Optimize shouldPausePlacement to short circuit when _forceFullPlaceme…

…nt (maplibre#24)

* shouldPausePlacement short circuits when _forceFullPlacement

* Add generated changelog entries

Co-authored-by: svc-changelog <svc-changelog@palantir.com>

changelog/@unreleased/pr-24.v2.yml

@@ -0,0 +1,11 @@
+type: improvement
+improvement:
+  description: |-
+    Optimize shouldPausePlacement to short circuit when _forceFullPlacement
+
+    Some profiles of Gaia show significant time spent in the following functions. Each iteration of these hot loops makes a call to `shouldPausePlacement`, which previously would need to get the current system time (probably ~50ns), even when `_forceFullPlacement` was true. We now short circuit to avoid the `Date.now()` when `_forceFullPlacement == true`.
+
+        * [continuePlacement](https://github.palantir.build/acme/maplibre-gl-js/blob/8b76c2bc8ff1ec8aa09b83b7f45ca03cb6fcc0e2/src/style/pauseable_placement.ts#L50)
+        * [placeLayerBucketPart](https://github.palantir.build/acme/maplibre-gl-js/blob/8b76c2bc8ff1ec8aa09b83b7f45ca03cb6fcc0e2/src/symbol/placement.ts#L414)
+  links:
+  - https://github.palantir.build/acme/maplibre-gl-js/pull/24

src/style/pauseable_placement.ts

@@ -95,8 +95,10 @@ class PauseablePlacement {
         const startTime = browser.now();
 
         const shouldPausePlacement = () => {
-            const elapsedTime = browser.now() - startTime;
-            return this._forceFullPlacement ? false : elapsedTime > 2;
+            if (this._forceFullPlacement) {
+                return false;
+            }
+            return browser.now() - startTime > 2;
         };
 
         while (this._currentPlacementIndex >= 0) {