step 3: add widget shell sizing and frame pump

tests/test_sizing.py

@@ -0,0 +1,44 @@
+from __future__ import annotations
+
+from dpg_map.sizing import SizeMeasurement, apply_size_measurement, effective_draw_size
+from dpg_map.state import DirtyFlags, create_map_state
+
+
+def test_size_measurement_tracks_last_nonzero_size() -> None:
+    state = create_map_state(tag="size-last-nonzero")
+
+    first = apply_size_measurement(state, SizeMeasurement(width=640, height=360, visible=True))
+    hidden = apply_size_measurement(state, SizeMeasurement(width=0, height=0, visible=False))
+
+    assert first.changed is True
+    assert state.measured_width == 0
+    assert state.measured_height == 0
+    assert state.last_nonzero_width == 640
+    assert state.last_nonzero_height == 360
+    assert hidden.became_hidden is True
+    assert effective_draw_size(state) == (640, 360)
+
+
+def test_zero_size_does_not_permanently_collapse_map() -> None:
+    state = create_map_state(tag="size-reappears")
+
+    apply_size_measurement(state, SizeMeasurement(width=500, height=300, visible=True))
+    apply_size_measurement(state, SizeMeasurement(width=0, height=0, visible=False))
+    update = apply_size_measurement(state, SizeMeasurement(width=700, height=450, visible=True))
+
+    assert update.became_visible is True
+    assert update.effective_width == 700
+    assert update.effective_height == 450
+    assert state.last_nonzero_width == 700
+    assert state.last_nonzero_height == 450
+
+
+def test_resize_marks_size_dirty() -> None:
+    state = create_map_state(tag="size-dirty")
+    state.dirty = DirtyFlags.NONE
+
+    apply_size_measurement(state, SizeMeasurement(width=320, height=240, visible=True))
+
+    assert state.dirty & DirtyFlags.SIZE
+    assert state.dirty & DirtyFlags.TILES
+    assert state.dirty & DirtyFlags.OVERLAYS