feat: topo-dark style variant + fix font glyph loading

[fank]

Summary

• Add topo-dark MapLibre style variant with dark background (#1B1B1B), muted colors (sea #1a3a5c, contours #5a4a3a/#3a5a7a, roads #888888, forest #3a5a2a), light-on-dark labels with #111111 halos, and stronger hillshade (0.5 exaggeration, 0.6 shadow)
• Refactor topo style to use dedicated knownTopoLayerStyles map and topoLayerOrder render order instead of reusing color-relief's buildVectorFeatureLayers
• Fix MapLibre font glyph 404s (GET /fonts/OpenSans-Regular/0-255.pbf 404) by adding transformRequest to rewrite glyph URLs to the correct images/maps/fonts/ server path — avoids fragile relative URL resolution from the style JSON location

Changes

• internal/maptool/styles.go — StyleTopoDark constant, knownTopoDarkLayerStyles map, buildTopoDarkLayers/buildTopoDarkVectorFeatureLayers, topo style refactor with knownTopoLayerStyles/topoLayerOrder/buildTopoVectorFeatureLayers
• internal/maptool/metadata.go — generate topo-dark.json style file
• internal/maptool/styles_test.go — add StyleTopoDark to variant test loop
• static/scripts/ocap.js — add Topo Dark style candidate, add transformRequest for font glyph URL rewriting

Test plan

• go build ./...
• go test ./internal/maptool/
• Browser test: verify topo-dark style renders with dark background and muted colors
• Browser test: verify font glyphs load without 404 errors for all style variants
• Browser test: verify style switcher shows Topo Dark button when style file exists

[gemini-code-assist]

Summary of Changes

Hello @fank, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a new "topo-dark" map style variant, providing users with an alternative dark-themed topographic map. Alongside this new feature, the existing topographic style's layer management has been improved for clarity and maintainability. Crucially, it also addresses a client-side issue where MapLibre font glyphs were failing to load due to incorrect URL resolution, enhancing the robustness of map rendering across all styles.

Highlights

• New Map Style: Introduced a "topo-dark" MapLibre style variant with a dark background (#1B1B1B), muted colors for geographical features (sea, contours, roads, forest), light-on-dark labels, and stronger hillshade (0.5 exaggeration, 0.6 shadow).
• Topo Style Refactoring: The existing "topo" style was refactored to use dedicated knownTopoLayerStyles and topoLayerOrder maps, improving organization and rendering control by moving away from reusing buildVectorFeatureLayers.
• Font Glyph Loading Fix: Resolved 404 errors for MapLibre font glyphs by implementing a transformRequest function in ocap.js to correctly rewrite glyph URLs to the images/maps/fonts/ server path, ensuring proper font rendering across all map styles.

Changelog

• internal/maptool/metadata.go
  • Added StyleTopoDark to the list of styles to be generated, ensuring topo-dark.json is created.
• internal/maptool/styles.go
  • Introduced new helper functions (topoContourColorExpr, topoTextLayout, topoTextPaint, topoDarkContourColorExpr, topoDarkTextPaint, makeTopoDarkLabel) to define specific styling for both standard topo and the new topo-dark variant.
  • Defined knownTopoLayerStyles and topoLayerOrder to centralize and manage the rendering of layers for the standard topo style.
  • Defined knownTopoDarkLayerStyles with dark-themed colors and properties for the new topo-dark style.
  • Added StyleTopoDark to the StyleVariant enum.
  • Modified GenerateStyleDocument to set the appropriate background color (#1B1B1B) and call the new buildTopoDarkLayers function for the StyleTopoDark variant.
  • Refactored buildTopoLayers to use the new knownTopoLayerStyles and topoLayerOrder for building vector feature layers.
  • Implemented buildTopoDarkLayers and buildTopoDarkVectorFeatureLayers to construct the layers for the new dark style, applying its specific color palette and hillshade settings.
• internal/maptool/styles_test.go
  • Updated the test loop for style variants to include StyleTopoDark, ensuring its generation is tested.
• static/scripts/ocap.js
  • Added a "Topo Dark" entry to the styleCandidates array, making the new style selectable in the UI.
  • Implemented a transformRequest function within the L.maplibreGL initialization to intercept and correct font glyph URLs, resolving 404 errors by pointing them to the correct images/maps/fonts/ path.

Activity

• No specific human activity (comments, reviews, progress updates) was provided in the context for this pull request.

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[gemini-code-assist]

Code Review

This pull request introduces a new topo-dark map style variant, refactors the existing topo style generation for better separation and maintainability, and fixes an issue with font glyph loading in MapLibre. The changes are well-structured and address the goals outlined in the description. I've provided a couple of suggestions to reduce code duplication in the new style generation logic, which would further improve the code's maintainability.

[github-actions]

Merging this branch will increase overall coverage

Impacted Packages	Coverage Δ	🤖
github.com/OCAP2/web/internal/maptool	13.87% (+0.69%)	👍

---

Coverage by file

Changed files (no unit tests)

Changed File	Coverage Δ	Total	Covered	Missed	🤖
github.com/OCAP2/web/internal/maptool/metadata.go	11.08% (ø)	352	39	313
github.com/OCAP2/web/internal/maptool/styles.go	33.12% (-0.87%)	921 (+253)	305 (+78)	616 (+175)	👎

Please note that the "Total", "Covered", and "Missed" counts above refer to code statements instead of lines of code. The value in brackets refers to the test coverage of that file in the old version of the code.

Changed unit test files

• github.com/OCAP2/web/internal/maptool/styles_test.go