[tordans]

Disclaimer: Found and fixed with Clause Opus 5.5 High. Description also written by Claude and reviewed by me.

The problem

<Layer> and <Source> subscribe to the map's styledata event and force a render on every event. MapLibre and Mapbox fire styledata for every style change: map.addImage, map.setPaintProperty, a layer that another component adds. So with 120 <Layer>s, every icon an app loads at runtime renders all 120 again, and every <Source> schedules a timer and a render.

Those renders find the layer or source in the style and call updateLayer / updateSource with unchanged props, which does nothing. The render only does useful work when the layer or source is missing from a loaded style, for example after a style swap.

The change

The styledata listener now forces a render only when the layer (map.getLayer(id)) or source (map.getSource(id)) is missing, or the style is not loaded. The subscription and the map.style._loaded check stay as they are, so the timing of when sources and layers are added is unchanged (see the reverts in #2526).

Applied to layer.ts and source.ts in react-maplibre and react-mapbox. I left the mapbox-legacy copy in modules/main alone.

Unchanged behaviour:

• After a style swap, layers and sources are missing, so they are added again (covered by the existing Source/Layer tests).
• A layer whose source or beforeId is not in the style yet is still missing, so it renders again on the next styledata and is added then.
• While the style is not loaded, every event still renders.

New test in both packages: addImage + setPaintProperty no longer render <Source> or <Layer>, and a layer removed outside React is added again. It fails without the change.

Measured, before and after

120 layers on 4 GeoJSON sources (10,000 features). Each <Layer> and <Source> is wrapped in its own React.Profiler. Chrome 153 headless, Apple M4, maplibre-gl 6.14.0, React 18.3.1, median of 5 page loads per build.

Scenario		before	after
50 × addImage, one per frame (100 styledata)	<Layer> renders	6,120	0
	<Source> renders	208	0
	React render time	5.6 ms	0 ms
	main-thread script time	82.1 ms	68.0 ms
50 × setPaintProperty on one layer, one per frame	<Layer> renders	6,000	0
	<Source> renders	200	0
	React render time	5.5 ms	0 ms
	main-thread script time	84.5 ms	75.0 ms
mapStyle swap	all 120 layers back after	25.2 ms	25.7 ms

Main-thread script time is mostly MapLibre's own work, so on a fast machine its drop varies between runs: −1 % to −17 % over four runs. The saved render time grows with the number of layers and on slower devices. In an editor with 121 layers that adds marker images on demand, one load fired 51 styledata events and 3,525 <Layer> renders; with this change those renders are gone.

Benchmark (before/after, runs with two checkouts of this repo): https://gist.github.com/tordans/964b42fdd89d39c1dfaf98d7419cf6a7

Validation: TypeScript build, yarn lint, and all 86 node/headless tests pass.

---

Note

Medium Risk
Touches map style sync for core Source/Layer components; behavior is narrowed but style swaps and missing-layer recovery must stay correct.

Overview
Stops <Source> and <Layer> from re-rendering on every map styledata event (e.g. addImage, setPaintProperty), which previously caused large apps with many layers to re-render unnecessarily.

The styledata handler now calls forceUpdate only when recovery is needed: <Layer> when the layer id is absent from a loaded style; <Source> when the source is missing or is not the same instance children were rendered with (sourceRef), including after a style swap or a colliding source id in the style. The same logic is applied in react-mapbox and react-maplibre.

Tests assert zero profiler renders after unrelated style mutations, that externally removed layers are re-added, and that layers still mount when the initial style already defines the source.

^{Reviewed by Cursor Bugbot for commit 09816b1. Bugbot is set up for automated code reviews on this repo. Configure here.}

[greptile-apps]

Confidence Score: 5/5

[Medium impact] The PR appears safe to merge; no actionable new issues were found.

Summary

Reduces unnecessary renders after map style changes in both packages.

• Sources and layers render again only when their map entries need recovery.

_{Reviews (2) · Last reviewed commit: "fix: re-render Source when the style has..." · Reviewed by Greptile}

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Cursor Bugbot has reviewed your changes using default effort and found 1 potential issue.

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