Prevent nodes out of viewport triggering render (#296)

* Prevent nodes out of viewport triggering render

* Update frontend/src/common/SortedCollection.ts

Co-authored-by: David <dvdplm@gmail.com>

* Tweak the comment on `setFocus`, move it closer to `ref` and `hasChangedSince`

* Switch `SortedCollection.ref()` to a getter

Co-authored-by: David <dvdplm@gmail.com>

frontend/src/Connection.ts

@@ -149,7 +149,7 @@ export class Connection {
 
   public handleMessages = (messages: FeedMessage.Message[]) => {
     const { nodes, chains, sortBy, selectedColumns } = this.state;
-    const ref = nodes.ref();
+    const { ref } = nodes;
 
     const updateState: UpdateBound = (state) => {
       this.state = this.update(state);

frontend/src/common/SortedCollection.ts

@@ -97,11 +97,27 @@ export namespace SortedCollection {
   export type StateRef = Opaque<number, 'SortedCollection.StateRef'>;
 }
 
+interface Focus {
+  start: number;
+  end: number;
+}
+
 export class SortedCollection<Item extends { id: number }> {
+  // Comparator function used to sort the collection
   private compare: Compare<Item>;
+  // Mapping item `id` to the `Item`, this uses array as a structure with
+  // the assumption that `id`s provided are increments from `0`, and that
+  // vacant `id`s will be re-used in the future.
   private map = Array<Maybe<Item>>();
+  // Actual sorted list of `Item`s.
   private list = Array<Item>();
+  // Internal tracker for changes, this number increments whenever the
+  // order of the **focused** elements in the collection changes
   private changeRef = 0;
+  // Marks the range of indicies that are focused for tracking.
+  // **Note:** `start` is inclusive, while `end` is exclusive (much like
+  // `Array.slice()`).
+  private focus: Focus = { start: 0, end: 0 };
 
   constructor(compare: Compare<Item>) {
     this.compare = compare;
@@ -114,10 +130,6 @@ export class SortedCollection<Item extends { id: number }> {
     this.changeRef += 1;
   }
 
-  public ref(): SortedCollection.StateRef {
-    return this.changeRef as SortedCollection.StateRef;
-  }
-
   public add(item: Item) {
     if (this.map.length <= item.id) {
       // Grow map if item.id would be out of scope
@@ -131,9 +143,11 @@ export class SortedCollection<Item extends { id: number }> {
 
     this.map[item.id] = item;
 
-    sortedInsert(item, this.list, this.compare);
+    const index = sortedInsert(item, this.list, this.compare);
 
-    this.changeRef += 1;
+    if (index < this.focus.end) {
+      this.changeRef += 1;
+    }
   }
 
   public remove(id: number) {
@@ -147,7 +161,9 @@ export class SortedCollection<Item extends { id: number }> {
     this.list.splice(index, 1);
     this.map[id] = null;
 
-    this.changeRef += 1;
+    if (index < this.focus.end) {
+      this.changeRef += 1;
+    }
   }
 
   public get(id: number): Maybe<Item> {
@@ -184,7 +200,13 @@ export class SortedCollection<Item extends { id: number }> {
     const newIndex = sortedInsert(item, this.list, this.compare);
 
     if (newIndex !== index) {
-      this.changeRef += 1;
+      const outOfFocus =
+        (index < this.focus.start && newIndex < this.focus.start) ||
+        (index >= this.focus.end && newIndex >= this.focus.end);
+
+      if (!outOfFocus) {
+        this.changeRef += 1;
+      }
     }
   }
 
@@ -207,6 +229,7 @@ export class SortedCollection<Item extends { id: number }> {
   public mutEachAndSort(mutator: (item: Item) => void) {
     this.list.forEach(mutator);
     this.list.sort(this.compare);
+    this.changeRef += 1;
   }
 
   public clear() {
@@ -216,6 +239,18 @@ export class SortedCollection<Item extends { id: number }> {
     this.changeRef += 1;
   }
 
+  // Set a new `Focus`. Any changes to the order of items within the `Focus`
+  // will increment `changeRef`.
+  public setFocus(start: number, end: number) {
+    this.focus = { start, end };
+  }
+
+  // Get the reference to current ordering state of focused items.
+  public get ref(): SortedCollection.StateRef {
+    return this.changeRef as SortedCollection.StateRef;
+  }
+
+  // Check if order of focused items has changed since obtaining a `ref`.
   public hasChangedSince(ref: SortedCollection.StateRef): boolean {
     return this.changeRef > ref;
   }

frontend/src/components/List/List.tsx

@@ -52,11 +52,11 @@ export class List extends React.Component<List.Props, {}> {
   }
 
   public render() {
-    const { selectedColumns } = this.props.appState;
-    const { pins, sortBy } = this.props;
-    const { filter } = this.state;
+    const { pins, sortBy, appState } = this.props;
+    const { selectedColumns } = appState;
+    const { filter, listStart, listEnd } = this.state;
 
-    let nodes = this.props.appState.nodes.sorted();
+    let nodes = appState.nodes.sorted();
 
     if (filter != null) {
       nodes = nodes.filter(filter);
@@ -73,10 +73,13 @@ export class List extends React.Component<List.Props, {}> {
           </React.Fragment>
         );
       }
+      // With filter present, we can no longer guarantee that focus corresponds
+      // to rendering view, so we put the whole list in focus
+      appState.nodes.setFocus(0, nodes.length);
+    } else {
+      appState.nodes.setFocus(listStart, listEnd);
     }
 
-    const { listStart, listEnd } = this.state;
-
     const height = TH_HEIGHT + nodes.length * TR_HEIGHT;
     const transform = `translateY(${listStart * TR_HEIGHT}px)`;