show hovered point on elevation profile

website/src/lib/engine/engine.test.ts

@@ -259,7 +259,7 @@ describe('statistics', () => {
         assert.equal(get(engine.statistics).hr, undefined);
 
         const request = engine.requestStatistics();
-        await request.set(['hr', 'anchors', 'slopeSegment']);
+        await request.set(['hr', 'anchors', 'slopeSegment', 'segments']);
         const statistics = get(engine.statistics);
         assert.equal(statistics.slopeSegments!.starts[0], 0);
         assert.equal(
@@ -270,6 +270,8 @@ describe('statistics', () => {
         assert.ok(statistics.hr!.some((hr) => !Number.isNaN(hr)));
         assert.equal(statistics.cad, undefined);
         assert.equal(statistics.anchors!.indices[0], 0);
+        assert.deepEqual([...statistics.segments!.starts], [...statistics.anchors!.segmentStarts]);
+        assert.deepEqual(statistics.segments!.ids, statistics.anchors!.segmentIds);
         assert.equal(statistics.anchors!.indices.at(-1), statistics.length - 1);
 
         // they are read again after a change, without being asked again

website/src/lib/engine/statistics.ts

@@ -143,6 +143,14 @@ export class StatisticsReader {
                         };
                         break;
                     }
+                    case 'segments': {
+                        const [starts, ids] = await Promise.all([
+                            backend.segment_starts(),
+                            backend.segment_ids(),
+                        ]);
+                        statistics.segments = { starts, ids };
+                        break;
+                    }
                     case 'highway':
                         [statistics.highway, statistics.sacScale, statistics.mtbScale] =
                             await Promise.all([

website/src/lib/engine/types.ts

@@ -155,7 +155,9 @@ export type StatisticsMetric =
     /** `highway`, `sacScale` and `mtbScale`. */
     | 'highway'
     /** `anchors`. */
-    | 'anchors';
+    | 'anchors'
+    /** `segments`. */
+    | 'segments';
 
 /**
  * The anchors of the routing tool among the trackpoints of the selection: the points that can be
@@ -182,6 +184,15 @@ export type SelectionAnchors = {
     revision: number;
 };
 
+/**
+ * The segments of the selection that have trackpoints: segment `i` has the id `ids[i]`, and its
+ * trackpoints go from `starts[i]` until the next start (or the last trackpoint).
+ */
+export type SelectionSegments = {
+    starts: Uint32Array;
+    ids: string[];
+};
+
 /**
  * The smoothed elevation segments of the selection, over which the slope is averaged, as the
  * intervals of trackpoints that belong to the same one: segment `i` starts at the trackpoint
@@ -229,6 +240,7 @@ export type SelectionStatistics = {
     /** Mountain biking scale. */
     mtbScale?: CategoryIntervals;
     anchors?: SelectionAnchors;
+    segments?: SelectionSegments;
 
     /**
      * Global statistics of the trackpoints from `start` to `end` (both included), for example