SwiftDXF

A small, dependency-free Swift reader for ASCII DXF — AutoCAD's Drawing Interchange Format — that lifts model-space 2D geometry into a neutral, Sendable value model. Clean-room, MIT-licensed, and validated bit-for-bit against the MIT-licensed ezdxf reference reader.

import SwiftDXF

let dwg = try DXF.read(contentsOf: url)
print(dwg.version)          // e.g. "AC1009" (R12)
print(dwg.counts.total)     // entities read
for case let .line(a, b, layer, _) in dwg.entities {
    print(layer, a, b)
}

What it reads

The 2D entity set that dominates real-world drawings, from the ENTITIES (model-space) section:

DXF entity	DXF.Entity case
LINE	.line(a, b, layer, color)
CIRCLE	.circle(center, radius, …)
ARC	.arc(center, radius, startDeg, endDeg, …)
ELLIPSE	.ellipse(center, majorAxis, ratio, startParam, endParam, …)
POINT	.point(at, …)
TEXT, MTEXT	.text(at, height, rotationDeg, string, …)
LWPOLYLINE, POLYLINE/VERTEX	.polyline(vertices, closed, …) — each vertex carries its bulge

Entities it does not model (e.g. INSERT, SPLINE, HATCH, DIMENSION) are skipped, not fatal.

Drawing also exposes header essentials: version ($ACADVER), insUnits ($INSUNITS), and the declared extMin / extMax extents ($EXTMIN / $EXTMAX), plus a computed bounds over the entities actually read.

Behaviours worth knowing

• Encoding. Files are decoded as UTF-8 when valid, otherwise CP932 / Shift-JIS — the common code page for DXF exported by Japanese CAD tools (e.g. Jw_cad). Because CP932 is an ASCII superset, the group-code structure is unaffected either way. AutoCAD \U+XXXX text escapes are decoded.
• Line endings & padding. Handles LF / CRLF / CR and R12-style space-padded group codes ( 0).
• Ellipse normalisation. DXF requires ratio = minor/major ≤ 1. Files that emit ratio > 1 (a swapped major axis) are normalised to the canonical form — same curve, valid axis — so consumers like OCCT's Geom_Ellipse (which demands majorRadius ≥ minorRadius) get correct geometry. This matches ezdxf's normalisation exactly.
• Binary DXF is detected and rejected (Error.binaryUnsupported) — convert to ASCII DXF first.
• Model space only. Mirrors what ezdxf's modelspace() iterates; BLOCKS definitions are not expanded.

Correctness: tested against an oracle

tools/oracle.py runs ezdxf over the same files and emits per-file entity counts and a geometry digest (the sum of every defining coordinate scalar, in document order). The dxfdump executable emits the identical shape from SwiftDXF:

swift run dxfdump drawing.dxf | python3 -m json.tool

Across an 11-file corpus (~62,000 entities, mixed R12 drawings incl. Jw_cad exports), SwiftDXF matches ezdxf exactly — every entity count and every coordinate scalar, to the bit. The Tests/SwiftDXFTests/CorpusOracleTests.swift suite pins those ezdxf-derived counts as a regression gate (skipped when the corpus is absent; point DXF_CORPUS at a folder of .dxf files to run).

Install

.package(url: "https://github.com/SecondMouseAU/SwiftDXF.git", from: "0.1.0"),
// target dependency: .product(name: "SwiftDXF", package: "SwiftDXF")

Scope

A focused 2D reader, not a full DXF/DWG toolkit. Out of scope for now: DWG, binary DXF, block/insert expansion, splines, hatches, dimensions, and writing. (DXF writing for the JWW format lives in SwiftJWW.)

License

MIT — see LICENSE.