Dxf Reference How To Write The

See the Access section for information regarding importing DWG files.

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Points are converted from Global Coordinates to screen coordinates in function GetPoint().

The most popular CAD formats are AutoCAD DWG and AutoCAD DXF, the latter being simplified dwg - a special format to be used by developers.

The problem is that DXF and DWG formats are really complicated.

They have dozens of objects with hundreds of interaction tricks and thousands of properties.

Official DXF Reference from Autodesk has 256 pages though it fails to describe many important facts.

Hence, the development for CAD drawings is often required but is not easy to implement.

Dxf Reference How To Write The

This article is to tell you how to write the DXF reader in C, what problems can arise and of course you can find example in C source code, which is free for use under MPL license.

The value after 20 is Y1, after 30 - Z1 (0 in 2D drawings).

X2, Y2, Z2.

So here we see the line with coordinates (39.19., 36, 45.

We need to load the file to stream and to take lines - even lines (0, 2, 4.) are CODE, odd lines (1, 3, 5.) are VALUE and repeat this procedure step by step till the end of file EOF.

For instance, many Entities have base point - in DXF, which is described by codes: 10 (x), 20 (y), 30(z).

So we can make Object-Oriented structure to read and to store the properties in order to avoid double-coding.

We will store Layer and Base Point in entity DXFVisibleEntity which will be ancestor for all visible entities.

The dash lines stand for associations between DXF file objects and objects, programmed in C.

Class DXFVisibleEntity is the ancestor for all visible Entities.

There is a special entity Block which may have many inserts in the CAD drawing.

Block is just set of entities (including nested blocks) which can be inserted many times.

So if you want to know the color of entity, it is not enough to read.

Entity.Color - it is necessary to see all the Inserts and Blocks.

Pay attention that the most common color is ByLayer and in order to read the correct color, we need to read the color from Layer entity.

It has many tricks, for instance checking the layer.name 0 - in DXF layer 0 is special and elements with color ByLayer get the color from Block if they are on 0 layer.

This is how it works: There is a class DXFGroup which is an ancestor of Entity and which can store array of Entities.

For instance, Block is ancestor of DXFGroup and can store many entities like LINE.

For better unification, we can use ONE BASE GROUP ENTITY object for all the drawing, this Entity will have array of all entities, each of them can also be the Group - the classic Tree.

Dxf Reference Manual