step 6: add stable overlays and live update stress tests

tests/test_overlays_state.py

@@ -1,8 +1,11 @@
 from __future__ import annotations
 
+from threading import Thread
+
 import pytest
 
 import dpg_map as dpgm
+from dpg_map.commands import CommandKind
 from dpg_map.exceptions import CoordinateError
 from dpg_map.overlays import TrajectoryOverlay
 from dpg_map.state import DirtyFlags, create_map_state, get_map_state
@@ -61,3 +64,39 @@ def test_layer_state_tracks_visibility_and_overlay_membership() -> None:
 
     assert state.layers["fleet"].overlay_tags == set()
     assert "vehicle" not in state.overlays
+
+
+def test_threaded_marker_updates_coalesce_without_touching_view_or_drag_state() -> None:
+    create_map_state(tag="threaded-marker", center=(47.0, 2.0), zoom=9)
+    dpgm.add_marker("vehicle", lat=47.0, lon=2.0, map_tag="threaded-marker")
+    state = get_map_state("threaded-marker")
+    state.command_queue.drain()
+    state.dirty = DirtyFlags.NONE
+    state.interaction.active_drag = True
+    state.interaction.last_mouse_position = (100.0, 100.0)
+    before_center = state.center
+    before_zoom = state.zoom
+
+    def update_worker(offset: float) -> None:
+        for index in range(100):
+            dpgm.update_marker(
+                "vehicle",
+                lat=47.0 + offset,
+                lon=2.0 + index * 0.00001,
+                map_tag="threaded-marker",
+            )
+
+    threads = [Thread(target=update_worker, args=(worker * 0.0001,)) for worker in range(4)]
+    for thread in threads:
+        thread.start()
+    for thread in threads:
+        thread.join()
+
+    commands = state.command_queue.drain()
+
+    assert state.center == before_center
+    assert state.zoom == before_zoom
+    assert state.interaction.active_drag is True
+    assert state.interaction.last_mouse_position == (100.0, 100.0)
+    assert state.dirty == DirtyFlags.OVERLAYS
+    assert [command.kind for command in commands] == [CommandKind.UPDATE_OVERLAY]