From 7d4db0f811d49d9364024a600c77ea42ab34d5d2 Mon Sep 17 00:00:00 2001
From: Will McGugan <willmcgugan@gmail.com>
Date: Sat, 1 Oct 2022 21:09:38 +0100
Subject: [PATCH] optimizations for compositor

---
 src/textual/_compositor.py | 22 ++++++++++++----------
 src/textual/screen.py      | 22 +++++++++++-----------
 2 files changed, 23 insertions(+), 21 deletions(-)

diff --git a/src/textual/_compositor.py b/src/textual/_compositor.py
index bc64632a3..b00466f6a 100644
--- a/src/textual/_compositor.py
+++ b/src/textual/_compositor.py
@@ -482,7 +482,7 @@ class Compositor:
     @property
     def layers_visible(self) -> dict[int, list[tuple[Widget, Region, Region]]]:
         """Visible widgets and regions in layers order."""
-
+        screen_height = self.size.height
         if self._layers_visible is None:
             layers_visible: dict[int, list[tuple[Widget, Region, Region]]]
             layers_visible = {y: [] for y in range(self.size.height)}
@@ -490,28 +490,30 @@ class Compositor:
                 y: layer.append for y, layer in layers_visible.items()
             }
             intersection = Region.intersection
+            _range = range
             for widget, (region, _, clip, _, _, _) in self.layers:
-                cropped_region = intersection(region, clip)
-                _x, region_y, _width, height = cropped_region
-                widget_location = (widget, cropped_region, region)
-                for y in range(region_y, region_y + height):
-                    layers_visible_appends[y](widget_location)
+                _x, y, _width, height = region
+                if -height <= y < screen_height:
+                    cropped_region = intersection(region, clip)
+                    _x, region_y, _width, region_height = cropped_region
+                    if region_height:
+                        widget_location = (widget, cropped_region, region)
+                        for y in _range(region_y, region_y + region_height):
+                            layers_visible_appends[y](widget_location)
             self._layers_visible = layers_visible
         return self._layers_visible
 
-    def __iter__(self) -> Iterator[tuple[Widget, Region, Region, Size, Size]]:
+    def __iter__(self) -> Iterator[tuple[Widget, Region, Size, Size]]:
         """Iterate map with information regarding each widget and is position
 
         Yields:
             Iterator[tuple[Widget, Region, Region, Size, Size]]: Iterates a tuple of
-                Widget, clip region, region, virtual size, and container size.
+                Widget, region, virtual size, and container size.
         """
         layers = self.layers
-        intersection = Region.intersection
         for widget, (region, _order, clip, virtual_size, container_size, _) in layers:
             yield (
                 widget,
-                intersection(region, clip),
                 region,
                 virtual_size,
                 container_size,
diff --git a/src/textual/screen.py b/src/textual/screen.py
index 8db9b91d7..bf96c5082 100644
--- a/src/textual/screen.py
+++ b/src/textual/screen.py
@@ -216,22 +216,22 @@ class Screen(Widget):
 
             # We want to send a resize event to widgets that were just added or change since last layout
             send_resize = shown | resized
+            ResizeEvent = events.Resize
 
-            for (
-                widget,
-                _region,
-                unclipped_region,
+            _size_updated = Widget._size_updated
+            layers = self._compositor.layers
+            for widget, (
+                region,
+                _order,
+                _clip,
                 virtual_size,
                 container_size,
-            ) in self._compositor:
-                widget._size_updated(
-                    unclipped_region.size, virtual_size, container_size
-                )
+                _,
+            ) in layers:
+                _size_updated(widget, region.size, virtual_size, container_size)
                 if widget in send_resize:
                     widget.post_message_no_wait(
-                        events.Resize(
-                            self, unclipped_region.size, virtual_size, container_size
-                        )
+                        ResizeEvent(self, region.size, virtual_size, container_size)
                     )
 
         except Exception as error: