fix(waveform): use thin line when downsampling no-line curves

bec_widgets/cli/client.py

@@ -1056,6 +1056,7 @@ class Curve(RPCBase):
         Args:
             pen_style(Literal["solid", "dash", "dot", "dashdot", "none"]): Style of the pen.
                 Use "none" to display markers without connecting lines.
+                During automatic downsampling, "none" uses a 1 px solid line without markers.
         """
 
     @rpc_call

bec_widgets/widgets/plots/waveform/curve.py

@@ -137,17 +137,23 @@ class Curve(BECConnector, pg.PlotDataItem):
             "none": QtCore.Qt.NoPen,
         }
         pen_style = pen_style_map.get(self.config.pen_style, QtCore.Qt.SolidLine)
+        line_fallback = self.config.pen_style == "none" and self.opts["autoDownsample"]
+        pen_width = self.config.pen_width
+        if line_fallback:
+            pen_style = QtCore.Qt.SolidLine
+            pen_width = 1
 
-        pen = pg.mkPen(color=self.config.color, width=self.config.pen_width, style=pen_style)
+        pen = pg.mkPen(color=self.config.color, width=pen_width, style=pen_style)
         self.setPen(pen)
 
-        if self.config.symbol:
+        symbol = None if line_fallback else self.config.symbol
+        if symbol:
             symbol_color = self.config.symbol_color or self.config.color
             brush = pg.mkBrush(color=symbol_color)
 
             self.setSymbolBrush(brush)
             self.setSymbolSize(self.config.symbol_size)
-            self.setSymbol(self.config.symbol)
+        self.setSymbol(symbol)
 
     @property
     def dap_params(self):
@@ -279,8 +285,7 @@ class Curve(BECConnector, pg.PlotDataItem):
             symbol(str): Symbol of the curve.
         """
         self.config.symbol = symbol
-        self.setSymbol(symbol)
-        self.updateItems()
+        self.apply_config()
 
     def set_symbol_color(self, symbol_color: str):
         """
@@ -319,6 +324,7 @@ class Curve(BECConnector, pg.PlotDataItem):
         Args:
             pen_style(Literal["solid", "dash", "dot", "dashdot", "none"]): Style of the pen.
                 Use "none" to display markers without connecting lines.
+                During automatic downsampling, "none" uses a 1 px solid line without markers.
         """
         self.config.pen_style = pen_style
         self.apply_config()

bec_widgets/widgets/plots/waveform/waveform.py

@@ -1938,7 +1938,8 @@ class Waveform(PlotBase):
         Curve items, by deactivating the symbol and activating downsampling auto, method='mean',
         if the data length exceeds N points. If the data length is less than N points, the
         symbol will be activated and downsampling will be deactivated. Maximum points will be
-        5x the limit. Curves without a connecting line retain their markers at any length.
+        5x the limit. The "none" style uses a 1 px solid line without markers while
+        downsampling, retaining its configured appearance for smaller datasets.
 
         Args:
             curve(Curve): The curve to adjust.
@@ -1949,21 +1950,25 @@ class Waveform(PlotBase):
         if limit <= 1:
             logger.warning("Limit must be greater than 1.")
             return
-        if curve.config.pen_style == "none" and curve.config.symbol is None:
-            curve.set_symbol("o")
+        if curve.config.pen_style == "none":
+            downsampling = data_length > limit
+            curve.setDownsampling(ds=None if downsampling else 1, auto=downsampling, method=method)
+            if not downsampling and curve.config.symbol is None:
+                curve.set_symbol("o")
             curve.apply_config()
+            curve.setClipToView(True)
+            return
         if data_length > limit:
-            if curve.config.pen_style != "none" and curve.config.symbol is not None:
+            if curve.config.symbol is not None:
                 curve.set_symbol(None)
             if curve.config.pen_width > 3:
                 curve.set_pen_width(3)
             curve.setDownsampling(ds=None, auto=True, method=method)
             curve.setClipToView(True)
         elif data_length <= limit:
-            if curve.config.pen_style != "none":
-                curve.set_symbol("o")
+            curve.set_symbol("o")
             curve.set_pen_width(4)
-            curve.setDownsampling(ds=1, auto=None, method=method)
+            curve.setDownsampling(ds=1, auto=False, method=method)
             curve.setClipToView(True)
 
     def setup_dap_for_scan(self):

tests/unit_tests/test_waveform.py

@@ -1262,10 +1262,10 @@ def test_curve_no_line_style_preserves_markers(qtbot, mocked_client):
     np.testing.assert_array_equal(curve.scatter.getData(), [[2, 3, 4], [5, 6, 7]])
 
 
-@pytest.mark.parametrize("data_length", [500, 1500])
+@pytest.mark.parametrize("data_length", [1000, 1001])
 @pytest.mark.parametrize("symbol", [None, "d"])
-def test_curve_no_line_style_keeps_async_markers(qtbot, mocked_client, data_length, symbol):
-    """Async data retain markers, including when automatic styling previously hid them."""
+def test_curve_no_line_style_async_downsampling(qtbot, mocked_client, data_length, symbol):
+    """No-line curves fall back to a thin line without markers above the async limit."""
     wf = create_widget(qtbot, Waveform, client=mocked_client)
     curve = wf.plot(
         x=[1, 2, 3],
@@ -1280,6 +1280,13 @@ def test_curve_no_line_style_keeps_async_markers(qtbot, mocked_client, data_leng
     wf._auto_adjust_async_curve_settings(curve, data_length)
     curve.setData(np.arange(data_length), np.arange(data_length))
 
+    assert curve.config.pen_style == "none"
+    assert curve.config.pen_width == 3
+    if data_length > 1000:
+        assert curve.curve.opts["pen"].style() == Qt.SolidLine
+        assert curve.curve.opts["pen"].widthF() == 1
+        assert not curve.scatter.isVisible()
+        return
     assert curve.curve.opts["pen"].style() == Qt.NoPen
     assert curve.scatter.isVisible()
     assert curve.config.symbol == (symbol or "o")
@@ -1288,6 +1295,54 @@ def test_curve_no_line_style_keeps_async_markers(qtbot, mocked_client, data_leng
     assert curve.scatter.opts["brush"].color().name() == "#654321"
 
 
+def test_curve_no_line_downsampling_style_updates_and_restore(qtbot, mocked_client):
+    """Appearance updates keep the fallback, and smaller data restore the saved markers."""
+    wf = create_widget(qtbot, Waveform, client=mocked_client)
+    curve = wf.plot(x=np.arange(1500), y=np.arange(1500))
+    wf._auto_adjust_async_curve_settings(curve, 1500)
+    curve.set_pen_style("none")
+    assert curve.curve.opts["pen"].style() == Qt.SolidLine
+    assert curve.curve.opts["pen"].widthF() == 1
+    assert not curve.scatter.isVisible()
+
+    curve.set_color("#123456")
+    curve.set_pen_width(7)
+    curve.set_symbol("d")
+    curve.set_symbol_color("#654321")
+    curve.set_symbol_size(12)
+    assert curve.curve.opts["pen"].style() == Qt.SolidLine
+    assert curve.curve.opts["pen"].widthF() == 1
+    assert curve.curve.opts["pen"].color().name() == "#123456"
+    assert not curve.scatter.isVisible()
+    assert curve.config.pen_style == "none"
+    assert curve.config.pen_width == 7
+    assert curve.config.symbol == "d"
+
+    wf._auto_adjust_async_curve_settings(curve, 1000)
+    curve.setData(np.arange(1000), np.arange(1000))
+    assert not curve.opts["autoDownsample"]
+    assert curve.curve.opts["pen"].style() == Qt.NoPen
+    assert curve.config.pen_width == 7
+    assert curve.scatter.isVisible()
+    assert curve.scatter.opts["symbol"] == "d"
+    assert curve.scatter.opts["size"] == 12
+    assert curve.scatter.opts["brush"].color().name() == "#654321"
+
+
+def test_curve_no_line_after_named_style_downsampling_ends(qtbot, mocked_client):
+    """Selecting no line after a named style leaves downsampling does not keep the fallback."""
+    wf = create_widget(qtbot, Waveform, client=mocked_client)
+    curve = wf.plot(x=np.arange(1500), y=np.arange(1500))
+    wf._auto_adjust_async_curve_settings(curve, 1500)
+    wf._auto_adjust_async_curve_settings(curve, 1000)
+    curve.setData(np.arange(1000), np.arange(1000))
+    curve.set_pen_style("none")
+
+    assert not curve.opts["autoDownsample"]
+    assert curve.curve.opts["pen"].style() == Qt.NoPen
+    assert curve.scatter.isVisible()
+
+
 def test_curve_no_line_style_restores_existing_styles(qtbot, mocked_client):
     """The no-line style is reversible, and legacy null styles still draw solid lines."""
     wf = create_widget(qtbot, Waveform, client=mocked_client)