On 28 Apr 2009, at 02:47, Graham Cox wrote:
Because of the cyclic nature of the network though, there isn't a
way I can see to simply sort the objects into the right order.
I snipped most of the above; anyone who cares to read it should refer
to the original message.
I think the crux of the problem here is that a road can be both child
and parent in the same relationship, or child and grandparent and so
on. This happens because you're allowing arbitrary interconnection,
and the child-parent relationship is important because of the
colouring issue that you mention (i.e. the parent road's colour should
dominate at junctions).
So the question is what to do about all of this.
I *think* the answer might be as follows:
1. Draw *all* the casements (I'm assuming they're the same colour
here; if not, you might need to do step 2 first to break the casements
up as well).
2. For each road, break it into segments such that each segment has no
more than one junction with other roads. So e.g.
(C)
|
(A)==+================(B)
|
(E)====+=====(F)
|
(D)
you would break road CD between the AB-CD junction and the EF-CD
junction.
You might have fun handling more complex junctions...
3. Now each road segment only has one junction, so you can sort the
segments into the correct rendering order using a topographic sort
routine, then simply draw their strokes in that order.
Kind regards,
Alastair.
--
http://alastairs-place.net
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