Offline (mbgl-core implementation)

[jfirebaugh]

TODO list:

• Normalize Mapbox tile URLs to mapbox://tiles scheme before requesting, translate back to api.mapbox.com URLs inside OnlineFileSource.
• Remove sqlite_cache.{hpp,cpp}
• Style, source, sprite, glyphs downloading
• Figure out progress semantics when complete file count is indeterminate
• Font stack normalization
• Verify that LatLngBounds enforces the correct invariants: LatLng and LatLngBounds should enforce invariants #3802
• Tiles downloading
• Tile ID wrapping
• Region deletion
• Test cases
  • No sprite
  • No glyphs
  • Inline source
  • GeoJSON source
• Size reporting
• Remove schema version logic; once shipped we need to write migrations rather than dumping existing dbs
• Review use of Request::Error::NotFound
• Get status of inactive download
• Error handling
• Resource deletion
• Concurrency
• Performance
  • Concurrent request throttling
  • [ ] Request pipelining
  • Add indexes
• Size limits / eviction
• Polish schema
• Consistently use ?NNN syntax for prepared statements

Think about

• Style spec migrations -- After we release v9, we'll need to continue supporting offline databases containing v8 styles, via version branches in the renderer, or JIT migration.
• Static evaluation of font stacks vs. data driven styling -- The required font stacks need to be determined without loading data. Therefore we should either not support data-driven "text-font", or require that all possible font stacks values be listed elsewhere, like we do with "icon-image".
• Stop tile pyramid recursion when encountering a nodata tile -- This is an potential future optimization to avoid storing nodata child tiles once we encounter a nodata parent. This depends on Overzoom cached/offline tiles #123.

[jfirebaugh]

Notes from the "Think about" section:

• Style spec migrations -- After we release v9, we'll need to continue supporting offline databases containing v8 styles, via version branches in the renderer, or JIT migration.
• Static evaluation of font stacks vs. data driven styling -- The required font stacks need to be determined without loading data. Therefore we should either not support data-driven "text-font", or require that all possible font stacks values be listed elsewhere, like we do with "icon-image".
• Stop tile pyramid recursion when encountering a nodata tile -- This is an potential future optimization to avoid storing nodata child tiles once we encounter a nodata parent. This depends on Overzoom cached/offline tiles #123.

[bsudekum]

Congrats 🎉!