In an earlier article, I mentioned that the Autodesk DWF Writer is not for AutoCAD. I developed this article because through my contacts with users in the AutoCAD discussion groups, I encountered customers configuring their page setups to reference the DWF Writer for 2D instead of using the DWF6 ePlot PC3 file. Allow me to make a South Park reference and say:
GDI is Microsoft's Graphics Device Interface. "GDI is bad" is really an overstatement for comedic effect. It works quite well for interfacing with printers. It's just that when it comes to DWF generation, we can do better. This posting is intended to illustrate why - albeit in an overly technically simplified way.
All Autodesk products generate DWF files. Both the Autodesk DWF Viewer and Autodesk Design Review read DWF files. AutoCAD 2007 can read a DWF file as an underlay to a DWG. So we have various products that read and write DWF files. Rather than have each department within the company develop its own code for reading and writing DWF files, we centralize it into one set of code known as the DWF Toolkit. The DWF Toolkit handles both the reading and writing of DWF files. This includes all DWF files - those published by AutoCAD 2007 or even those as far back as AutoCAD R13. We make the DWF Toolkit available publicly on the Autodesk web site.
When an Autodesk design application such as AutoCAD or Inventor interfaces directly with the DWF Toolkit, it has a variety of operations it can perform. It can set colors, draw polylines, draw polygons, draw gradients, etc. Setting attributes and placing geometry in the DWF file accounts for what you see when you view the file; however, in addition to this, the design application can add other information like named views, layers, hyperlinks, or object properties.
This other information, i.e., extra data, is what separates DWF files from traditional plot files.
The Autodesk DWF Writer for 2D acts like a printer. To interface with software applications, it accepts the same standard commands that printers do. Autodesk applications have been specifically developed to interface with the DWF Toolkit. non-Autodesk applications have not. On the other hand, non-Autodesk applications do know how to interface with a printer. Any Windows program knows how to use the standard Windows print mechanism through GDI. The Autodesk DWF Writer for 2D takes advantage of this fact. It acts like a printer, accepts the commands, and instead of putting ink on paper, writes the commands to the DWF file.
Though this approach allows DWF files to be created from applications that have no knowledge of DWF, it does not provide a means of getting the extra data into the DWF file. There are no standard GDI provisions for sending non-drawable items such as hyperlinks or named views to a printer. (Special tricks are available, but both the application and the printer must implement them to make it possible.) Other factors such as gradients or transparency (only available in GDI plus) are not handled optimally as part of DWF publishing via standard GDI. For example, gradients are decomposed into many, many small images. As a result, it is common for a DWF file to be larger when generated from the Autodesk DWF Writer compared to its size when generated from the built-in process of Autodesk design applications. So although the DWF Writer for 2D is valuable in that it allows Autodesk customers to create DWF files from non-Autodesk applications, it is not a substitute for using the built-in DWF publishing capabilities of Autodesk design applications.
The Autodesk DWF Writer for 2D is best used in conjunction with Autodesk software.
- DWF files are generated from Autodesk products using their built-in capabilities.
- DWF files are generated from non-Autodesk applications using the DWF Writer.
- Autodesk Design Review is used to combine the sheets into one DWF file.
This allows a project to share one repository of all of its information in one file - design data and other data. The Autodesk DWF Writer has its rightful place in the world of DWF - it's just better, due to technical limitations of any approach using GDI, to use the built-in publishing capabilities of Autodesk products when possible.
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