Feature: first version of clustering at low zoom levels, filters don't update yet (WIP)

src/Logic/FeatureSource/Sources/IfVisibleFeatureSource.ts

@@ -0,0 +1,38 @@
+import { FeatureSource } from "../FeatureSource"
+import { Feature } from "geojson"
+import { Store, UIEventSource } from "../../UIEventSource"
+
+export class IfVisibleFeatureSource<T extends Feature> implements FeatureSource<T> {
+
+    private readonly _features: UIEventSource<T[]> = new UIEventSource<T[]>([])
+    public readonly features: Store<T[]> = this._features
+
+    constructor(upstream: FeatureSource<T>, visible: Store<boolean>) {
+
+        let dirty = false
+        upstream.features.addCallbackAndRun(features => {
+            if (!visible.data) {
+                console.log(">>> not writing data as not visible")
+                dirty = true
+                return
+            }
+            this._features.set(features)
+            dirty = false
+        })
+
+        visible.addCallbackAndRun(isVisible => {
+            if (isVisible && dirty) {
+                this._features.set(upstream.features.data)
+                dirty = false
+            }
+            if (!visible) {
+                this._features.set([])
+            }
+
+        })
+
+
+    }
+
+
+}