MapLibre Tile support pulls in the maplibre-tile-spec submodule and needs
cmake to build it, which is a lot to ask of anyone who only wants to work
with Mapbox Vector Tiles.
`make MLT=0` compiles with -DNO_MLT, skips the submodule and its cmake
build entirely, and drops the MLT tests from `make test`. The result needs
no dependencies beyond the ones MVT already needed, and can be built from
a checkout with no submodules at all.
Everything that touches the MLT library is behind the #ifdef, which is
just the two files that were written for it. The option parsing and the
tile format helpers stay compiled either way, so nothing else needs to
know: --output-format=mlt reports that the build has no MLT support rather
than being an unrecognized value, and a tile that is recognized as MLT
reports the same instead of being misparsed as a protobuf, since the
format sniffing itself doesn't need the library.
CI builds and tests this configuration from a checkout without submodules,
so it can't quietly stop working.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LxhELiLtpUFwrPSWwTYdHG
Tilesets written with --output-format=mlt could not be read back by any of
tippecanoe's own tools, which made MLT a dead end rather than a tile format.
Build the mlt-cpp decoder from the vendored maplibre-tile-spec submodule
alongside the encoder, and convert a decoded MapLibre Tile back into the
equivalent mvt_tile: geometry, feature ids, and property columns. MLT rings
come back explicitly closed, so the repeated final point becomes an MVT
closepath, and the property columns, which are held in an unordered map,
are sorted by name so that the attributes of a decoded tile come out in a
stable order.
Rather than adding an option to each tool, mvt_tile::decode() detects the
encoding and dispatches, so everywhere tippecanoe already reads a vector
tile can read MLT. An MLT tile begins with a varint layer length followed
by a varint layer tag whose only defined value is 1, while an MVT tile is
a protobuf whose only field is the repeated layer field 3, so it begins
with 0x1a followed by a layer length that can never be as short as the one
byte that would be needed to look like an MLT layer tag.
Tile directories also needed a fix: enumerate_dirtiles() recognized .mlt
file names but still recorded .pbf as the extension to read them back
with, so decoding an MLT directory failed to find any of its tiles.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LxhELiLtpUFwrPSWwTYdHG
Claude