improved compositor granularity

tests/test_compositor_regions_to_spans.py

@@ -0,0 +1,48 @@
+from textual._compositor import Compositor
+from textual.geometry import Region
+
+
+def test_regions_to_ranges_no_regions():
+    assert list(Compositor._regions_to_spans([])) == []
+
+
+def test_regions_to_ranges_single_region():
+    regions = [Region(0, 0, 3, 2)]
+    assert list(Compositor._regions_to_spans(regions)) == [(0, 0, 2), (1, 0, 2)]
+
+
+def test_regions_to_ranges_partially_overlapping_regions():
+    regions = [Region(0, 0, 2, 2), Region(1, 1, 2, 2)]
+    assert list(Compositor._regions_to_spans(regions)) == [
+        (0, 0, 1),
+        (1, 0, 2),
+        (2, 1, 2),
+    ]
+
+
+def test_regions_to_ranges_fully_overlapping_regions():
+    regions = [Region(1, 1, 3, 3), Region(2, 2, 1, 1), Region(0, 2, 3, 1)]
+    assert list(Compositor._regions_to_spans(regions)) == [
+        (1, 1, 3),
+        (2, 0, 3),
+        (3, 1, 3),
+    ]
+
+
+def test_regions_to_ranges_disjoint_regions_different_lines():
+    regions = [Region(0, 0, 2, 1), Region(2, 2, 2, 1)]
+    assert list(Compositor._regions_to_spans(regions)) == [(0, 0, 1), (2, 2, 3)]
+
+
+def test_regions_to_ranges_disjoint_regions_same_line():
+    regions = [Region(0, 0, 1, 2), Region(2, 0, 1, 1)]
+    assert list(Compositor._regions_to_spans(regions)) == [
+        (0, 0, 0),
+        (0, 2, 2),
+        (1, 0, 0),
+    ]
+
+
+def test_regions_to_ranges_directly_adjacent_ranges_merged():
+    regions = [Region(0, 0, 1, 2), Region(1, 0, 1, 2)]
+    assert list(Compositor._regions_to_spans(regions)) == [(0, 0, 1), (1, 0, 1)]