Add utility to rr.components.Color to generate colors from any stri…

…ng (and use it in the air traffic data example) (#8458)

### What

It's some time nice to log some color information in multiple entities
to make it easier to relate them visually. This PR adds a
`rr.components.Color.from_str()` utility that does exactly that:
generate a nice color randomly picked up based on the provided string.

This PR also updates the air traffic data example so the barometric
traces have matching colors with the map data.

---------

Co-authored-by: Clement Rey <[email protected]>

examples/python/air_traffic_data/air_traffic_data.py

@@ -239,6 +239,7 @@ def process_measurement(self, measurement: Measurement) -> None:
             )
 
         entity_path = f"aircraft/{measurement.icao_id}"
+        color = rr.components.Color.from_string(entity_path)
 
         if (
             measurement.latitude is not None
@@ -247,13 +248,16 @@ def process_measurement(self, measurement: Measurement) -> None:
         ):
             rr.log(
                 entity_path,
-                rr.Points3D([
-                    self._proj.transform(
-                        measurement.longitude,
-                        measurement.latitude,
-                        measurement.barometric_altitude,
-                    )
-                ]),
+                rr.Points3D(
+                    [
+                        self._proj.transform(
+                            measurement.longitude,
+                            measurement.latitude,
+                            measurement.barometric_altitude,
+                        ),
+                    ],
+                    colors=color,
+                ),
                 rr.GeoPoints(lat_lon=[measurement.latitude, measurement.longitude]),
             )
 
@@ -264,6 +268,7 @@ def process_measurement(self, measurement: Measurement) -> None:
             rr.log(
                 entity_path + "/barometric_altitude",
                 rr.Scalar(measurement.barometric_altitude),
+                rr.SeriesLine(color=color),
             )
 
     def flush(self) -> None:
@@ -310,7 +315,13 @@ def log_position_and_altitude(self, df: polars.DataFrame, icao_id: str) -> None:
             return
 
         if icao_id not in self._position_indicators:
-            rr.log(entity_path, [rr.archetypes.Points3D.indicator(), rr.archetypes.GeoPoints.indicator()], static=True)
+            color = rr.components.Color.from_string(entity_path)
+            rr.log(
+                entity_path,
+                [rr.archetypes.Points3D.indicator(), rr.archetypes.GeoPoints.indicator(), color],
+                static=True,
+            )
+            rr.log(entity_path + "/barometric_altitude", [rr.archetypes.SeriesLine.indicator(), color], static=True)
             self._position_indicators.add(icao_id)
 
         timestamps = rr.TimeSecondsColumn("unix_time", df["timestamp"].to_numpy())

rerun_py/rerun_sdk/rerun/components/color_ext.py

@@ -0,0 +1,28 @@
+from __future__ import annotations
+
+import colorsys
+import math
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from . import Color
+
+_GOLDEN_RATIO = (math.sqrt(5.0) - 1.0) / 2.0
+
+
+class ColorExt:
+    """Extension for [Color][rerun.components.Color]."""
+
+    @staticmethod
+    def from_string(s: str) -> Color:
+        """
+        Generate a random yet deterministic color based on a string.
+
+        The color is guaranteed to be identical for the same input string.
+        """
+
+        from . import Color
+
+        # adapted from egui::PlotUi
+        hue = (hash(s) & 0xFFFF) / 2**16 * _GOLDEN_RATIO
+        return Color([round(comp * 255) for comp in colorsys.hsv_to_rgb(hue, 0.85, 0.5)])