[Therion] Need help producing scraps.kml without white blobs

[Tarquin Wilton-Jones]

> I have found that stopping the walls on both sides
> of the passage in a single scrap will upset kml generation.

Absolutely. I have reproduced the problem on a small scale like this.

When you have a scrap containing two disconnected sections of "-outline
out", then it gets confused when you use "-outline in" and treats it as
a new "outline out" layered on top, instead of punching out the hole.

[attached outline.png]
[attached whiteblob.jpg]

If you put the disconnected segment of outline into its own scrap, then
the white blob disappears, and you get the correct rendering.

[attached twoscraps.png]
[attached correctrendering.jpg]

This mistake is made a lot of times in the codebase, and seems to be the
main cause of the blobs.

[attached exampleproblem.png]

When rendering the PDFs you also get a tonne of warnings, and these are
trying to help you avoid the problem. The warnings are in the compiler
output, and look like this:

[Warning: scrap outline intersects itself in scrap
WGE17-20 at E5-E23Survey.Wassergang.fulab]

Most of the time, these are an attempt to turn a corner too hard (where
two lines join, try turning the last drag handle towards the next line's
direction), or a Bézier curve point with the drag handles in the wrong
direction, or two walls that overlap very slightly instead of being
joined to the same point. There are quite a few hints randomly scattered
on the Therion wiki about this. It's usually a less important warning
though.

You also get a *really* useful debugging output when generating a .lox
file, where it tells you this exact problem:

C:\Program Files (x86)\Therion\therion.exe: warning --
24B1Scrap at 21NordSurvey.Alter_Teil.fulab -- multiple scrap outer outlines
not supported yet

*This is the cause of your problems.* Fix that, and you fix the white blobs.

I am also seeing "invalid scrap outline" warnings. This usually means
that you have a station without a -name attribute.
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