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A brief information about ObjectARX…

14 Comments Feb-01-2008 | Posted by M. Mazhar Basa | Printable Version | Level |

Autocad Programming

Hello everbody,

Today, I will give brief information about ObjectARX, which is one of the innovative steps in history of AutoCAD. It is another way for programming in AutoCAD, just like AutoLISP and VBA. Main difference of it is the programming languages it uses, which is C++ in versions up to AutoCAD 2007® and C++.NET starting with this version.

However, as it uses C++ language and it requires knowledge of the programming structure of AutoCAD, DLL (dynamically linked library) etc. it took interest of mainly software developers who develop AutoCAD integrated software products, that are customized in special subjects (i.e. plug-ins, add-ons, modules that are used to aid specific kinds of drawings like reinforced concrete, steel detailing drawings, architectural drawings etc.).

Compared to other two customization tools AutoLISP and VBA, ObjectARX is the most complicated one. For example, if you are about to write a code to draw one simple line you can do it in AutoLISP and VBA with only a few lines, besides you can do this inside AutoCAD through the relevant editor. But if you do it with ObjectARX, you will have to prepare a new project in a C++ compiler like Visual Studio, and create up 1-5 (changing from the experience of programmer) code files that needs be compiled together with the AutoCAD libraries the and write up to 100 lines of code. This may sound annoying or just crazy. But the point is, due to the fact that your ObjectARX application is using some part of the original AutoCAD source with ObjectARX, you can control a huge part of run-time environment of AutoCAD. You can manipulate/change the reactions of AutoCAD to specific actions, you can add new reactions that AutoCAD does when predefined conditions occur, you can add temporary graphics, drawing aids, dynamic objects, user interfaces, database connections, communication with other software/hardware etc.. you can even change whatever you don’t like in AutoCAD’s operation sequence or logic ; shortly whatever you can program in C++, whatever you can imagine.

What you create with ObjectARX is a DLL file, which can be loaded into AutoCAD, similar to loading AutoLISP or VBA applications. It is not different from any other DLL that AutoCAD uses. This is achieved by using some part of the AutoCAD source code. When AutoDESK introduced ObjectARX concept, what they did is simply to open some of their source code (which is indeed a very precious commercial secret) so that third party software developers could use this source code to develop their own applications that works as a part of AutoCAD. This enabled developers to use AutoCAD only for the user interface of their own program or they simply created some specific tools that work as a part of AutoCAD, help those who already use AutoCAD to prepare their drawings. Main idea is that you can apply the “object-oriented programming” with C++. This means that you can use AutoCAD’s basic objects to create your own objects. When you are making a drawing what you are doing is simply to put together the basic drawing objects like lines, texts, points etc. together in a systematic and oriented manner . For example you are creating a signboard by putting together a line object as post a text object as something written on it, and a circle, suppose that it is a circular sign board. If you look into any drawing prepared with AutoCAD or any CAD tool, you can such objects prepared in the same manner. What if you could have directly created a signboard object. Up to this point, idea is same as writing a macro, or creating a block, or an attribute. However idea of creating “custom objects” with ObjectARX is far beyond these. While creating a block, you are limited to what AutoDESK has programmed for BLOCK objects, but with ObjectARX you can take the already existing Block object that AutoDESK has programmed inside AutoCAD and add properties or modify existing properties. You can append your own objects, algorithms, combine different objects together and add dynamic properties to the object that is affected by the things that change when you are drawing etc.

Here I could only give only a brief information about ObjectARX and what you can do with it. However, due to the wide range of possibilities and control it gives to the programmer, its capacity are limited to the capacity of the ObjectARX programmer . In my next article, I will explain the components required for creating an ObjectARX application (C compiler and AutoCAD libraries). Please stay tuned:)