CadLib for creating DXF(Drawing Interchange Format) files

Introduction

What is DXF?

Drawing Interchange Format (DXF) files enable the interchange of drawings between AutoCAD and other programs. DXF files can be either ASCII or binary formats. Because ASCII DXF files are more common than the binary format, CadLib uses ASCII DXF format.

What is CadLib?

The CadLib is not a Computer Aided Design (CAD) program. It is a tool for creating DXF files that are used in the CAD programs. It consists of two parts. One of them is a Dynamic Link Library to create the DXF file. The other part is the programming interface. It is a class that integrates the cadio.dll functions. It can be used in Microsoft Visual C++ projects. In addition, the cadio.dll can be used in other Win32 programs.

Why use CadLib?

In some programs, it is needed to create a drawing output for use in other programs such as AutoCad. For example, in a "Building Detail Sheet Generator Program", the program needs to create a drawing output. And the most standard format for communicating drawing data is DXF.

DXF file structure

The DXF format is a tagged data representation of all the information contained in a drawing file. Tagged data means that each data element in the file is preceded by an integer number that is called a group code. A group code's value indicates what type of data element follows. This value also indicates the meaning of a data element for a given object (or record) type. Virtually all user-specified information in a drawing file can be represented in DXF format. (from AutoCad's DXF reference)

A DXF file consists of some sections. Each section has some drawing data in itself. The CadLib uses the following sections:

HEADER
TABLES
BLOCKS
ENTITIES

The main reference for DXF file structure that is used for CadLib is the AutoCad's DXF reference. You can find more information about DXF file structure here.

Classes

The classes are interfaces between CadIO.dll and the main program. "Test" has come with CadLib to demonstrate how to generate a DXF file with CDxfFileWrite and CDrawing classes.

CDxfFileWrite class

CDxfFileWrite gathers all the commands needed to directly create a DXF file. Usage of CDxfFileWrite is as follows:

Create the DXF file

CDxfFileWrite dxffile;
dxffile.Create( "d:\\test.dxf" );

Begin and end the HEADER section. It's here for compatibility with some CAD programs. Others work without having HEADER section.

// Header Section ------------------------------------------
dxffile.BeginSection(SEC_HEADER);
dxffile.EndSection();
// close HEADER section ------------------------------------

Begin the TABLES section and put the LAYER, LTYPE, STYLE, DIMSTYLE table-types as many as you want and then close the section

// Tables Section ------------------------------------------
dxffile.BeginSection(SEC_TABLES);

// LTYPE table type -------------------------
dxffile.BeginTableType(TAB_LTYPE);

DXFLTYPE ltype;
double elem[4];

// Continuous
ZeroMemory(<ype, sizeof(ltype));
ltype.Name = "Continuous";
ltype.DescriptiveText = "Solid line";
dxffile.AddLinetype(<ype);

// DASHDOT2
ZeroMemory(<ype, sizeof(ltype));
ltype.Name = "DASHDOT2";
ltype.DescriptiveText = "Dash dot (.5x) _._._._._._._._._._._._._._._.";
ltype.ElementsNumber = 4;
ltype.TotalPatternLength = 0.5;
ltype.Elements = elem;
elem[0] = 0.25;
elem[1] = -0.125;
elem[2] = 0.0;
elem[3] = -0.125;
dxffile.AddLinetype(<ype);

dxffile.EndTableType();
// close LTYPE table type -------------------

// LAYER table type -------------------------
result &= dxffile.BeginTableType(TAB_LAYER);
result &= dxffile.AddLayer("Layer1", 1, "Continuous");
result &= dxffile.AddLayer("Layer2", 2, "Continuous");
result &= dxffile.AddLayer("Layer3", 3, "Continuous");
result &= dxffile.AddLayer("Layer4", 4, "Continuous");
result &= dxffile.EndTableType();
// close LAYER table type -------------------

// STYLE table type -------------------------
dxffile.BeginTableType(TAB_STYLE);

DXFSTYLE tstyle;
ZeroMemory(&tstyle, sizeof(tstyle));
tstyle.Name = "Style1";
tstyle.PrimaryFontFilename = "TIMES.TTF";
tstyle.Height = 0.3;
tstyle.WidthFactor = 1;
dxffile.AddTextStyle(&tstyle);

dxffile.EndTableType();
// close STYLE table type -------------------

// DIMSTYLE table type ----------------------
dxffile.BeginTableType(TAB_DIMSTYLE);

DXFDIMSTYLE dimstyle;

// DIM1
ZeroMemory(&dimstyle, sizeof(dimstyle));
dimstyle.Name = "DIM1"; // DimStyle Name
dimstyle.DIMCLRD = 2; // Dimension line & Arrow heads color
dimstyle.DIMDLE = 0.0000; // Dimension line size after Extensionline
dimstyle.DIMCLRE = 2; // Extension line color
dimstyle.DIMEXE = 0.1800; // Extension line size after Dimline
dimstyle.DIMEXO = 0.0625; // Offset from origin
dimstyle.DIMBLK1 = "ClosedFilled";// 1st Arrow head
dimstyle.DIMBLK2 = "ClosedFilled";// 2nd Arrow head
dimstyle.DIMASZ = 0.1800; // Arrow size
dimstyle.DIMTXSTY = "Style1"; // Text style
dimstyle.DIMCLRT = 3; // Text color
dimstyle.DIMTXT = 0.1800; // Text height
dimstyle.DIMTAD = 1; // Vertical Text Placement
dimstyle.DIMGAP = 0.0900; // Offset from dimension line
dxffile.AddDimStyle(&dimstyle);

dxffile.EndTableType();
// close DIMSTYLE table type ----------------

dxffile.EndSection();
// close TABLES section ------------------------------------

Begin ENTITIES section and put entities data (LINE, CIRCLE, SOLID, TEXT, ARC, POINT, DIMLINEAR) and finally close the section

// Entities Section ------------------------------------------
dxffile.BeginSection(SEC_ENTITIES);

// set current layer to Layer2
dxffile.SetCurrentLayer("Layer2");
// draw a line
dxffile.Line(1.2, 3.3, 7.5, 7.7);
// draw a circle
dxffile.Circle(7.8, 4.3, 1.75);
// set current layer to Layer4
dxffile.SetCurrentLayer("Layer4");

// draw a solid
REALPOINT points[4];
points[0].x = 10.4; points[0].y = 7.2;
points[1].x = 13.6; points[1].y = 7.4;
points[2].x = 13.1; points[2].y = 4.9;
points[3].x = 10.9; points[3].y = 5.9;
Solid(4, points);

// set current textstyle to Style1
dxffile.SetCurrentTextStyle("Style1");
// draw text
dxffile.Text("Sample Text", 5.9, 6.7, 0.3, 35);
// draw a dimension line
dxffile.SetCurrentDimStyle("DIM1");
dxffile.DimLinear(6.05, 3, 9.55, 3, 9.55, 2, 0, "3.50");

dxffile.EndSection();
// close ENTITIES section ----------------------------------

Close the DXF file
```
dxffile.Close();
```

CDrawing class

CDrawing class has all the commands to create a drawing in memory and save it as a DXF file. Usage of CDrawing is as follows:

Create the on-memory drawing
```
CDrawing drw;
drw.Create( );
```

Create new LAYER, LTYPE, STYLE, DIMSTYLE table-types as many as you want.

// Tables Section ------------------------------------------
// LTYPE table type -------------------------
LTYPE ltype;
OBJHANDLE objhandle1;

// Continuous
ZeroMemory(<ype, sizeof(ltype));
strcpy(ltype.Name, "Continuous");
strcpy(ltype.DescriptiveText, "Solid line");
objhandle1 = drw.AddLinetype(<ype);

// DASHDOT2
ZeroMemory(<ype, sizeof(ltype));
strcpy(ltype.Name, "DASHDOT2");
strcpy(ltype.DescriptiveText, 
  "Dash dot (.5x) _._._._._._._._._._._._._._._.");
ltype.ElementsNumber = 4;
ltype.PatternLength = 0.5;
ltype.Elements[0] = 0.25;
ltype.Elements[1] = -0.125;
ltype.Elements[2] = 0.0;
ltype.Elements[3] = -0.125;
drw.AddLinetype(<ype);

// LAYER table type -------------------------
LAYER layer;

// Layer1
ZeroMemory(&layer, sizeof(layer));
strcpy(layer.Name, "Layer1");
layer.Color = 1;
layer.LineTypeObjhandle = objhandle1; // Continuous
drw.AddLayer(&layer);

// Layer2
ZeroMemory(&layer, sizeof(layer));
strcpy(layer.Name, "Layer2");
layer.Color = 2;
layer.LineTypeObjhandle = objhandle1; // Continuous
drw.AddLayer(&layer);

// STYLE table type -------------------------
STYLE style;

ZeroMemory(&style, sizeof(style));
strcpy(style.Name, "Style1");
strcpy(style.PrimaryFontFilename, "TIMES.TTF");
style.LastHeightUsed = 0.3;
style.WidthFactor = 1;
objhandle1 = drw.AddTextStyle(&style);

// DIMSTYLE table type ----------------------
    DIMSTYLE dimstyle;

// DIM1
ZeroMemory(&dimstyle, sizeof(dimstyle));
strcpy(dimstyle.Name, "DIM1"); // DimStyle Name
dimstyle.dimclrd = 2; // Dimension line & Arrow heads color
dimstyle.dimdle = 0.0000; // Dimension line size after Extensionline
dimstyle.dimclre = 2; // Extension line color
dimstyle.dimexe = 0.1800; // Extension line size after Dimline
dimstyle.dimexo = 0.0625; // Offset from origin
strcpy(dimstyle.dimblk1, "ClosedFilled");// 1st Arrow head
strcpy(dimstyle.dimblk2, "ClosedFilled");// 2nd Arrow head
dimstyle.dimasz = 0.1800; // Arrow size
dimstyle.dimtxstyObjhandle = objhandle1;// Text style
dimstyle.dimclrt = 3; // Text color
dimstyle.dimtxt = 0.1800; // Text height
dimstyle.dimtad = 1; // Vertical Text Placement
dimstyle.dimgap = 0.0900; // Offset from dimension line
drw.AddDimStyle(&dimstyle);

Make entities data (LINE, CIRCLE, SOLID, TEXT, ARC, POINT, DIMLINEAR, POLYLINE).

// Entities Section ------------------------------------------
// set current layer to Layer2
drw.SetLayer("Layer2");
// draw a line
drw.Line(1.2, 3.3, 7.5, 7.7);
// draw a circle
drw.Circle(7.8, 4.3, 1.75);
// set current layer to Layer1
drw.SetLayer("Layer1");

// draw a solid
REALPOINT points[4];
points[0].x = 10.4; points[0].y = 7.2;
points[1].x = 13.6; points[1].y = 7.4;
points[2].x = 13.1; points[2].y = 4.9;
points[3].x = 10.9; points[3].y = 5.9;
drw.Solid(points[0], points[1], points[2], points[3]);

// set current textstyle to Style1
drw.SetTextStyle("Style1");
// draw text
drw.Text("Sample Text", 5.9, 6.7, 0.3, 35);
// draw a dimension line
drw.SetDimStyle("DIM1");
drw.DimLinear(6.05, 3, 9.55, 3, 9.55, 2, 0, "3.50");

Save data to a DXF file.
```
drw.SaveDXFFile(DxfFileName);
```
Destroy CDrawing and free allocated memory.
```
drw.Destroy();
```

Loading data from a DXF file

Create the on-memory drawing.
```
CDrawing drw;
drw.Create( );
```
Use LoadDXFFile member function to load DXF file into memory.
```
drw.LoadDXFFile("Sample.dxf");
```

That's all!

Conclusion

Since I am a Civil Engineer, I decided to write a program to generate a beam or columns detail sheet without the use of AutoCAD. I have written a program that, with a little data about beam or column, will create the detail sheet automatically. Output of this program is a DXF file and it can be shown in AutoCAD or it can be plotted with it. This program can save the time for drawing the detail sheet with AutoCAD. If you are an AutoCAD operator, you will understand the meaning of words that are used in this article, or if you are a programmer who wants to write a program to create DXF files, first you need a little knowledge about AutoCAD or the drawing programs such as is mentioned above. This code can be useful for programmers who need to create DXF files from their programs. CadLib is not the best one and also there are many commercial software for creating DXF files but they are not open source. Feel free to change the code. Your comments in regards to this article will cause the improvement of CadLib.

History

20 Dec 2002
- First release of CadLib
19 Jan 2003
- Some bug fixes
- Added Dimension-Line support. It's a combination of other entity commands like "Line" and "Solid"
- Added BLOCKS section support
- Added Arc, Point and InsertBlock commands for ENTITIES section
- Text command has been improved
11 May 2003
- Added CDrawing class to store drawing data in memory and change the data before saving it as a DXF file.
28 June 2003
- Added DXF read capability to CDrawing class
- Some bug fixes of CDrawing class when writing data to a DXF file
22 Nov 2003 (CadLib Version 2.00)
- Added Drawing View capability
- Added PolyLine command (by Tran duy Dung)
- Improved DXF loading speed
- Some bug fixes of drawing memory management functions
24 Aug 2004 (CadLib Version 2.10)
- Added ZoomExtents Function
- Improved Viewing functions to show Dashed Lines
- Added "ChangeEntity" & "DeleteEntity" commands
- Added Dimension view capability
- Fixed a bug occures when viewing a rotated block
- Improved viewing of texts