Wednesday, August 15, 2007


Austin and I have this debate over and over when we find a case where third party content doesn't work right with X-Plane (but did in the past due to X-Plane's permissiveness):
  • If we code X-Plane to work around the problem, users get to enjoy the scenery, and authors will never fix the problem.
  • If we code X-Plane to abort, users get grumpy, and authors fix the problem real fast.
What to do? A few versions ago I implemented the scenery warning system (the spanking system) to try to get the best of both worlds. I just discovered another problem that illustrates how this works well.

Before WED some authors made apt.dat 850 layouts by hand using a text editor, and sometimes they forgot to include a closing code on their rings and chains. I can hardly blame them, writing an apt.dat file by hand is very difficult, and I am impressed (and grateful) that they did this.

The apt.dat 850 spec is clear:
  • Pavement chunks (line code 110) must comply with the following:
    • Chunks MUST terminate in a segment point of type 113 or 114.
  • Linear features (line code 120) must comply with the following:
    • Linear features must terminate in a point of type 113, 114, 115 or 116.
    • Linear features do not need to be "closed".
  • Airport boundaries (line code 130) must comply with the following:
    • Boundaries MUST terminate in a segment point of type 113 or 114.
    • Boundaries must be a closed loop and cannot contain holes. As with pavement chunks, the airport boundary cannot overlap itself.

So, you must have one of the closing codes at the end of a boundary, taxiway, or line. But X-Plane 860 doesn't check this and simply assumes a "closed ring" if no code is provided. With X-Plane not telling authors, the authors never caught this mistake.

So now that I know about this (and now that X-Plane needs the end codes to be right, due to other bug fixes) it's time for the spanking system. In future versions of X-Plane:
  • Custom scenery packages with no ending code on a polygon block will automatically be adjusted to be "ring"-type on load-in, for compatibility with X-Plane 860.
  • A detailed message will be printed per polygon in the log.txt file.
  • A single alert box will be shown to the user saying "there is a problem with the custom scenery pack XXX".
The idea is for the dialog box to walk a fine line between being unobtrusive enough for users and annoying enough for authors.

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