optimized line_crop

src/textual/_compositor.py

@@ -28,6 +28,7 @@ from .geometry import Region, Offset, Size
 
 
 from ._loop import loop_last
+from ._segment_tools import line_crop
 from ._types import Lines
 from .widget import Widget
 
@@ -412,7 +413,6 @@ class Compositor:
         else:
             widget_regions = []
 
-        divide = Segment.divide
         intersection = Region.intersection
         overlaps = Region.overlaps
 
@@ -425,9 +425,9 @@ class Compositor:
                 new_x, new_y, new_width, new_height = intersection(region, clip)
                 delta_x = new_x - region.x
                 delta_y = new_y - region.y
-                splits = [delta_x, delta_x + new_width]
+                crop_x = delta_x + new_width
                 lines = widget.get_render_lines(delta_y, delta_y + new_height)
-                lines = [list(divide(line, splits))[1] for line in lines]
+                lines = [line_crop(line, delta_x, crop_x) for line in lines]
                 yield region, clip, lines
 
     @classmethod
@@ -509,13 +509,11 @@ class Compositor:
         crop_x, crop_y, crop_x2, crop_y2 = crop_region.corners
         render_lines = self._assemble_chops(chops[crop_y:crop_y2])
 
-        def width_view(line: list[Segment]) -> list[Segment]:
-            div_lines = list(divide(line, [crop_x, crop_x2]))
-            line = div_lines[1] if len(div_lines) > 1 else div_lines[0]
-            return line
-
         if crop is not None and (crop_x, crop_x2) != (0, width):
-            render_lines = [width_view(line) if line else line for line in render_lines]
+            render_lines = [
+                line_crop(line, crop_x, crop_x2) if line else line
+                for line in render_lines
+            ]
 
         return SegmentLines(render_lines, new_lines=True)
 

src/textual/_lines.py

@@ -1,17 +0,0 @@
-from __future__ import annotations
-
-from rich.segment import Segment
-
-from .geometry import Region
-from ._types import Lines
-
-
-def crop_lines(lines: Lines, clip: Region) -> Lines:
-    lines = lines[clip.y : clip.y + clip.height]
-
-    def width_view(line: list[Segment]) -> list[Segment]:
-        _, line = Segment.divide(line, [clip.x, clip.x + clip.width])
-        return line
-
-    cropped_lines = [width_view(line) for line in lines]
-    return cropped_lines

src/textual/_segment_tools.py

@@ -0,0 +1,49 @@
+"""
+Tools for processing Segments, or lists of Segments.
+"""
+
+from __future__ import annotations
+
+from rich.segment import Segment
+
+
+def line_crop(segments: list[Segment], start: int, end: int) -> list[Segment]:
+    """Crops a list of segments between two cell offsets.
+
+    Args:
+        segments (list[Segment]): A list of Segments for a line.
+        start (int): Start offset
+        end (int): End offset
+
+    Returns:
+        list[Segment]: A new shorter list of segments
+    """
+    # This is essentially a specialized version of Segment.divide
+    # The following line has equivalent functionality (but a little slower)
+    # return list(Segment.divide(segments, [start, end]))[1]
+    pos = 0
+    output_segments: list[Segment] = []
+    add_segment = output_segments.append
+    iter_segments = iter(segments)
+    segment: Segment | None = None
+    for segment in iter_segments:
+        end_pos = pos + segment.cell_length
+        if end_pos > start:
+            segment = segment.split_cells(start - pos)[-1]
+            break
+        pos = end_pos
+    else:
+        return []
+
+    pos = start
+    while segment is not None:
+        end_pos = pos + segment.cell_length
+        if end_pos < end:
+            add_segment(segment)
+        else:
+            add_segment(segment.split_cells(end - pos)[0])
+            break
+        pos = end_pos
+        segment = next(iter_segments, None)
+
+    return output_segments

tests/test_segment_tools.py

@@ -0,0 +1,55 @@
+from rich.segment import Segment
+from rich.style import Style
+
+
+from textual._segment_tools import line_crop
+
+
+def test_line_crop():
+    bold = Style(bold=True)
+    italic = Style(italic=True)
+    segments = [
+        Segment("Hello", bold),
+        Segment(" World!", italic),
+    ]
+
+    assert line_crop(segments, 1, 2) == [Segment("e", bold)]
+    assert line_crop(segments, 4, 20) == [
+        Segment("o", bold),
+        Segment(" World!", italic),
+    ]
+
+
+def test_line_crop_emoji():
+    bold = Style(bold=True)
+    italic = Style(italic=True)
+    segments = [
+        Segment("Hello", bold),
+        Segment("💩💩💩", italic),
+    ]
+    assert line_crop(segments, 8, 11) == [Segment(" 💩", italic)]
+    assert line_crop(segments, 9, 11) == [Segment("💩", italic)]
+
+
+def test_line_crop_edge():
+    segments = [Segment("foo"), Segment("bar"), Segment("baz")]
+    assert line_crop(segments, 2, 9) == [Segment("o"), Segment("bar"), Segment("baz")]
+    assert line_crop(segments, 3, 9) == [Segment("bar"), Segment("baz")]
+    assert line_crop(segments, 4, 9) == [Segment("ar"), Segment("baz")]
+    assert line_crop(segments, 4, 8) == [Segment("ar"), Segment("ba")]
+
+
+def test_line_crop_edge_2():
+    segments = [
+        Segment("╭─"),
+        Segment(
+            "────── Placeholder ───────",
+        ),
+        Segment(
+            "─╮",
+        ),
+    ]
+    result = line_crop(segments, 30, 60)
+    expected = []
+    print(repr(result))
+    assert result == expected