From 784293d713082967af1e274874ead743ee549ceb Mon Sep 17 00:00:00 2001
From: Vladimir Agafonkin <agafonkin@gmail.com>
Date: Thu, 16 Aug 2018 13:08:14 -0700
Subject: [PATCH] fix buffer offset for feature state, more resilient structure

---
 src/data/feature_position_map.js  | 16 ++++++++++------
 src/data/program_configuration.js |  5 ++++-
 2 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/src/data/feature_position_map.js b/src/data/feature_position_map.js
index bd83d69cef9..a8c5c9bb586 100644
--- a/src/data/feature_position_map.js
+++ b/src/data/feature_position_map.js
@@ -1,6 +1,7 @@
 // @flow
 
 import { register } from '../util/web_worker_transfer';
+import assert from 'assert';
 
 type SerializedFeaturePositionMap = {
     ids: Float64Array;
@@ -17,22 +18,24 @@ type FeaturePosition = {
 export default class FeaturePositionMap {
     ids: Array<number>;
     positions: Array<number>;
-    _bufferLen: number;
+    indexed: boolean;
 
     constructor() {
         this.ids = [];
         this.positions = [];
-        this._bufferLen = 0;
+        this.indexed = false;
     }
 
-    add(id: number, index: number, newLength: number) {
+    add(id: number, index: number, start: number, end: number) {
         this.ids.push(id);
-        this.positions.push(index, this._bufferLen, newLength);
-        this._bufferLen = newLength;
+        this.positions.push(index, start, end);
     }
 
     getPositions(id: number): Array<FeaturePosition> {
-        // binary search for the first occurrence of id in this.ids
+        assert(this.indexed);
+
+        // binary search for the first occurrence of id in this.ids;
+        // relies on ids/positions being sorted by id, which happens in serialization
         let i = 0;
         let j = this.ids.length - 1;
         while (i < j) {
@@ -71,6 +74,7 @@ export default class FeaturePositionMap {
         // so TypedArray vs Array distinction that flow points out doesn't matter
         map.ids = (obj.ids: any);
         map.positions = (obj.positions: any);
+        map.indexed = true;
         return map;
     }
 }
diff --git a/src/data/program_configuration.js b/src/data/program_configuration.js
index 3f4c4e84ff7..997aab5784b 100644
--- a/src/data/program_configuration.js
+++ b/src/data/program_configuration.js
@@ -360,6 +360,7 @@ export default class ProgramConfiguration {
 
     _buffers: Array<VertexBuffer>;
     _featureMap: FeaturePositionMap;
+    _bufferOffset: number;
 
     constructor() {
         this.binders = {};
@@ -367,6 +368,7 @@ export default class ProgramConfiguration {
 
         this._buffers = [];
         this._featureMap = new FeaturePositionMap();
+        this._bufferOffset = 0;
     }
 
     static createDynamic<Layer: TypedStyleLayer>(layer: Layer, zoom: number, filterProperties: (string) => boolean) {
@@ -405,8 +407,9 @@ export default class ProgramConfiguration {
             this.binders[property].populatePaintArray(newLength, feature);
         }
         if (feature.id !== undefined) {
-            this._featureMap.add(+feature.id, index, newLength);
+            this._featureMap.add(+feature.id, index, this._bufferOffset, newLength);
         }
+        this._bufferOffset = newLength;
     }
 
     updatePaintArrays(featureStates: FeatureStates, vtLayer: VectorTileLayer, layer: TypedStyleLayer): boolean {