feat: show basemap thumbnails in the Basemaps panel - #2089
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The catalog lists OSM, OpenTopoMap, and similar rasters as name-only rows. Stamp each raster entry with a z=2 XYZ tile so they can be told apart before clicking. Style basemaps have no single-tile endpoint and are left unchanged. Failed tile loads drop the image instead of showing a broken icon.
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📝 WalkthroughWalkthroughThe basemap control now adds raster thumbnails and generated style previews to result rows. It filters unsupported sources, renders visible style previews with a hidden MapLibre camera, observes row changes, and manages pause and disposal cleanup. Desktop styles define the thumbnail layout and appearance. ChangesBasemap thumbnail previews
Estimated code review effort: 4 (Complex) | ~45 minutes Merge Risk: ⚪ Minimal · up to The change adds basemap thumbnails with localized UI behavior and no actionable merge-blocking risk remains. Sequence Diagram(s)sequenceDiagram
participant MapLibreBasemapControl
participant BasemapThumbnailInstaller
participant BasemapResultRow
participant HiddenMapLibreCamera
MapLibreBasemapControl->>BasemapThumbnailInstaller: Install thumbnail enhancement
BasemapThumbnailInstaller->>BasemapResultRow: Observe and enhance result rows
BasemapThumbnailInstaller->>BasemapResultRow: Mark raster or style preview state
BasemapThumbnailInstaller->>HiddenMapLibreCamera: Capture visible style snapshot
HiddenMapLibreCamera-->>BasemapResultRow: Apply JPEG preview
MapLibreBasemapControl->>BasemapThumbnailInstaller: Pause or dispose on lifecycle change
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Raster rows still use a z=2 XYZ tile. Keyless style rows first show the style background color, then a small offscreen MapLibre snapshot of Europe once the row is on screen. Applying a style pauses the hidden map so it does not compete with the live view. Styles that still have an API-key placeholder are skipped.
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Actionable comments posted: 1
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Inline comments:
In `@packages/plugins/src/plugins/maplibre-basemap-control.ts`:
- Around line 199-201: Update the MutationObserver setup around enhance so
subsequent mutations only scan affected basemap rows instead of traversing the
full document. Observe the basemap control container or process
MutationRecord.addedNodes to identify added rows and descendants, while
preserving the initial enhance() scan for rows already present.
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apps/geolibre-desktop/src/index.csspackages/plugins/src/plugins/maplibre-basemap-control.ts
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Pull request overview
Adds lightweight raster basemap previews in the Basemaps panel by injecting a small z=2 tile thumbnail into each raster basemap row (while leaving style/vector-style basemaps unchanged), plus minimal CSS to lay out and theme the thumbnail.
Changes:
- Add a DOM “thumbnail enhancer” that finds basemap rows and prepends an
<img>preview for raster basemaps (removing it on load failure). - Cache the control’s basemap catalog so previews can be resolved by
data-basemap-id. - Add CSS to allocate a thumbnail column and style the preview image.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
packages/plugins/src/plugins/maplibre-basemap-control.ts |
Adds thumbnail URL building and a MutationObserver-based DOM enhancer to inject raster previews into basemap rows. |
apps/geolibre-desktop/src/index.css |
Adds layout/styling for the injected thumbnail inside basemap result rows. |
Suppressed comments (1)
packages/plugins/src/plugins/maplibre-basemap-control.ts:203
- The thumbnail enhancer’s MutationObserver is currently attached to
document.body, so any DOM update in the app (not just the Basemaps panel) triggersenhance()and a document-wide query. This is avoidable work and can become a noticeable performance cost in a store-driven UI.
Consider scoping the observer to the Basemaps control root when present, and throttling callbacks so multiple mutations coalesce into one enhance() run per frame.
// the reopened panel highlights them as active and a re-click on a stacked
// raster removes it. Without the raster ids the new instance only knows the
// style basemap and shows restored overlays as inactive. When rasters are
// stacked the map is in overlay mode, so restore that too.
const activeStyleId = getBasemapIdForStyleUrl(app.getActiveBasemap());
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Actionable comments posted: 6
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Inline comments:
In `@packages/plugins/src/plugins/basemap-thumbnails.ts`:
- Around line 164-186: Update installBasemapThumbnails and its enhance/observer
setup to resolve .basemap-control-panel lazily after the control is added, or
defer observer installation until that panel exists. Do not use document.body as
a fallback for mutation or intersection observation; scope both observers to the
actual panel and avoid rebuilding the catalog from unrelated document mutations.
- Around line 28-49: Update styleSwatch so failed or null results remove the
corresponding URL from swatchCache before returning null, allowing later calls
to retry transient fetch failures while preserving caching for successful
swatches.
- Around line 134-145: Update stamp to attach an image error handler that
removes the failed thumbnail and marks its containing row so the CSS placeholder
applies. Handle failures for both newly created and existing images while
preserving the current successful image-update behavior.
- Around line 8-10: Update needsKey to detect any unresolved brace-delimited
template placeholder rather than only api-key, access_token, and key, so
placeholders such as aws-region are rejected before styleSwatch fetches the URL.
- Around line 93-116: Update the job created in the snapshot flow to listen for
the map error event and call finish(null) immediately when setStyle fails, while
preserving cleanup of both the style-load and error listeners along with the
existing timeout behavior. Anchor the change to the finish callback, onLoad
handler, and map.setStyle call so failed styles no longer wait for the full
timeout.
- Around line 121-126: Update the pause/resume lifecycle in the thumbnail
controller’s pause() implementation so paused remains true after teardown until
an explicit resume or equivalent post-style-settle signal clears it; remove the
immediate reset within pause(), and ensure the existing observer/job scheduling
respects this state to prevent hidden-map recreation during basemap changes.
Apply the same fix in `@packages/plugins/src/plugins/maplibre-basemap-control.ts`
at line 338: The call site is valid; the defect is that pause() clears its state
synchronously.
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- Reject any unresolved `{...}` placeholder instead of three hardcoded key
names, so a provider token the control substitutes (`{aws-region}`) or a tile
scheme this module does not fill in (`{quadkey}`, `{-y}`) is skipped rather
than fetched literally.
- Drop a failed style-swatch fetch from `swatchCache` so a transient network
error is not cached for the life of the page.
- Finish a snapshot immediately on a map `error` raised before `style.load`, so
an unreachable style no longer holds the serialized queue for the full 6s
timeout. Errors after the style loaded are tile failures and are ignored.
- Make `pause()` actually pause: a promise gate the queued jobs await, reopened
on resume or after a bounded delay, replacing a flag that was reset
synchronously before any job could observe it. Queued rows now wait rather
than resolving null and losing their thumbnail.
- Remove a thumbnail whose image fails to load and mark the row skipped, so a
404 raster tile falls back to the name-only row instead of the browser's
broken-image glyph.
- Scope both observers to the control's own panel, never `document.body`, and
re-resolve the panel when the control rebuilds it (a position change), which
previously left the observers watching a detached node.
- Rank the preview states so a slow flat-colour swatch cannot downgrade a row
that already shows the real render.
- Name the mirrored `maplibre-gl-basemap-control` DOM contract in exported
constants with a re-check-on-bump note, and add a test that builds a real
control and fails if the panel/row/id attribute drift. Documented in
CLAUDE.md alongside the other unexported-internal mirrors.
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Inline comments:
In `@packages/plugins/src/plugins/basemap-thumbnails.ts`:
- Around line 48-50: Update hasUnresolvedPlaceholder and the styleUrlOf
validation so every brace-delimited placeholder is rejected for style URLs,
while rasterPreviewUrl continues allowing supported tile tokens such as {s}; add
coverage for a {s} placeholder in a style URL.
- Around line 211-216: Update the snapshot job lifecycle around the installer’s
timeout and delayed capture callback to track its cancellation function, clear
both timers, and settle the active job from dispose(). Guard the completion path
before paint() so disposed installers cannot capture from or update the
torn-down map; ensure deactivate() fully releases these runtime resources.
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CLAUDE.mdpackages/plugins/src/plugins/basemap-thumbnails.tstests/basemap-thumbnails.test.ts
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- Settle the in-flight snapshot when the hidden map is torn down. Its listeners were bound to the removed map, so it could only resolve through the 6s timeout, and since jobs are serialized that stalled every later preview well past PAUSE_MS. Regression from the previous commit, which stopped resetting the queue in pause(). - Flip the preview row index for a `tms` raster source (the catalog ships two), which otherwise previewed the vertically mirrored tile. - Fall back to the name-only row when a style preview produces nothing, so an unreachable style host degrades the way a failed raster tile already did instead of keeping its placeholder for good. - Reject every placeholder in a style URL, not just the ones a raster template substitutes — a style URL is fetched verbatim. - Clear the delayed capture timer in `finish` and ignore a preview that resolves after `dispose()`, so a deactivated plugin runs no callback and repaints no row. - Watch the map container's child list rather than the whole document body once the panel has been seen; the control appends its panel there, so a rebuilt panel is still caught without observing every application mutation. - Cover the tms and style-placeholder rules, and assert the panel stays a direct child of the map container, which the narrowed watch now depends on.
| // survive a new session). | ||
| relinkRestoredRasterBasemaps(); | ||
| thumbnails?.dispose(); | ||
| thumbnails = installBasemapThumbnails(basemapControl); |
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activate() correctly disposes and reinstalls thumbnails after addMapControl, because (per the comment in basemap-thumbnails.ts's watchForPanel) "the control builds a fresh panel element in every onAdd".
setMapControlPosition (further down, unchanged by this PR) does the same removeMapControl + addMapControl cycle on the same basemapControl instance to move it to a new corner, but never touches thumbnails. Since installBasemapThumbnails's bootstrap/scoped MutationObservers are anchored to the old panel and its now-detached parent, and the remove/re-add doesn't mutate that old subtree in a way either observer would see, the freshly created panel is never discovered — enhance() never runs for it, so thumbnails silently stop appearing (and the old observers/panel leak) after the user repositions the Basemaps control from the Plugins menu, until the plugin is deactivated and reactivated.
Worth adding the same thumbnails?.dispose(); thumbnails = installBasemapThumbnails(basemapControl); after the addMapControl call in setMapControlPosition.
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Disagreeing on this one, with a test rather than an argument — but the underlying risk was real enough to pin, so 5fb7d7b adds a regression test for exactly this cycle.
The premise is that both observers are anchored to the old panel. scoped is, but bootstrap is not: watchForPanel observes panel.parentElement. onAdd does this._mapContainer = map.getContainer(); this._mapContainer.appendChild(this._panel), and onRemove does this._panel.parentNode.removeChild(this._panel) — so the panel is a direct child of the map container, that container element is reused across the cycle, and both the removal and the insertion are childList mutations on the very node bootstrap watches. They also batch into one callback, since setMapControlPosition does them synchronously, by which point querySelector already returns the new panel.
The new test in tests/basemap-thumbnails.test.ts drives a real BasemapControl through onRemove() + onAdd() and asserts the rebuilt panel gets its thumbnail back. It fails if watchForPanel is anchored to the panel instead of its parent, which I checked. I would rather have that guarantee under test than duplicate the install in setMapControlPosition, since the observer path also covers any other route that rebuilds the panel.
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- Return null instead of rejecting when the hidden map cannot be constructed (WebGL context failure), so a snapshot failure degrades like every other one here rather than surfacing as an unhandled rejection. - Add a regression test for the reposition cycle: install thumbnails, run the control's onRemove/onAdd pair, and assert the rebuilt panel is enhanced again. Verified it fails if the watch is anchored to the panel instead of its parent.
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- Bound the style-swatch fetch with AbortSignal.timeout on the same budget the snapshot path already used. A host that accepts the connection but never answers left the promise unsettled and the row on its placeholder for good. - Defer the raster tile request and the style JSON fetch to the same IntersectionObserver that already gated the full snapshot, so opening the Basemaps panel contacts only the providers whose rows are on screen instead of every host in the catalog at once. Rows fall back to previewing immediately where no IntersectionObserver exists. - Split the rank check out of `paint` so the raster path applies it to the row it already holds rather than re-querying the document by id. - Cover the deferral with a test that drives a stub IntersectionObserver.
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- Reuse a snapshot already queued for the same style url. `snapCache` only fills in once a job resolves, so a second request before then queued a redundant full style load; this is the reuse `styleSwatch` already gets from caching its in-flight promise. - Add a test asserting no preview url can carry a configured credential. Previews fire on scroll rather than on an explicit pick, so reaching a keyed endpoint would spend the user's quota. The control keeps the catalog's raw templates and substitutes only when a basemap is applied, so keyed entries are already rejected — the test fails if that stops being true.
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| /** Repaint by id, for a preview that resolved long after the row was scanned. */ | ||
| function paint(id: string, src: string, state: string): void { |
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Minor/low confidence. paint/markSkipped (and rowSelector) query document.querySelectorAll rather than scoping to the tracked panel element, even though the enclosing closure already holds panel. Functionally harmless today since data-basemap-id only appears on basemap rows, but it means every async preview resolution re-scans the whole document instead of the panel subtree. Could pass panel into these (or make them closures inside installBasemapThumbnails) for a cheaper, more clearly-scoped query — not worth blocking on.
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Not taking this one, but thanks for flagging it — and you are right that it is not worth blocking on.
paint and markSkipped run from callbacks that resolve long after the row was scanned, and the panel can be rebuilt in between (onAdd builds a fresh one, which setMapControlPosition triggers). Querying the document means a preview that lands mid-rebuild still finds the current row; scoping to the tracked panel would make that case silently paint nothing. The cost is a document-wide querySelectorAll a handful of times per panel open, now that previews are gated on visibility — cheaper than the correctness edge it would buy back.
Leaving this open rather than resolving it, in case you or a maintainer sees the tradeoff differently.
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- Extract the never-move-a-row-backwards rule into an exported `advances`, and cover it directly. It was the trickiest invariant in the preview code and was only reachable through a race that no test could stage. - Add a test for the style path: a row whose swatch and snapshot both fail must fall back to the name-only layout without rejecting. Verified it fails if the snapshot's try/catch is removed, so it pins the WebGL-failure fix too.
giswqs
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This is a great addition. Thank you for your contribution.
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| .basemap-control-result[data-geolibre-basemap-preview="pending"]:not( | ||
| :has(.geolibre-basemap-thumbnail) | ||
| )::before { | ||
| content: ""; | ||
| width: 56px; | ||
| height: 42px; | ||
| border-radius: 3px; | ||
| background: hsl(var(--muted)); | ||
| } |
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Quality (medium confidence): the real thumbnail (.geolibre-basemap-thumbnail, below) pins itself to grid-row: 1 / span 3 so it spans the row's full height regardless of how many text lines are next to it. This ::before "pending" placeholder is the same size (56×42) but doesn't set grid-row, so it will fall into the grid's default auto-placed cell instead of spanning all 3 rows like the thumbnail it's standing in for. If the row's other grid items span multiple rows too, the placeholder box and the eventual thumbnail likely won't occupy the same visual footprint, causing a layout shift when the pending placeholder is replaced by the real <img>.
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| /** | ||
| * `BASEMAP_PANEL_SELECTOR` / `BASEMAP_ROW_SELECTOR` / `BASEMAP_ROW_ID_ATTR` | ||
| * mirror DOM that `maplibre-gl-basemap-control` renders but does not export, so | ||
| * nothing but this file notices if a bump renames one — the queries would just | ||
| * stop matching and thumbnails would silently stop appearing. Rather than | ||
| * restate the strings, this builds a real `BasemapControl` and asks it for its | ||
| * rendered panel. | ||
| */ | ||
| describe("the preview state rank", () => { |
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Quality (high confidence): this JSDoc block describes BASEMAP_PANEL_SELECTOR/BASEMAP_ROW_SELECTOR/BASEMAP_ROW_ID_ATTR and how the DOM-mirror tests work, but it's placed directly above describe("the preview state rank", ...), which tests advances() and has nothing to do with those selectors. It reads like it was meant to sit above describe("the maplibre-gl-basemap-control DOM mirror", ...) further down (line 165), which is the block that actually builds a real BasemapControl and asserts against the selectors. Purely a doc/readability nit — the tests themselves are correct — but worth moving so the comment sits next to the code it explains.
Separately, style() (line ~52) and styleBasemap() (line ~38) are identical helper functions with different names — could drop one and use it in both places.
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The core logic — the state-ranking/ |
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The Basemaps panel listed every catalog entry as a name-only row.
2/1/1).Uses
getBasemaps()anddata-basemap-idonly.Summary by CodeRabbit
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