libdxfrw - Technical Specifications

Project Overview

Project Name: libdxfrw Version: 0.6.3 License: GNU General Public License v2 (or later) Original Author: José F. Soriano (Rallaz) Maintainers: codelibs, Nicu Tofan, Miguel E. Hernández Cuervo

Purpose

libdxfrw is a free C++ library for reading and writing DXF (Drawing eXchange Format) files in both ASCII and binary formats. It also supports reading DWG (AutoCAD drawing) files from versions R14 through V2015.

Main Features

DXF File Read/Write
- Read and write DXF files in ASCII format
- Read and write DXF files in binary format
- Support for multiple DXF versions: R12, 2000, 2004, 2007, 2010
DWG File Reading
- Supported versions: R14 to V2015
- Version-specific reader implementations:
  - dwgReader15: R14 version
  - dwgReader18: R2004 version
  - dwgReader21: R2007 version
  - dwgReader24: R2010 version
  - dwgReader27: R2013/R2015 versions
Supported CAD Drawing Entities
- Basic shapes: Points, Lines, Rays, XLines
- Curves: Circles, Arcs, Ellipses, Splines
- Polylines: 2D/3D Lightweight Polylines
- 3D shapes: 3D Faces, Traces, Solids
- Text: Single-line text, Multi-line text
- Annotations: Hatches, Dimensions, Leaders
- Others: Block references, Images, Viewports
Supported CAD Objects
- Layers
- Line Types
- Text Styles
- Dimension Styles
- Viewports
- Application IDs
- Block Definitions

Architecture

Core Class Structure

dxfRW (Main API Class)
├── DRW_Interface (Abstract Interface)
├── dxfReader/dxfWriter (DXF I/O Handlers)
├── dwgReader (DWG Reader Base)
│   ├── dwgReader15 (R14)
│   ├── dwgReader18 (R2004)
│   ├── dwgReader21 (R2007)
│   ├── dwgReader24 (R2010)
│   └── dwgReader27 (R2013-2015)
├── DRW_Header (Header Variables)
├── DRW_Entity (Geometric Entities)
│   ├── DRW_Point
│   ├── DRW_Line
│   ├── DRW_Arc
│   ├── DRW_Circle
│   ├── DRW_Ellipse
│   ├── DRW_LWPolyline
│   ├── DRW_Polyline
│   ├── DRW_Spline
│   ├── DRW_Text
│   ├── DRW_MText
│   ├── DRW_Hatch
│   ├── DRW_Dimension (various dimension types)
│   └── Other entities
└── DRW_Object (Non-geometric Objects)
    ├── DRW_Layer
    ├── DRW_LType
    ├── DRW_Textstyle
    ├── DRW_Dimstyle
    └── Other objects

Directory Structure

libdxfrw/
├── src/                      # Library source code
│   ├── libdxfrw.h/cpp       # Main API class
│   ├── drw_interface.h      # Abstract interface
│   ├── drw_entities.h/cpp   # Entity definitions
│   ├── drw_objects.h/cpp    # Object definitions
│   ├── drw_header.h/cpp     # Header variables
│   ├── drw_base.h           # Basic data structures
│   └── intern/              # Internal implementation
│       ├── dxfreader.h/cpp     # DXF reader
│       ├── dxfwriter.h/cpp     # DXF writer
│       ├── dwgreader*.h/cpp    # DWG readers
│       ├── dwgbuffer.h/cpp     # DWG buffer
│       ├── drw_textcodec.h/cpp # Character encoding
│       └── Other utilities
├── dwg2dxf/                  # DWG to DXF converter tool
├── dwg2text/                 # DWG to text extractor tool
├── bin/                      # Executable scripts
└── vs2013/                   # Visual Studio 2013 project

API Specifications

Main Class: dxfRW

Constructor

dxfRW(const char* name);

Parameters: name - File name to process
Description: Creates an instance for processing DXF/DWG files

Main Methods

Reading

bool read(DRW_Interface *interface_, bool ext);

Parameters:
- interface_: Callback interface implementation
- ext: Apply extrusion to convert to 2D
Returns: true on success, false on failure
Description: Reads the file and calls interface methods for each entity

Writing

bool write(DRW_Interface *interface_, DRW::Version ver, bool bin);

Parameters:
- interface_: Interface implementation providing data
- ver: DXF version (R12, 2000, 2004, 2007, 2010)
- bin: Output in binary format
Returns: true on success, false on failure

Entity Writing Methods

bool writePoint(DRW_Point *ent);
bool writeLine(DRW_Line *ent);
bool writeCircle(DRW_Circle *ent);
bool writeArc(DRW_Arc *ent);
bool writeEllipse(DRW_Ellipse *ent);
bool writeLWPolyline(DRW_LWPolyline *ent);
bool writeSpline(DRW_Spline *ent);
bool writeText(DRW_Text *ent);
bool writeMText(DRW_MText *ent);
bool writeHatch(DRW_Hatch *ent);
// ... many more

Table Object Writing Methods

bool writeLayer(DRW_Layer *ent);
bool writeLineType(DRW_LType *ent);
bool writeTextstyle(DRW_Textstyle *ent);
bool writeDimstyle(DRW_Dimstyle *ent);
bool writeVport(DRW_Vport *ent);
bool writeAppId(DRW_AppId *ent);

Interface: DRW_Interface

Applications must inherit from this interface and implement callback methods.

Required Methods

Header

virtual void addHeader(const DRW_Header* data) = 0;

Table Objects

virtual void addLayer(const DRW_Layer& data) = 0;
virtual void addLType(const DRW_LType& data) = 0;
virtual void addDimStyle(const DRW_Dimstyle& data) = 0;
virtual void addTextStyle(const DRW_Textstyle& data) = 0;
virtual void addVport(const DRW_Vport& data) = 0;
virtual void addAppId(const DRW_AppId& data) = 0;

Blocks

virtual void addBlock(const DRW_Block& data) = 0;
virtual void setBlock(const int handle) = 0;
virtual void endBlock() = 0;

Entities

virtual void addPoint(const DRW_Point& data) = 0;
virtual void addLine(const DRW_Line& data) = 0;
virtual void addRay(const DRW_Ray& data) = 0;
virtual void addXline(const DRW_Xline& data) = 0;
virtual void addCircle(const DRW_Circle& data) = 0;
virtual void addArc(const DRW_Arc& data) = 0;
virtual void addEllipse(const DRW_Ellipse& data) = 0;
virtual void addLWPolyline(const DRW_LWPolyline& data) = 0;
virtual void addPolyline(const DRW_Polyline& data) = 0;
virtual void addSpline(const DRW_Spline* data) = 0;
virtual void addInsert(const DRW_Insert& data) = 0;
virtual void addTrace(const DRW_Trace& data) = 0;
virtual void add3dFace(const DRW_3Dface& data) = 0;
virtual void addSolid(const DRW_Solid& data) = 0;
virtual void addMText(const DRW_MText& data) = 0;
virtual void addText(const DRW_Text& data) = 0;
virtual void addHatch(const DRW_Hatch *data) = 0;
virtual void addViewport(const DRW_Viewport& data) = 0;
virtual void addImage(const DRW_Image *data) = 0;

Dimensions

virtual void addDimAlign(const DRW_DimAligned *data) = 0;
virtual void addDimLinear(const DRW_DimLinear *data) = 0;
virtual void addDimRadial(const DRW_DimRadial *data) = 0;
virtual void addDimDiametric(const DRW_DimDiametric *data) = 0;
virtual void addDimAngular(const DRW_DimAngular *data) = 0;
virtual void addDimAngular3P(const DRW_DimAngular3p *data) = 0;
virtual void addDimOrdinate(const DRW_DimOrdinate *data) = 0;

Others

virtual void addLeader(const DRW_Leader *data) = 0;
virtual void linkImage(const DRW_ImageDef *data) = 0;
virtual void addComment(const char* comment) = 0;

Writing Methods

virtual void writeHeader(DRW_Header& data) = 0;
virtual void writeBlocks() = 0;
virtual void writeBlockRecords() = 0;
virtual void writeEntities() = 0;
virtual void writeLTypes() = 0;
virtual void writeLayers() = 0;
virtual void writeTextstyles() = 0;
virtual void writeVports() = 0;
virtual void writeDimstyles() = 0;
virtual void writeAppId() = 0;

Build Systems

1. Autotools (Recommended)

autoreconf -vfi
./configure
make
sudo make install

Configuration Files

configure.ac: Autoconf configuration
Makefile.am: Automake templates
Library version: 0.6.3 (CURRENT=6, REVISION=3, AGE=0)

Dependencies

Required: libiconv (character conversion)
Standard Library: stdlib.h, string.h
Math Functions: sqrt()

2. CMake

mkdir build
cd build
cmake .. -DCMAKE_BUILD_TYPE=Release
cmake --build . --config Release
sudo cmake --build . --config Release --target install

Key CMake Settings

Minimum CMake version: 3.10
Build target: Static library dxfrw
Installation paths:
- Headers: include/
- Library: lib/ (Linux/macOS), Debug/lib/ or Release/lib/ (Windows)

3. Visual Studio 2013

Solution file: vs2013/libdxfrw.sln
Project file: vs2013/libdxfrw.vcxproj
NuGet package: libiconv 1.14.0.11

4. Docker

# Build image
docker build --rm -t codelibs/libdxfrw .

# Build library
docker run -t --rm -v `pwd`:/work codelibs/libdxfrw:latest /work/build.sh

Base image: CentOS 7
Output: dxfrw.tar.gz (install location: /opt)

Utility Tools

1. dwg2dxf

Command-line tool to convert DWG files to DXF format.

dwg2dxf [options] input.dwg [output.dxf]

Files:

dwg2dxf/main.cpp: Entry point
dwg2dxf/dx_iface.h/cpp: Interface implementation
dwg2dxf/dwg2dxf.1: Man page

2. dwg2text

Tool to extract text information from DWG files.

dwg2text input.dwg

Files:

dwg2text/main.cpp: Entry point
dwg2text/dx_iface.h/cpp: Interface implementation
dwg2text/dwg2text.1: Man page

3. dxf2txt.py

Python script to dump DXF files in text format.

python bin/dxf2txt.py input.dxf

Data Structures

Basic Types

namespace DRW {
    enum Version {
        UNKNOWNV,    // Unknown
        R12,         // R12 DXF
        R14,         // R14 DXF
        R2000,       // R2000 DXF
        R2004,       // R2004 DXF
        R2007,       // R2007 DXF
        R2010,       // R2010 DXF
        R2013,       // R2013 DXF
        R2015        // R2015 DXF
    };
}

Entity Base Class

class DRW_Entity {
public:
    enum DRW_EntityType {
        POINT, LINE, CIRCLE, ARC, ELLIPSE,
        LWPOLYLINE, POLYLINE, SPLINE,
        INSERT, TEXT, MTEXT, HATCH,
        DIMENSION, LEADER, VIEWPORT, IMAGE,
        // ... others
    };

    DRW_Coord basePoint;      // Base point
    std::string layer;        // Layer name
    std::string lineType;     // Line type
    int color;                // Color number
    double thickness;         // Thickness
    double ltypeScale;        // Line type scale
    int handle;               // Handle
    // ... other properties
};

Coordinate Type

class DRW_Coord {
public:
    double x;
    double y;
    double z;
};

Character Encoding Support

libdxfrw supports multiple character code pages:

CP932: Japanese (Shift-JIS)
CP936: Simplified Chinese (GB2312)
CP949: Korean
CP950: Traditional Chinese (Big5)

Implementation Files

src/intern/drw_textcodec.h/cpp: Character encoding conversion engine
src/intern/drw_cptable932.h: Japanese code page
src/intern/drw_cptable936.h: Simplified Chinese
src/intern/drw_cptable949.h: Korean
src/intern/drw_cptable950.h: Traditional Chinese
src/intern/drw_cptables.h: Code page table integration

Error Handling and Debugging

Debug Level Settings

void setDebug(DRW::DBG_LEVEL lvl);

Debug Levels:

DRW::NONE: No debug output
DRW::DEBUG: Debug information output

Debug Utilities

src/intern/drw_dbg.h/cpp: Debug output utilities

Performance Considerations

Buffering

dwgBuffer: Efficient binary data processing when reading DWG files
Supports bit-level read operations

Memory Management

Entities and objects are passed by pointer or reference
Memory management is handled by the interface implementation side

Ellipse to Polyline Conversion

void setEllipseParts(int parts);

Set the number of segments when converting ellipses to polylines. Increasing the number of segments improves accuracy.

Test Data

External test data repository:

fess-testdata/autocad

Contains sample files of various DXF/DWG file versions, useful for integration testing.

Known Limitations

DWG File Writing Not Supported: Only DWG file reading is supported
Limited Entity Support: May not support all entities from the latest AutoCAD versions
Reed-Solomon Decoding: Error correction functionality for DWG files is limited

Version History

See the ChangeLog file for details.

Major development milestones:

2011: Project started
2013: Added DWG R2004 support
2014: Added DWG R2010/R2013 support
2015: Added DWG R2015 support
2020s: Ongoing community maintenance

License

GNU General Public License v2.0 (or later)

See the COPYING file for details.

Contributors

José F. Soriano (Rallaz): Original author
Nicu Tofan: Contributor
Miguel E. Hernández Cuervo: Contributor
codelibs: Maintainer

References

Official website: http://sourceforge.net/projects/libdxfrw
GitHub: https://github.com/codelibs/libdxfrw
DXF Reference: AutoCAD DXF Specification (Autodesk official documentation)

Support and Community

Report issues and submit pull requests through the GitHub repository: https://github.com/codelibs/libdxfrw/issues

Last Updated: 2025-11-08

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