SwiftJWW

A native-Swift reader for JWW — the native drawing format of Jw_cad, the free 2D CAD program widely used in Japan — plus a jww2dxf command-line converter.

JWW is an MFC CArchive-serialized binary file: a JwwData. magic, a version, a large (version-gated) document header, then an MFC object array of drawing entities. SwiftJWW reads the geometry — lines, arcs/circles/ellipses, points, and text — into a neutral Drawing and converts it to DXF.

• Pure Swift, no third-party dependencies.
• Clean-room port of the documented JWW byte layout (the published jwdatafmt spec + LibreCAD’s jwwlib as the reference reader). Validated byte-for-byte against the reference reader on real drawings (JWW v7.00): identical entity counts and bounding boxes across thousands of entities.

Installation

dependencies: [
    .package(url: "https://github.com/SecondMouseAU/SwiftJWW.git", from: "1.0.0"),
],

.target(name: "YourTarget", dependencies: [.product(name: "SwiftJWW", package: "SwiftJWW")]),

Command line

swift run jww2dxf drawing.jww            # → drawing.dxf
swift run jww2dxf drawing.jww out.dxf

Prints a one-line summary (version, entity counts, bbox) and writes the DXF.

Library

import SwiftJWW

let dwg = try JWW.read(contentsOf: url)
print(dwg.version, dwg.counts, dwg.bounds as Any)

for e in dwg.entities {
    switch e {
    case let .line(a, b, layer, color): break
    case let .arc(center, radius, start, sweep, tilt, ratio, full, layer, color): break
    case let .point(at, layer, color): break
    case let .text(at, height, width, angleRad, raw, layer, color): break
    }
}

let dxf = DXFWriter.string(dwg)          // or: try DXFWriter.write(dwg, to: url)

JWW.looksLikeJWW(data) sniffs the JwwData. signature.

Model

enum Entity {
    case line(a: Point, b: Point, layer: Int, color: Int)
    case arc(center: Point, radius: Double, start: Double, sweep: Double,
             tilt: Double, ratio: Double, full: Bool, layer: Int, color: Int)   // start/sweep radians
    case point(at: Point, layer: Int, color: Int)
    case text(at: Point, height: Double, width: Double, angleRad: Double,
              raw: [UInt8], layer: Int, color: Int)                              // raw = CP932 bytes
}

Drawing.counts exposes per-class counts (line / arc / point / text / solid / block / dim) for verification against reference tools; Drawing.bounds gives the drawing extent.

DXF mapping

Output is an entities-only, version-agnostic ASCII DXF accepted by AutoCAD, LibreCAD, and most CAD tools. JWW pen colours pass through as AutoCAD Color Index values; JWW layer numbers become DXF layer names.

Scope & notes

Covers lines, arcs/circles/ellipses, points, text, block definitions + inserts, and dimensions. Block definitions are exposed on Drawing.blocks (keyed by number) and emitted as DXF BLOCKs, with .insert entities becoming INSERTs; dimensions are decomposed into their drawn parts. The line/arc/point/text core is validated byte-for-byte against the reference reader on real drawings; block/dimension support is validated on synthetic fixtures (real block-bearing test files welcome).

Text encoding. JWW stores text as CP932 (Shift-JIS) bytes; Entity.text exposes the raw bytes, and the DXF writer decodes them to Unicode using the system’s CoreFoundation encoding tables. That’s reliable on Apple platforms; on Linux (swift-corelibs-Foundation) CP932 may be unavailable, so Japanese text may not decode — the geometry still converts. To stay fully portable, decode raw yourself with a vendored Shift-JIS table.

DWG is out of scope (proprietary). Produce DXF here and convert to DWG downstream (e.g. the free ODA File Converter) if you need it.

License & provenance

MIT. This is a clean-room reimplementation of the JWW byte layout — no jwwlib source is included. JWW and Jw_cad are the work of their respective authors; LibreCAD’s jwwlib (GPL) and the published jwdatafmt specification were used as format references.