_regions.clear()
-            self._styles_cache.clear()
-            # Invalidation must not measure a lazily invalidated compositor.
-            # Mark the last committed local content bounds; the next geometry
-            # commit dirties its new bounds independently.
-            self._styles_cache.set_dirty(self._size.region.shrink(self.geometry.box_gutter).reset_offset)
-            outer_size = self.outer_size
-            self._dirty_regions.add(outer_size.region)
-            if outer_size:
-                self._repaint_regions.add(outer_size.region)
+            self._invalidate_lines()
+            self._dirty_regions.add(self.outer_size.region)
+
+    def _invalidate_lines(self) -> None:
+        """Every line is painted again on the next frame, from whatever content is rendered."""
+        self._repaint_regions.clear()
+        self._styles_cache.clear()
+        # Invalidation must not measure a lazily invalidated compositor.
+        # Mark the last committed local content bounds; the next geometry
+        # commit dirties its new bounds independently.
+        self._styles_cache.set_dirty(self._size.region.shrink(self.geometry.box_gutter).reset_offset)
+        if outer_size := self.outer_size:
+            self._repaint_regions.add(outer_size.region)
 
     def _exchange_repaint_regions(self) -> Collection[Region]:
         """Get a copy of the regions which need a repaint, and clear internal cache.
@@ -4242,6 +4245,19 @@ def refresh(
         self.check_idle()
         return self
 
+    def refresh_lines(self) -> Self:
+        """Paint every line again from the content already rendered.
+
+        For a change over the lines and not in them: an animation frame tinting the same
+        text. `refresh()` renders the content again; this keeps it and re-runs `render_line`.
+        """
+        if not self._is_mounted:
+            return self.refresh()
+        self._invalidate_lines()
+        self._repaint_required = True
+        self.check_idle()
+        return self
+
     def remove(self) -> AwaitRemove:
         """Remove the Widget from the DOM (effectively deleting it).