fix(scatter_waveform): trim live x/y/z buffers to common length before plotting

bec_widgets/widgets/plots/scatter_waveform/scatter_waveform.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import numpy as np
 import pyqtgraph as pg
 from bec_lib import bec_logger
 from bec_lib.endpoints import MessageEndpoints
@@ -369,7 +370,14 @@ class ScatterWaveform(PlotBase):
             y_data = data.get(device_y, {}).get(signal_y, {}).read().get("value", None)
             z_data = data.get(device_z, {}).get(signal_z, {}).read().get("value", None)
 
-        self._main_curve.set_data(x=x_data, y=y_data, z=z_data)
+        if x_data is None or y_data is None or z_data is None:
+            return
+
+        x_data, y_data, z_data = (np.atleast_1d(arr) for arr in (x_data, y_data, z_data))
+        min_len = min(len(x_data), len(y_data), len(z_data))
+        if min_len == 0:
+            return
+        self._main_curve.set_data(x=x_data[:min_len], y=y_data[:min_len], z=z_data[:min_len])
 
     def _fetch_scan_data_and_access(self):
         """

tests/unit_tests/test_scatter_waveform.py

@@ -10,7 +10,7 @@ from bec_widgets.widgets.plots.scatter_waveform.scatter_waveform import ScatterW
 from bec_widgets.widgets.plots.scatter_waveform.settings.scatter_curve_setting import (
     ScatterCurveSettings,
 )
-from tests.unit_tests.client_mocks import create_dummy_scan_item, mocked_client
+from tests.unit_tests.client_mocks import DummyData, create_dummy_scan_item, mocked_client
 
 from .conftest import create_widget
 
@@ -574,6 +574,69 @@ def test_z_gradient_uses_shared_brush_pool(qtbot, mocked_client):
     assert brushes_first[-1].color().getRgb()[:3] == hi.getRgb()[:3]
 
 
+def test_scatter_waveform_live_update_unequal_lengths(qtbot, mocked_client, monkeypatch):
+    """Device buffers fill independently during a live scan, so one of them can
+    be a point ahead when the update slot fires; the data must be trimmed to the
+    common length instead of handing pyqtgraph mismatched arrays."""
+    swf = create_widget(qtbot, ScatterWaveform, client=mocked_client)
+
+    dummy_scan = create_dummy_scan_item()
+    # samx is one point ahead of samy and bpm4i
+    dummy_scan.live_data["samx"]["samx"].val = [10, 20, 30, 40]
+    monkeypatch.setattr(swf.queue.scan_storage, "find_scan_by_ID", lambda scan_id: dummy_scan)
+
+    swf.plot("samx", "samy", "bpm4i", label="live_curve")
+    swf.scan_id = "dummy"
+    swf.scan_item = dummy_scan
+
+    swf.update_sync_curves()
+
+    x_data, y_data = swf.main_curve.getData()
+    np.testing.assert_array_equal(x_data, [10, 20, 30])
+    np.testing.assert_array_equal(y_data, [5, 10, 15])
+
+
+def test_scatter_waveform_live_update_incomplete_data(qtbot, mocked_client, monkeypatch):
+    """Missing or empty device buffers skip the update instead of erroring."""
+    swf = create_widget(qtbot, ScatterWaveform, client=mocked_client)
+
+    dummy_scan = create_dummy_scan_item()
+    dummy_scan.live_data["samy"] = {}  # y signal not delivered yet
+    monkeypatch.setattr(swf.queue.scan_storage, "find_scan_by_ID", lambda scan_id: dummy_scan)
+
+    swf.plot("samx", "samy", "bpm4i", label="live_curve")
+    swf.scan_id = "dummy"
+    swf.scan_item = dummy_scan
+
+    swf.update_sync_curves()
+    assert swf.main_curve.getData() == (None, None)
+
+    dummy_scan.live_data["samy"] = {"samy": DummyData(val=[], timestamps=[])}
+    swf.update_sync_curves()
+    assert swf.main_curve.getData() == (None, None)
+
+
+def test_scatter_waveform_live_update_scalar_readback(qtbot, mocked_client, monkeypatch):
+    """The first live update can deliver bare scalar readbacks instead of buffers;
+    they must be plotted as a single point, not raise TypeError on len()."""
+    swf = create_widget(qtbot, ScatterWaveform, client=mocked_client)
+
+    dummy_scan = create_dummy_scan_item()
+    for device in ("samx", "samy", "bpm4i"):
+        dummy_scan.live_data[device][device] = DummyData(val=5.0, timestamps=100)
+    monkeypatch.setattr(swf.queue.scan_storage, "find_scan_by_ID", lambda scan_id: dummy_scan)
+
+    swf.plot("samx", "samy", "bpm4i", label="live_curve")
+    swf.scan_id = "dummy"
+    swf.scan_item = dummy_scan
+
+    swf.update_sync_curves()
+
+    x_data, y_data = swf.main_curve.getData()
+    np.testing.assert_array_equal(x_data, [5.0])
+    np.testing.assert_array_equal(y_data, [5.0])
+
+
 def test_z_gradient_flat_and_empty_z(qtbot, mocked_client):
     """Degenerate z inputs keep returning None (no gradient)."""
     swf = create_widget(qtbot, ScatterWaveform, client=mocked_client)