Friday, April 03, 2009

XPTools - A Thing of Beauty

I'm going to start blogging about the X-Plane Scenery Tools code tree here...the source code is too technical of a subject for my scenery blog, which is aimed at authors, not programmers. Now that the repository has been cleaned up, other programmers can start working with the code pretty easily...if they Google for answers maybe some of these posts will show up.

Let me show something that I think is really quite beautiful:

That is the root level of the X-Plane Scenery Tools code tree, after a week of Janos and myself bashing at it. A ton of legacy code has been ripped out, file names normalized, library systems standardized across builds, etc. If you want to work with the scenery tools code, you can now do so without going crazy from the mess of random code floating around.

(You will still go crazy trying to understand how the hell the algorithms work. :-)

Here's another thing that I think looks good:

That's the cleaned version of the brains of "MeshTool".  Having it pulled out means that I can now add usability features, like more automated handling of orthophotos quickly and easily.  In fact, so could you!

One more...

Okay - that one doesn't even make sense to me.  The polygon code in the scenery tools had this horrible hack called "dominance" - Andrew can testify to how ugly it was.  The polygon code uses a DCEL as its data structure for polygons.  This means that for every "edge" (line) in the map, there are actually two "half-edges", lines in opposite directions that overlap.

The problem: which one contains the road data?  The old solution was dominance - exactly one was flagged as "dominant" and held the metadata.  The dominance flag helped code figure out where to look/store the data to avoid double-storage.

What a gross hack.  Dominance has been fully removed from the code.  And the data?  It is now possibly stored on either half-edge.  This isn't just a way to remove dominance, it's necessary. A road segment is now stored on the half-edge that goes in the direction of traffic.  So I can now import one-way street grids and the directional information is preserved.

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