feat: use ECharts to have faster charts (and more interactive)

documentation/changelog.rst

@@ -12,7 +12,7 @@ v1.0.0 | July XX, 2026
 
 New features
 -------------
-
+* In the UI, an opt-in "Fast chart" mode renders asset and sensor charts with Apache ECharts (canvas) for much faster drawing and interaction on dense time series, while staying visually and functionally equivalent to the existing Vega-Lite charts [see `PR #2234 <https://www.github.com/FlexMeasures/flexmeasures/pull/2234>`_]
 * Breaking behaviour change: the top-level flex-context's ``relax-constraints`` field now defaults to ``True`` (matching the default already used within each ``commodities`` entry), so constraint violations are softly penalized by default instead of being hard constraints, unless explicitly set to ``False`` [see `PR #2172 <https://www.github.com/FlexMeasures/flexmeasures/pull/2172>`_]
 * Support for creating new assets by using another asset as a template from the UI. [see `PR #2195 <https://www.github.com/FlexMeasures/flexmeasures/pull/2195>`_ and `PR #2268 <https://www.github.com/FlexMeasures/flexmeasures/pull/2268>`_
 * In the UI, asset and sensor lists can be filtered by ID prefix through API-backed search fields [see `PR #2231 <https://www.github.com/FlexMeasures/flexmeasures/pull/2231>`_]

flexmeasures/data/models/generic_assets.py

@@ -641,6 +641,7 @@ def _create_fixed_value_sensors(
                 id=fixed_value_sensor.id,
                 name=sensor_name,
                 sensor_unit=ref["unit"],
+                event_resolution=fixed_value_sensor.event_resolution.total_seconds(),
                 description=sensor_name,
                 asset_id=parent_asset.id,
                 asset_description=parent_asset.name,
@@ -1084,6 +1085,12 @@ def chart_data_json(
                     sensors_meta[str(sensor.id)] = {
                         "name": as_dict.get("name", sensor.name),
                         "unit": as_dict.get("sensor_unit", sensor.unit),
+                        # Fixed-value sensors are instantaneous (0), so the chart
+                        # renders their row with linear interpolation like Vega-Lite.
+                        "event_resolution": as_dict.get(
+                            "event_resolution",
+                            sensor.event_resolution.total_seconds(),
+                        ),
                         "description": as_dict.get("description", sensor.name),
                         "asset_id": as_dict.get("asset_id"),
                         "asset_description": as_dict.get("asset_description", ""),
@@ -1291,6 +1298,9 @@ def search_beliefs(  # noqa C901
                     sensors_metadata[sensor.id] = {
                         "name": sensor_dict.get("name", ""),
                         "unit": sensor_dict.get("unit", sensor.unit),
+                        "event_resolution": sensor_dict.get(
+                            "event_resolution", sensor.event_resolution.total_seconds()
+                        ),
                         "description": sensor_dict.get("description", ""),
                         "asset_id": sensor_dict.get(
                             "asset_id", getattr(sensor, "generic_asset_id", None)

flexmeasures/data/models/time_series.py

@@ -474,6 +474,9 @@ def search_beliefs(  # noqa: C901
             sensors_metadata[self.id] = {
                 "name": sensor_dict.get("name", ""),
                 "unit": sensor_dict.get("sensor_unit", self.unit),
+                "event_resolution": sensor_dict.get(
+                    "event_resolution", self.event_resolution.total_seconds()
+                ),
                 "description": sensor_dict.get("description", ""),
                 "asset_id": sensor_dict.get(
                     "asset_id", getattr(self, "generic_asset_id", None)
@@ -703,6 +706,7 @@ def as_dict(self) -> dict:
             id=self.id,
             name=self.name,
             sensor_unit=self.unit,
+            event_resolution=self.event_resolution.total_seconds(),
             description=f"{self.name} ({self.generic_asset.name})",
             asset_description=f"{self.generic_asset.name}"
             + (f" ({parent_asset.name})" if parent_asset is not None else ""),

flexmeasures/ui/__init__.py

@@ -162,6 +162,23 @@ def basic_admin_auth():
 
 def add_jinja_filters(app):
     from flexmeasures.ui.utils.view_utils import asset_icon_name, username, accountname
+    from flexmeasures.data.models.charts.belief_charts import (
+        determine_shared_sensor_type,
+    )
+
+    def shared_sensor_type(sensors):
+        """Mirror the Vega-Lite y-axis title logic: if all sensors share a
+        sensor type use it, otherwise derive the dimension from the shared unit
+        (e.g. a group of kW sensors becomes "power").
+
+        ``sensor_type`` is normally set lazily inside the chart methods, so we
+        populate it here (as ``get_attribute("sensor_type", name)``) before
+        delegating to the shared helper.
+        """
+        sensors = list(sensors)
+        for sensor in sensors:
+            sensor.sensor_type = sensor.get_attribute("sensor_type", sensor.name)
+        return determine_shared_sensor_type(sensors)
 
     app.jinja_env.filters["zip"] = zip  # Allow zip function in templates
     app.jinja_env.add_extension(
@@ -174,6 +191,7 @@ def add_jinja_filters(app):
     app.jinja_env.filters["capitalize"] = capitalize
     app.jinja_env.filters["pluralize"] = pluralize
     app.jinja_env.filters["parameterize"] = parameterize
+    app.jinja_env.filters["shared_sensor_type"] = shared_sensor_type
     app.jinja_env.filters["isnull"] = pd.isnull
     app.jinja_env.filters["hide_nan_if_desired"] = lambda x: (
         ""

flexmeasures/ui/static/js/chart-data-utils.js

@@ -46,6 +46,7 @@ export function decompressChartData(responseData) {
           name: sensor.name || "",
           sensor_unit: sensor.unit || "",
           unit: sensor.unit || "",
+          event_resolution: sensor.event_resolution,
           description: sensor.description || "",
           asset_id: sensor.asset_id,
           asset_description: sensor.asset_description || "",