OPFS-based offline-first PMTile basemaps

[spwoodcock]

What type of PR is this? (check all applicable)

• 🍕 Feature
• 🐛 Bug Fix
• 📝 Documentation Update
• 🎨 Style
• 🧑‍💻 Code Refactor
• 🔥 Performance Improvements
• ✅ Test
• 🤖 Build
• 🔁 CI
• 📦 Chore (Release)
• ⏩ Revert

Related Issues

None

Describe this PR

• Started work on loading PMTile files into browser OPFS storage, then reading when offline.

Finished

• Loading the PMTiles archive into OPFS.
• Reading the PMTiles into OPFS.
• Parsing the PMTiles file as a PMTiles object.

To Do

• Assess if the user is offline or not (likely via PWA functionalities).
• If user is offline, load the tiles from OPFS to render.
• Render the PMTiles in OpenLayers.

@varun2948 @NSUWAL123

Notes

• OPFS is unique per domain, so there is no chance of file mixup.
• The pmtile archives are for the entire project area, stored under PROJECT_ID/all.pmtiles.

Screenshots

• The lightning bolt icon button will download the tiles to OPFS, instead of download directory on filesystem.

Checklist before requesting a review

• 📖 Read the FMTM Contributing Guide: https://github.com/hotosm/fmtm/blob/main/CONTRIBUTING.md
• 📖 Read the FMTM Code of Conduct: https://github.com/hotosm/fmtm/blob/main/CODE_OF_CONDUCT.md
• 👷‍♀️ Create small PRs. In most cases, this will be possible.
• ✅ Provide tests for your changes.
• 📝 Use descriptive commit messages.
• 📗 Update any related documentation and include any relevant screenshots.

[optional] What gif best describes this PR or how it makes you feel?

[varun2948]

Looks good, now we have to test it in dev inorder to confirm if everything is fine or not !

[spwoodcock]

Works locally for me! Great work, merging 👍
Part of the fix seems to be not using a WebGL layer - to be investigated in the future!