LibreDWG 0.7

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This manual is for GNU LibreDWG (version 0.7, 2 December 2018).

Copyright © 2010, 2015, 2018 Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation License”.

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1 Overview

LibreDWG is a free C library to read and write DWG files. The DWG file format was created in the 1970s for the then-emerging CAD applications.

This library is part of the GNU project, released under the aegis of GNU. It is made available under GPLv3+, i.e., under the terms of the GNU General Public License version 3, or (at your option) any later version.

It came out of code from the QCad Community Edition product from Ribbonsoft.

1.1 API/ABI version

LibreDWG 0.7 provides the API/ABI version 1. We hope that this doesn't need to change much in the future.

1.2 Coverage

Because the DWG file format is not open, its specification had to be reverse-engineered. The specification is almost complete. The LibreDWG implementation of the specification is an ongoing process; as of version 0.7, coverage is approximately 99%.

It can read the formats R13, R14, R2000, R2004, R2007, R2010, R2013 and R2018 for 99%. R11 and earlier cannot be read yet, only partially. Reading R11 and earlier is only enabled with the development git checkout, not the released tarball.

Here is a list of features that are still missing.

Reading pre-R13 DWG
Reading DWG formats for pre-R13 and some R2010+ non-graphical objects is an ongoing effort, some minor parts are missing. Simple DWG's can be read already, some undocumented classes are skipped.

* ACIS: version 1 is converted to a raw string. ACIS version 2, i.e. the forked variant ACIS 7.0 under the name ShapeManager, is dumped to a string containing the binary SAB format.

Writing pre-R13 and R2004+ DWG
Writing DWG formats for R2004 and later: R2007, R2010, R2013, R2018 is an ongoing effort and not yet implemented. We write as default in the R2000 format.
Reading and writing ASCII and binary DXF
DXF support is an ongoing effort, and about halfway implemented. Ascii DXF's are generated fully, with much more elements and fields and other free libraries, but AutoCAD fails to import some of them. See the TODO file for a detailed coverage report.

Writing binary DXF is still under construction, done about 80%. Reading DXF is not yet fully implemented, this is under construction.

Enabled entities and objects, but unstable, undertested. Field names may change:
For a detailed overview see the files TODO or src/


Unhandled (fields spec'ed but broken/untested):


* PROXY subentities, PROXY_ENTITY




Unhandled (i.e. passed through, no DXF and fields):
no test coverage for entities:
I.e. we need an extended example_2018.dwg with all types, for the following missing entities:


and objects:


1.3 Related projects

Some projects that use DWG (and specifically LibreDWG) are:


Related libraries:

The old version (documented in Esperanto) which was forked to LibreDWG in 2009. But in the meantime it got a DXF reader.
Read the DWG format for all versions r13+ but with much less elements, only those needed for DXF. Written in C++, under the GPLv2 license.
Read the R2000 DWG format. Written in C++, under the GPLv2 license.
The OpenDWG's license does not allow the usage in free software projects.

Compared to libdwg, libdxfrw and libopencad, LibreDWG can read and write much more details. Which is especially important for attached links and data from third party applications: BIM, MAP, GIS, AEC, MECH, ... and for 3D solids and dynamic parametric constraints.

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2 Usage

This chapter describes how to compile and link a program against LibreDWG. To access LibreDWG interface elements (see Types, see Functions), include its header file in the C code.

     #include <dwg.h>

Optionally you can also use the

     #include <dwg_api.h>


Make sure you specify `-lredwg' when linking, such as in this fragment:

     AM_LDFLAGS += -lredwg

Note that the shared object library is named libredwg (with some system-specific extension, e.g., .so), so you do not want to specify -llibredwg, as that would (try to) link against liblibredwg and fail.

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3 Types

LibreDWG types map closely to the type system of the DWG file format. This chapter describes the enums and structs used to define the single DWG structure, which is passed around the functions x(see Functions).

— define: BITCODE_RC char

1 raw signed char

— define: BITCODE_RS short

1 raw unsigned short int

— define: BITCODE_RL long

1 raw unsigned long int

— define: BITCODE_RD double

1 raw IEEE-754 double

— define: BITCODE_B byte

1 bit

— define: BITCODE_BB byte

2 bits

— define: BITCODE_3B byte

1-3 bits

— define: BITCODE_4BITS byte

4 bits (for VIEW view_mode)

— define: BITCODE_BS short

1 bit-encoded unsigned short

— define: BITCODE_BL long

1 bit-encoded unsigned long

— define: BITCODE_BLL uint64_t

1 bit-encoded unsigned 64bit long

— define: BITCODE_BD double

1 bit-encoded double

— define: BITCODE_DD double

1 bit-encoded double with default

— define: BITCODE_MC long int

1-4 modular chars

— define: BITCODE_UMC long unsigned int

1-4 unsigned modular chars

— define: BITCODE_MS long unsigned int

1 modular short, max 2 words

— define: BITCODE_BE double[3]

1 bitencoded extrusion vector

— define: BITCODE_BT double

1 bitencoded thickness value

— define: BITCODE_TV char*

length + ASCIIZ string The default text type until r2004.

— define: BITCODE_TU wchar*

length + windows 2-byte wchar string (UCS-2). The default text type since r2007.

— define: BITCODE_H void*


— define: BITCODE_CMC double[4]

1 encoded Dwg_Color struct

[and some more]

Two types that do not derive from the type system of the DWG file format are the enums for return codes and error codes.

Esp. on 32-bit and windows systems ensure that you define HAVE_STDINT_H and HAVE_INTTYPES_H before including dwg.h to use the proper C99 int32_t,... types, and not just the native fallback types int/long, which are different across platforms. Or include <stdint.h> and <inttypes.h> by your own before dwg.h. With the GNU autotools this usually happens automatically.

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4 Functions

You can use LibreDWG immediately upon loading, without any particular initialization. Only when using some dwg_api functions you might need to initialize the version via dwg_api_init_version(&dwg), when you need other formats than r2000 and you call an API function which does not store the version internally. Most do. This limitation will soon be fixed.

You usually use one set of functions - either decoding or encoding - at a time. All functions use the common data types (see Types). All functions return an error code, and the high-level functions for multiple objects add the error bitmask, which is sorted by severity. When the error exceeds DWG_ERR_CRITICAL, processing is stopped.

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4.1 Decoding

The highest level function for decoding a file is dwg_read_file.

— Function: int dwg_read_file (char *filename, Dwg_Data *dwg)

Open filename and decode it, saving information into dwg. Return 0 if successful.

You can then iterate over the entities in model space or paper space via two ways:

1. by using the dwg.h data structures. Via dwg->object[0], which is of type Dwg_Object_BLOCK_CONTROL, and a custom void process_BLOCK_HEADER(Dwg_Object_Ref* ref):

  Dwg_Object_BLOCK_CONTROL* block_control = dwg->block_control;
  //first all objects in the model space
  //then all objects in the blocks
  for (i=0; i < block_control->num_entries; i++)
  //and last all objects in the paper space

or 2. by using the API functions from dwg_api.h:

  Dwg_Object_BLOCK_CONTROL* block_control = dwg_block_control(dwg);
  for (i=0; i < block_control->num_entries; i++)

and inside the process_BLOCK_HEADER function, you iterate over the objects from the block_header via:

  Dwg_Object* obj = get_first_owned_object(ref->obj);
  while (obj)
      obj = get_next_owned_object(ref->obj, obj);

where process_object checks the type of each object or entity under the Dwg_Object* obj.

For each entity or object type (i.e. a non-graphical dwg object, also tables) there also exist the simple and expensive dwg_get_ENTITY and dwg_get_OBJECT functions:

— Function: int dwg_get_ENTITY (Dwg_Object_Ref *block_header_ref)

Return a malloc'ed NULL-terminated array of all such entities for Model Space, Paper Space or an individual block.

— Function: int dwg_get_OBJECT (Dwg_Data *dwg)

Return a malloc'ed NULL-terminated array of all such DWG objects.

The decoder is driven by the fields definition in the dwg.spec, which adds each field to the object. This is done in the decode.c or decode_r2007.c.

— Function: int dwg_decode_OBJECT (Bit_Chain *dat, Dwg_Object *obj)

Sets the fields for the object from the DWG bitstream.

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4.2 Encoding

Encoding DWG files, i.e. DWG write support, can be disabled via ./configure --disable-write. The default format and only useful one is currently r2000, and needs much work still to be useful enough.

The highest level function for encoding a bitstream to a file is dwg_write_file.

— Function: int dwg_write_file (char *filename, Dwg_Data *dwg)

Open filename and write the dwg to it. Return 0 if successful.

— Function: int dwg_add_object (Dwg_Data *dwg)

Adds a new uninitialized object to the dwg->object[] array. Return 0 or -1 if successful, otherwise DWG_ERR_OUTOFMEM. -1 is the array was re-allocated.

Then for each object or entity type there is a

— Function: int dwg_add_OBJECT (Dwg_Object *obj)

Initializes an object for the given OBJECT or ENTITY type, with all fields being zero'ed. This does not initialize the obj size, type, address, handlestream_size, bitsize fields.

The encoder is driven by the fields definition in the dwg.spec, which adds each field to the object. This is done by encode or any in_* import module.

— Function: int dwg_encode_OBJECT (Bit_Chain *dat, Dwg_Object *obj)

Encodes the DWG bitstream from the fields of the object.

The iterator is similar to above, but you want to encode all data structures, not just the entities. But note that there are currently not enough helper function to create all needed helper sections to store a DWG if you didn't read a DWG into the right a Dwg_Data* dwg struct already. This is especially important when importing from DXF or from an earlier or later DWG version.

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4.3 Other Formats

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4.3.1 DXF

We can write Ascii DXF files in various versions, with much more data than other free DWG libraries, but not as stable as the unfree Teigha library yet. AutoCAD fails to import some of our files still (~20% failure rate).

Options: --minimal (see dwg2dxf or dwgread) creates only a short header with a ACADVER and HANDSEED element, and the entities, without any subclass markers, reactors or handles.

Reading DXF is under construction.

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4.3.2 DXFB

We can almost write Binary DXF files in various versions. Under construction.

Reading DXFB is under construction.

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4.3.3 JSON

We write and read to our own JSON format, which is a readable 1:1 mapping of the DWG structures, and carries much more information than the DXF format.

Writing a JSON to stdout is not recommended, as then ending commas are still there, which is strictly not valid JSON.

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4.3.4 GeoJSON

Work is ongoing to write to the GeoJSON format as specified at See dwgread with the --fmt GeoJSON option.

This is about 70% finished. Check the covered entity types.

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5 Errors

LibreDWG is mostly a library, and as such collects error codes from the highest level function down to the lowest level functions. The error codes are sorted by severity, and only if the error exceeds DWG_ERR_CRITICAL, i.e. DWG_ERR_CLASSESNOTFOUND, processing is stopped.

All error bitmasks are collected during read or write and returned at the end.


Additionally, verbose warning and error messages are printed to stderr.

Unhandled class and Invalid type errors of objects are not severe. A DWG format can store a serialization of many third party classes and objects, and thus we will never be able read all possible types. Unknown types are just stored as binary blob without any DXF codes.

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6 Programs

LibreDWG installs some binary programs to read or write DWG files.

This reads a DWG file, and optionally converts its content to some output formats: JSON, GeoJSON, DXF, DXFB (i.e. Binary DXF).

dwgread [OPTION]... DWGFILE


-v[0-9], –verbose [0-9] verbosity

-O fmt, –format fmt fmt: JSON, DXF, DXFB, GeoJSON

Planned formats: YAML, XML/OGR, GPX, SVG, PS

-o outfile also defines the output fmt. Default: stdout

–help display this help and exit

–version output version information and exit

Currently the options need to be specified in this exact same order.

Create a DWG from a given input file (see DXF, see Binary DXF), optionally via --as-rNNNN as another version. Experimental. For now can only create r2000 DWG files.
Read and write the DWG, optionally via --as-rNNNN as another version, an earlier or later version. The default is writing as r2000.
Prints all layers in a DWG. With -f or --flags also the status of frown, on/off and locked. With --on only the visible layers, which are on and not frozen.
Search regex pattern in all text values in a list of DWGs. The order of options is still important. With -i searches case-insensitive. With -c prints only the count of found texts. With -h or --no-filename does not print the filename. With --type NAME search only NAME entities or objects. With --dxf NUM search only in DXF group NUM fields. With --text searches only TEXT-like entities: TEXT, MTEXT, ATTRIB, ATTDEF.
Convert a DWG to a limited SVG. All paperspace and modelspace enties of type: TEXT, LINE, CIRCLE, ARC, INSERT.
Convert a DWG to a very limited Postscript file. All paperspace and modelspace enties of type LINE.

This requires installation of pslib

Note that the graphical representation for PS and SVG output is severely lacking, block references (insert entities) are not yet exploded, UCS and paper space transformations per entity are not yet done.

Converts DWG files to DXF, optionally via --as-rNNNN as another version, an earlier or later version, or via -m or --minimal as a minimal DXF version, skipping most headers vars, classes, tables and objects.

--binary as a binary DXF file, with full precision, under construction.

The DXF files are created in the current directory and silently overwritten.

Convert a DXF (or Binary DXF) to DWG, optionally via --as-rVER as another version, an earlier or later version. The DXF reader is not yet implemented.

There are also some more examples in the source distribution:

loads a DWG and adds some entities.
converts a DWG to SVG similar to dwg2SVG, but via the dwg_api.h only. The graphical representation for PS and SVG output is severely lacking, block references (insert entities) are not yet exploded , UCS and paper space transformations per entity are not yet done.
lists the not yet reverse-engineered blobs from our example files, and is the framework to guess the field layout for these.

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7 Bindings

LibreDWG generates library bindings to python and perl5 via swig. These can be quite huge, and it is recommended to use ccache. You can easily add bindings to other swig-supported languages, like Go, C#, ruby, php, D, lua, tcl, common lisp, ocaml, or others by yourself. Patches accepted.

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8 Reference API

See the separate refman manual (in pdf or html format, the pdf has ~1800 pages) for a detailed API description, or see the relevant dwg.h, dwg_api.h or the *.spec files.

For reference you might also want to check the public AutoCAD DXF reference manuals, and the ODA OpenDesign_Specification_for_dwg_files.

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9 Reporting bugs

To report bugs or suggest enhancements for GNU LibreDWG, please “submit a bug” at Savannah or send electronic mail to (If you use the web interface, you don't need to also send email, since that is done automatically.) Pull requests at the github mirror at Github are also accepted for now.

For bug reports, please include enough information for the maintainers to reproduce the problem. Generally speaking, that means:

When in doubt whether something is needed or not, include it. It's better to include too much than to leave out something important.

Patches are welcome; if possible, please make them with `git format-patch' and include ChangeLog entries (see Change Log). Please follow the existing GNU coding conventions. See CONTRIBUTING in the source distribution.

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Appendix A GNU Free Documentation License

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    You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.


    A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an “aggregate” if the copyright resulting from the compilation is not used to limit the legal rights of the compilation's users beyond what the individual works permit. When the Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.

    If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document's Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.


    Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.

    If a section in the Document is Entitled “Acknowledgements”, “Dedications”, or “History”, the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.


    You may not copy, modify, sublicense, or distribute the Document except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense, or distribute it is void, and will automatically terminate your rights under this License.

    However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation.

    Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice.

    Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, receipt of a copy of some or all of the same material does not give you any rights to use it.


    The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See

    Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License “or any later version” applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation. If the Document specifies that a proxy can decide which future versions of this License can be used, that proxy's public statement of acceptance of a version permanently authorizes you to choose that version for the Document.


    “Massive Multiauthor Collaboration Site” (or “MMC Site”) means any World Wide Web server that publishes copyrightable works and also provides prominent facilities for anybody to edit those works. A public wiki that anybody can edit is an example of such a server. A “Massive Multiauthor Collaboration” (or “MMC”) contained in the site means any set of copyrightable works thus published on the MMC site.

    “CC-BY-SA” means the Creative Commons Attribution-Share Alike 3.0 license published by Creative Commons Corporation, a not-for-profit corporation with a principal place of business in San Francisco, California, as well as future copyleft versions of that license published by that same organization.

    “Incorporate” means to publish or republish a Document, in whole or in part, as part of another Document.

    An MMC is “eligible for relicensing” if it is licensed under this License, and if all works that were first published under this License somewhere other than this MMC, and subsequently incorporated in whole or in part into the MMC, (1) had no cover texts or invariant sections, and (2) were thus incorporated prior to November 1, 2008.

    The operator of an MMC Site may republish an MMC contained in the site under CC-BY-SA on the same site at any time before August 1, 2009, provided the MMC is eligible for relicensing.

ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:

       Copyright (C)  year  your name.
       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.3
       or any later version published by the Free Software Foundation;
       with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
       Texts.  A copy of the license is included in the section entitled ``GNU
       Free Documentation License''.

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with...Texts.” line with this:

         with the Invariant Sections being list their titles, with
         the Front-Cover Texts being list, and with the Back-Cover Texts
         being list.

If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.

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