Zig API

The engine is a real Zig package named tile57 (v0.1.0, requires Zig 0.16). Add it as a dependency and @import("tile57") for the curated public surface (src/tile57.zig). The C ABI is a thin shim over this same API.

The high-level engine: Chart

Open a chart from bytes, a path, or cells, then fetch tiles by (z, x, y):

const tile57 = @import("tile57");

// A PMTiles archive, or a raw S-57 cell portrayed live (auto-sniffed).
var chart = try tile57.Chart.openBytes(cell_bytes, .auto, null);
defer chart.deinit();

if (try chart.tile(z, x, y)) |mvt| {     // decompressed MVT bytes, or null if empty
    defer tile57.freeBytes(mvt);
    // … hand to your renderer …
}

Chart methods:

Method	Purpose
openBytes(bytes, format, rules_dir)	open one chart from bytes (PMTiles or S-57 cell).
openPath(path, rules_dir, pick_attrs)	open an on-disk ENC_ROOT dir (or a single .000) as a streaming chart.
openCells(cells, rules_dir, pick_attrs)	open a multi-cell ENC_ROOT from bytes (each cell's .001… updates applied).
openCellsStreaming(metas, reader, user, rules_dir, pick_attrs)	low-memory ENC_ROOT: read each cell's bytes on demand, free on eviction.
tile(z, x, y) -> ?[]u8	the tile's decompressed MVT bytes (null = empty).
bounds() -> ?[4]f64	geographic extent [w, s, e, n], if known.
anchor()	a good initial camera (lat, lon, zoom) on real data.
bands() -> u32	bitmask of navigational bands present.
zoomRange()	the min/max zoom the chart serves.
scamin() -> ![]u32	the distinct SCAMIN denominators present (the live SCAMIN manifest).
format() -> Format	the resolved backend (after .auto).
clearCache()	drop the in-memory tile cache.
deinit()	release the chart and its cached tiles.

tile57.Format is .auto / .pmtiles / .s57_cell. rules_dir is the S-101 portrayal rules directory for live S-57 cells; null (or "") uses the rules embedded in the binary (or TILE57_S101_RULES if set), so no on-disk catalogue is required; a path overrides with an on-disk catalogue. Free any bytes returned by tile / bakeArchive with tile57.freeBytes.

The streaming open uses the extern types tile57.CellMeta (bbox + cscl), tile57.CellBytes (the cell's base + updates, ownership transferred to the library), and tile57.CellReadFn (the reader callback). Multi-cell input for openCells is tile57.CellInput.

Bake an ENC_ROOT

// Band-streamed: peak memory tracks the largest single band, not the whole archive.
const pmtiles_bytes = try tile57.bakeArchive(/* … */);
defer tile57.freeBytes(pmtiles_bytes);

tile57.bakeArchive bakes a whole ENC_ROOT into one PMTiles archive, zoom-banded per cell by compilation scale; tile57.Progress is the optional progress callback type.

Style + portrayal assets

// MapLibre style from a template + mariner S-52 display settings + colortables.
const json = try tile57.style.build(/* … */);     // tile57.style.Mariner settings

Surface	What it does
tile57.style.build (chartstyle.buildStyle)	patch a MapLibre style template with mariner settings + colortables.
tile57.style.Mariner	the S-52 mariner display options struct.
tile57.assets	colortables / linestyles / style.json / manifest generation.
tile57.sprite	S-101 sprite + area-fill pattern atlases (SVG raster).
tile57.chartstyle	the mariner-driven style-patching module.

Tiling + encoding

The mid-level packages, for callers that compose their own pipeline:

Module	Role
tile57.mvt	Mapbox Vector Tile encode/decode
tile57.tile	web-mercator tiling + clipping
tile57.pmtiles	PMTiles read/write
tile57.bake_enc	banded multi-cell ENC_ROOT → PMTiles
tile57.s57_mvt	S-57 feature → MVT tile

Raw formats (advanced)

The pure-Zig foundational parsers under tile57.formats:

Module	Role
tile57.formats.iso8211	ISO/IEC 8211 records
tile57.formats.s57	S-57 ENC cell parser + geometry
tile57.formats.s100	S-100/S-101 catalogue + adaptation

tile57.version is the package version string ("0.1.0"), matching build.zig.zon and tile57_version().