[Drawkit] DXF Import Progress / Example

[Allan]

Hello Brad and Graham,

I spent some time looking over your revised SonoPlot application,  
Brad, and realized quickly that the DXF import process is pretty  
complicated due to the way DXF files are formatted. You've certainly  
done a good job with it, but for what I'm doing I need a more  
comprehensive approach to getting all of the object types available in  
the DXF files into my application.

Rather than take on the task of more-or-less writing an entire  
generalized DXF importer based on the SonoPlot approach, I spent some  
time looking for existing DXF import libraries and actually found a  
couple written in c++ that seemed usable. There's a nice summary of  
available tools at http://tomacorp.com/dxf.html where they list and  
compare a number of existing libraries. Here's a quick summary of the  
two I looked at.

(1) DIME (DXF Import Manipulation and Export): (http://www.coin3d.org/lib/dime/ 
) -- looks like this was developed starting about 9 years ago and  
shows some recent activity within the past couple of years.

(2) dxflib (http://www.ribbonsoft.com/dxflib.html) -- a simple  
approach for both reading and writing DXF files. Code is written in c+ 
+ and the concept and approach were quite clear to me. I did not  
explore the writing side of the code as I do not plan to implement  
that at all.

I ended up using (2) dxflib above as the basis for my test project.  
The way this works you create a c++ "creation adapter" class that has  
it's methods called at appropriate points in the DXF reading process.  
For example, when the DXF file reads in a line, it calls the "addLine"  
method and provides the info extracted from the DXF file that is  
needed to create the object. I ended up wrapping this c++ file with my  
own obj-c DXFImporter class. To extend the example, the "addLine"  
method in the c++ class then calles an "addLine" method in my importer  
class and from there I create the DrawKit objects, layers, etc.

So far I have implemented lines, polylines, circles, and arcs. It all  
works pretty well and it shouldn't be that much more work to tackle  
blocks and text as well as any other geometric objects that I decide I  
need.

If you'd like to take a look at what I've done, I posted a zip of my  
Xcode project and associated files, as well as a couple DXF file  
examples at this site.
http://public.me.com/allandaly. I called the project DKSimpleDXF as  
this is just a very basic extension of the simple DK demo that Graham  
created and makes available as part of his downloads. If/when you run  
the project, there is an "Import DXF..." command under the file menu  
that you can use to try out the two sample DXF files I provided. The  
shapes file is simple and small. I created it in AutoCAD 2009 and  
saved it in DXF 2000 format.

The floorplan file is another example that is more like the actual  
types of files I will be using. This has thousands of DXF objects in  
it and works OK. Once imported things are a bit slow to drag and I'm  
starting to get a number of crashes that I'll need to dig into at some  
point, but for now at least it works and I've learned quite a bit  
about the DXF format and the DrawKit logic/implementation. Graham --  
if you happen to try this out I would appreciate it if you have any  
thoughts on the crashes that happen one you try to "select all" and  
"move" the large number of DK objects that I created based on the DXF  
file.

Another question I have for you, Graham, is what is the correct logic  
in the "simple" DK demo program to do a zoom to fit the entire extents  
of the imported DXF into the area of the drawing that you can see on  
the screen? In other words, how would I implement a "zoom extents"  
command now that I have the DXF imported and it extends outside the  
viewable area? I did play with the GCZoom methods some, but couldn't  
make anything work yet -- but I haven't spent much time on that so far.

Any feedback that you have, Brad or Graham, would be helpful and  
appreciated. Thank you.

-Allan

p.s. By the way, Graham, the first very simple extension I did to the  
simple demo program was to create a menu command that programmatically  
creates a rectangle in the drawing. This was just to get my feet wet  
and I started with the logic you wrote in an email string that I found  
in the DK archives. Perhaps it would make sense to include this simple  
menu item call or something similar as an example to new users of how  
the layers, styles, objects, etc all work together.

p.p.s. -- I realize now after writing this that the dxflib is not a  
free open source product, but that the developers are asking for some  
$ for its use. I'm not sure how I'll handle this with my project yet.
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