cadcraft/docs/file-format-parity.md

# File-format parity

> **Last reviewed:** 2026-10-10 · **Last updated:** 2026-10-11 · **Change:** minor (DXF/DWG saved at a chosen version 2000–2018, binary DXF written, #421) · **Target:** Autodesk AutoCAD 2027

Every format AutoCAD 2027 reads or writes, with CADCraft's support, fidelity and tests. Work
items are in [gaps.md](gaps.md#file-formats); the weighted score feeds
[target-app-parity.md](target-app-parity.md).

**Headline (estimated):** file formats ≈ **30%** of AutoCAD's. Opening the commonest 2D DXF/DWG
drawings works, but saving is lossy: everything CADCraft doesn't model is dropped, and no test
uses a real third-party file. DXF and DWG save at 2000–2018 (2018 by default, #421). Remaining: **≈ 170–280 Opus 5.5 hours**:
≈ 40–60 h for DXF/DWG fidelity (the part that decides beta), ≈ 110–180 h for the other formats
below, and ≈ 20–40 h for 3D exchange formats that wait for 3D modelling.

## How this was measured

- CADCraft: read from `crates/dxf`, `crates/io` (`dxf_read.rs`, `dxf_write.rs`, `pdf.rs`,
  `svg.rs`, `tests.rs`) and `crates/dwg` on 2026-10-10. Nothing was run (the measurement pass
  did no builds).
- AutoCAD: the formats in its Open/Save As/Import/Export/Attach/Plot dialogs, from Autodesk's
  published documentation and the menu tree in `xtask/data/menu-catalog.txt`. The installed
  AutoCAD 2027 for Mac bundle was inspected by listing names only (clean-room rule: nothing
  inside it is read): `Resources/Support` lists `acad.lin`, `acadiso.lin`, `acad.pat`,
  `acadiso.pat`, `acad.mln`, `.dct` spell dictionaries, `.pss` and `.shx` files, which confirms the
  supporting formats below exist in the target. None of them may be copied.
- No AutoCAD-produced file is committed or used as a fixture. A real-file corpus needs owner
  action (see [gaps.md](gaps.md)): files made by people who license them to us, kept in a
  separate `storytold/cadcraft-corpus` repo.

## DWG, version by version

AutoCAD 2027 opens every DWG version from R2.0 onward and saves 2018 (AC1032, still the current
DWG format), 2013, 2010, 2007, 2004, 2000 and R14. CADCraft reads DWG by converting it to DXF
with the `acadrust` 0.6.3 crate and reading that DXF; it saves by writing its own R2000 DXF and
converting it to a DWG of the chosen version (#421): SAVEAS `version`, else the drawing's own
version (the file's `$ACADVER`, 2018 for a new drawing), at least 2004 unless 2000 is asked for.
The bridge repairs two acadrust 0.6.3 gaps in 2010+ DWG: merged table cells and table-style
title/header suppression.

| DWG version | Code | AutoCAD 2027 | CADCraft read | CADCraft write | Tested how |
|---|---|---|---|---|---|
| R1.0–R2.6, R9, R10, R11/R12 | MC0.0–AC1009 | read | **no** (`is_dwg` accepts only `AC10xx` magic; acadrust doesn't target pre-R13) | no | — |
| R13 | AC1012 | read | acadrust claims support; untested | no | none |
| R14 | AC1014 | read, write | acadrust claims support; untested | **no** | none |
| 2000–2002 | AC1015 | read, write | yes via bridge | yes, when asked for (no true colours, transparency or table styles: the format has none) | synthetic round trips (`dwg_at_every_version_reads_back`, `dwg_roundtrip_keeps_non_ascii_text`) |
| 2004–2006 | AC1018 | read, write | via bridge | yes | `dwg_at_every_version_reads_back`, `dwg_roundtrip_keeps_extension_data` |
| 2007–2009 | AC1021 | read, write | via bridge | yes | `dwg_at_every_version_reads_back` |
| 2010–2012 | AC1024 | read, write | via bridge | yes | `dwg_at_every_version_reads_back`, `ac1024_dwg_with_many_entities_opens` |
| 2013–2017 | AC1027 | read, write | via bridge | yes | `dwg_at_every_version_reads_back` |
| 2018–2027 | AC1032 | read, write (default) | via bridge; untested on real files | yes (default for new drawings) | `dwg_at_every_version_reads_back` (synthetic only) |
| Web build | — | — | **no** (error: "save as DXF") | no | — |

Everything lost in the DXF read/write paths below is also lost through DWG, plus whatever
`acadrust`'s own DXF output omits (proxy objects, ACIS data, custom objects: not measured). User
report #57: a 10 MB DWG failed after about two minutes; limits now stop runaway conversions
early (#175), but the throughput problem remains. **DWG ≈ 30% read, ≈ 15% write.**

## DXF, version by version

| DXF version | AutoCAD 2027 | CADCraft read | CADCraft write |
|---|---|---|---|
| R12 (AC1009), ASCII | read, write | yes: no version gating; old-style POLYLINE/VERTEX read (polyface meshes flattened to 3D polylines) | **no** |
| R12 binary | read, write | **no** (binary parser expects R13+ 2-byte group codes) | no |
| R13–R2018, ASCII | read, write each of 2000/2004/2007/2010/2013/2018 | yes, one reader for all versions | yes, each of 2000–2018 (#421): R2000 structure (later versions add only optional groups) with that `$ACADVER`; UTF-8 text from 2007; no CLASS instance counts (91) |
| R13–R2018, binary | read, write | yes | yes, each of 2000–2018 (SAVEAS `binary`; a binary file stays binary on QSAVE) |
| Code pages (`$DWGCODEPAGE`, ANSI_932/936/949/950/125x) | yes | **no**: UTF-8, else Latin-1, so pre-2007 CJK and Cyrillic files are garbled | writes `\U+` escapes (#169), which is correct |
| `\U+`/`\M+` escapes | yes | `\U+` yes; `\M+` not checked | `\U+` yes |

### DXF content: read and write by object type

| Content | Read | Write | Notes |
|---|---|---|---|
| LINE, POINT, CIRCLE, ARC, ELLIPSE, LWPOLYLINE (widths, bulges, elevation), SPLINE, RAY, XLINE | yes | yes | round-trip tests |
| POLYLINE 2D/3D | yes | yes (as LWPOLYLINE / 3D POLYLINE) | polyface and polygon meshes flattened: lossy |
| TEXT, MTEXT, ATTDEF, INSERT + ATTRIB | yes | yes | ATTDEF prompt kept (#137) |
| DIMENSION (all 7 kinds) | yes | yes, with anonymous `*D` blocks | a reopened dimension's `*D` block is regenerated under its name, unreferenced ones dropped (#495); DIMASSOC objects written |
| LEADER | yes | yes | |
| MULTILEADER | **no** (becomes Unknown) | **no**: our MLeaders are written as LEADER + MTEXT | MULTILEADER is AutoCAD's default leader since 2008 |
| HATCH pattern / solid | yes | yes | |
| HATCH gradient | yes | yes (#162, fixes #80) | |
| SOLID, TRACE, 3DFACE | yes | yes | |
| ACAD_TABLE | yes | yes (entity + block) | |
| VIEWPORT | yes | yes; frozen-layer lists kept (#150) | VP layer colour overrides lost (#99, PR #197) |
| IMAGE | partial (no IMAGEDEF, so the file path is empty) | **dropped** | |
| WIPEOUT | yes | yes (#147, fixes #79) | |
| MLINE, REGION, 3DSOLID, BODY, SURFACE, MESH, TOLERANCE, SHAPE, HELIX, UNDERLAY, OLE2FRAME, LIGHT, CAMERA, SECTION, POINTCLOUD, proxy entities | kept as Unknown (raw tags) | written back as read, with their CLASS records (#528); **dropped by DWG save** (acadrust) | only their layer follows edits |
| Header variables | all read | 36 written | AutoCAD writes about 280 |
| Tables: LAYER (+ transparency, description), LTYPE, STYLE, DIMSTYLE, BLOCK_RECORD | yes | yes | |
| Tables: VPORT, VIEW, UCS, APPID | **not read** | VPORT one record; VIEW and UCS empty; APPID yes | named views and UCSs lost |
| Objects: LAYOUT, DICTIONARY, XRECORD, TABLESTYLE, DIMASSOC | yes | yes | |
| Objects: GROUP, MLINESTYLE, MLEADERSTYLE, IMAGEDEF, SCALE, VISUALSTYLE, PLOTSETTINGS, materials, field objects | ignored | not written (ACAD_GROUP empty) | groups lost |
| Foreign xdata, extension dictionaries, reactors | **not kept** | — | third-party application data lost |
| Handles and owners | entity handles kept; others regenerated | consistent | stable across CADCraft re-saves (#495); other programs' table and object handles renumbered once |

**DXF ≈ 50% read, ≈ 30% write** (estimated; weights: common 2D entities 50%, annotation objects
20%, tables/objects 15%, foreign data preservation 15%).

## Other formats

| Format | AutoCAD 2027 | CADCraft | Hours to parity (est.) |
|---|---|---|---|
| DWT templates | open, save | no (no template support) | 3–5 |
| DWS standards | open, save, CHECKSTANDARDS | no | 6–10 |
| PDF output (PLOT, EXPORTPDF) | multi-sheet, layers, searchable text, hyperlinks | vector PDF 1.4, one page, lineweights; **no font objects** (text is strokes), no layers (OCG), no multi-sheet | 10–15 |
| PDF import (PDFIMPORT) and PDF underlays (PDFATTACH) | yes | no | 15–25 |
| Raster images attach (PNG, JPEG, TIFF, BMP …) | yes | IMAGE entity exists, no attach/loading/display path | 6–10 |
| PNG / JPEG / BMP / TIFF export | PNGOUT, JPGOUT, BMPOUT, TIFOUT | PNG; SVG too (AutoCAD doesn't export SVG) | 1–2 |
| DWF/DWFx export, DWF underlay | yes | no | 10–15 |
| DGN import/export/underlay | yes | no (needs a public spec; owner decision) | 25–40 |
| WMF, EPS, ACIS SAT, STL, FBX, IGES/STEP (Windows), 3DS | various | no; most are 3D and wait for M11 | 20–40 |
| SHX fonts (`.shx`, big fonts) | read | **not parsed**: our stroke font or FONTALT stands in, so text metrics differ from AutoCAD | 8–12 |
| Linetype (`.lin`) and hatch pattern (`.pat`) files | load user files | own built-in library only; user files can't be loaded | 3–5 |
| Plot styles (`.ctb`, `.stb`), plotter configs (`.pc3`), `.pmp` | yes | plot style tables in our own JSON format ([plot-styles.md](plot-styles.md)) and kept in the drawing; binary `.ctb`/`.stb` not read (no public spec); no `.pc3`/`.pmp` | 6–10 |
| Scripts (`.scr`) | SCRIPT | script text through the CLI, MCP and control channel; no SCRIPT command reading a `.scr` file | 1–2 |
| Aliases (`.pgp`), CUI(x), workspaces | yes | no | 6–10 |
| AutoLISP (`.lsp`, `.fas`, `.vlx`), `.dll`/`.arx` plug-ins | yes | no | see [gaps.md](gaps.md) (M12) |
| Data extraction (`.csv`, `.xls`) and data links | yes | no | 6–10 |
| eTransmit (`.zip` packages) | yes | no | 4–6 |

## Tests

`crates/io/src/tests.rs` has 36 tests (round trips of entities, styles, associativity, tables,
constraints, non-ASCII text, DWG round trips, hostile input). **All inputs are synthetic**:
inline strings or our own writer's output. No test opens a file made by another program, and no
external validator runs in CI (ezdxf's audit was run by hand once, 2026-10-06). The next step is
a licensed real-file corpus with an open → save → re-open → compare test per file, and checking
our output in AutoCAD black-box.

## Revision history

| Date | Change | Summary |
|---|---|---|
| 2026-10-11 | minor | DXF (ASCII and binary) and DWG saved at 2000–2018, 2018 by default (#421) |
| 2026-10-10 | minor | WIPEOUT and gradients written since #147/#162; other save losses remain (#201, #204, #208, #209, #213, #223) |
| 2026-10-10 | major | First file-format parity doc: DWG and DXF version by version, per-object read/write, other formats |