Round dashboards: shape and ring, the ring drawn and turned in every look, Knob preset and face guide in the editor

backend/fluksio/flow/dashboards.py

@@ -90,6 +90,12 @@ INPUT_WIDGETS = {
     "color",
 }
 
+#: What a round dashboard may draw on its ring: the widgets that are one value
+#: along a range, which is what turning a knob's ring can set or a circle's
+#: edge can show. Mirrored in the client
+#: (``frontend/src/components/Dashboard/DashboardView.tsx``).
+RING_WIDGETS = {"slider", "dropdown", "color", "gauge"}
+
 #: What a colour widget puts on the wire, by the format it was configured for.
 #: The default is what the Node-RED instance this ports already sends its
 #: DMX encoders — ``[h, s, v]``, hue in degrees and the other two in percent —
@@ -475,6 +481,14 @@ class DashboardDef(BaseModel):
     #: "unset" and the client falls back to its default.
     canvas_width: int = Field(default=1920, ge=0, le=7680)
     canvas_height: int = Field(default=1080, ge=0, le=4320)
+    #: ``round`` draws the dashboard in the circle inscribed in its canvas, for
+    #: a round screen such as a rotary knob. A circle has one size, so a round
+    #: canvas is square: its height is its width.
+    shape: Literal["rect", "round"] = "rect"
+    #: The widget a round dashboard draws along its edge instead of in the grid
+    #: — one of ``RING_WIDGETS``, by id — which a knob's ring turns. Empty
+    #: draws no ring.
+    ring: str = ""
     #: A lucide icon name, drawn on the panel rail; empty falls back to two
     #: letters of the title.
     icon: str = ""
@@ -534,6 +548,24 @@ class DashboardDef(BaseModel):
                 )
         return self
 
+    @model_validator(mode="after")
+    def _check_shape(self) -> DashboardDef:
+        """Square a round canvas, and hold the ring to a widget it can draw."""
+        if self.shape == "round":
+            self.canvas_height = self.canvas_width
+        if not self.ring:
+            return self
+        if self.shape != "round":
+            raise ValueError("only a round dashboard has a ring")
+        widget = next((w for w in self.widgets if w.id == self.ring), None)
+        if widget is None:
+            raise ValueError(
+                f"the ring names '{self.ring}', which is not a widget here"
+            )
+        if widget.type not in RING_WIDGETS:
+            raise ValueError(f"a '{widget.type}' widget cannot be drawn on the ring")
+        return self
+
     @property
     def setting_messages(self) -> list[str]:
         """Every message a bound setting reads. Empty for a static dashboard."""
@@ -549,6 +581,9 @@ class DashboardDef(BaseModel):
         """
         shapes = []
         for widget in self.widgets:
+            # Drawn along the edge, so it takes no place in the grid.
+            if widget.id == self.ring:
+                continue
             at = (
                 widget.layout.get("lg")
                 or widget.layout.get("md")

backend/tests/flow/test_dashboards.py

@@ -445,6 +445,27 @@ def test_a_dashboard_is_cut_into_a_sane_number_of_columns():
             DashboardDef(name="house", columns=columns)
 
 
+def test_a_round_dashboard_is_square_and_rings_one_of_its_own_widgets():
+    dial = WidgetDef(id="dial", type="slider", layout={"lg": Placement(x=1)})
+    stat = WidgetDef(id="stat", type="stat")
+
+    knob = DashboardDef(
+        name="knob",
+        shape="round",
+        canvas_width=360,
+        canvas_height=200,
+        ring="dial",
+        widgets=[dial, stat],
+    )
+
+    assert knob.canvas_height == 360
+    # Drawn along the edge, so the outline of the grid leaves it out.
+    assert [shape.type for shape in knob.footprint] == ["stat"]
+    for shape, ring in (("rect", "dial"), ("round", "gone"), ("round", "stat")):
+        with pytest.raises(ValueError):
+            DashboardDef(name="knob", shape=shape, ring=ring, widgets=[dial, stat])
+
+
 def test_a_setting_refuses_a_message_it_cannot_carry():
     """The same rule a widget binding is held to, from the document alone."""
     DashboardDef(