Issue 60 in diagrams: Tools for more accurate boundary calculations in common cases
diag...@googlecode.com
Owner: ----
Labels: Type-Enhancement Priority-Medium Component-Lib
New issue 60 by byor...@gmail.com: Tools for more accurate boundary
calculations in common cases
http://code.google.com/p/diagrams/issues/detail?id=60
(09:46) < Taejo> are the bounds functions for polygons exact?
(09:47) < byorgey> Taejo: they are exactly what they are defined to be =)
(09:47) < byorgey> Taejo: the bounding function tells you how far you
have to go to reach a line which completely encloses the polygon
(09:48) < byorgey> Taejo: so placing two things next to each other means
there will be a perpendicular line with one on one side and one on the other
(09:48) < Taejo> byorgey, but they are approximations, in general?
(09:48) < byorgey> Taejo: no
(09:49) < fryguybob> For anything convex the union of bounds calls on
all "angles" would be the exact complement of the shape.
(09:49) < byorgey> Taejo: they are exact. Sorry, I wasn't sure what you
were asking at first.
(09:50) < Taejo> no problem. let me upload a picture to show what's
going on
(09:50) < Taejo> http://i.imgur.com/EtmX8.png
(09:51) < byorgey> Taejo: ah, yeah, I see what's going on
(09:51) < byorgey> Taejo: it follows from what I said if you think about
it carefully
(09:52) < Taejo> ah, you're right
(09:52) < Taejo> I see now
(09:52) < byorgey> if you ask for the "boundary" of a polygon in a
direction not perpendicular to one of its edges...
(09:52) < byorgey> it is a bit annoying though. I'm trying to think of
the best way to do what you want to do.
(09:53) < byorgey> Taejo: well, one easy solution would be to draw the
lines between the *centers* of the polygons
(09:53) < byorgey> and just draw the polygons on top of them
(09:54) < Taejo> byorgey, yeah, that works... until I add arrowheads :(
(09:54) < byorgey> ah, hmm
(09:54) < Taejo> I think in that case I'll just have to live with the
gaps
(09:56) < fryguybob> I think we could make an approximate solution that
gave any desired accuracy.
(09:56) < byorgey> yeah, I've thought about things like that before
(09:57) < fryguybob> Not for bounds in general, but for this specific kind
of case.
(09:57) < byorgey> you can automatically vary the angle at which you
query the bounding function to try to find a local minimum
(09:57) < byorgey> we could also put in a special case for polygons which
would work exactly
(09:57) < fryguybob> true
(09:58) < byorgey> well, for arbitrary paths really
(09:58) < Taejo> byorgey, I'm working on a library to draw graphs with
arbitrary diagrams as nodes
(09:58) < byorgey> Taejo: cool!
(09:58) < Taejo> I could have a special case for when the nodes are
described by a path
(10:00) < byorgey> Taejo: I don't think this is something your graph
library ought to have special cases for
(10:00) < byorgey> we ought to put tools in the diagrams standard library
to help deal with such situations
(10:01) < byorgey> hmm, rather than special-casing the bounding function
code, we could have something which extends a path right up to a diagram
(10:01) < byorgey> since we do have more exact coverage information from
the query
(10:02) < byorgey> you could specify an extension length which is long
enough and then it would do a binary search
(10:02) < fryguybob> Something like binary search between the center and
the bounds?
(10:02) < byorgey> exactly
(10:02) < byorgey> oh! even better.
(10:03) < fryguybob> I think that will only work if you are convex.
(10:03) < byorgey> true
(10:03) < byorgey> I actually meant a binary search between the end of
the path and some specified distance beyond it
(10:04) < fryguybob> Yeah, holes are a problem
(10:04) < byorgey> but exact boundary points for convex shapes via binary
search would be good too
(10:04) < fryguybob> Most of the time it would probably work well though.
(10:05) < byorgey> yup
Stephen Tetley
the connector points of "blob" diagrams.
Wumpus has supported anchors for quite a while now, but both the
interface and implementation are a bit crummy.
diag...@googlecode.com
Comment #1 on issue 60 by byor...@gmail.com: Tools for more accurate
http://code.google.com/p/diagrams/issues/detail?id=60
We have an even better idea now: along with the current bounding function,
track a function of type
Point -> Vector -> Scalar
which tells you the distance from the given point to the *furthest* point
contained in the diagram along the given vector. Making the point an
argument is required so that these can be translated properly.
Such a function would not be useful for putting diagrams next to each other
but IS useful for finding points on the actual boundary of a diagram.
This function would also be added to the information you get in a
LocatedBounds object (when using withName etc.)
Functions like 'boundary' etc. should use this new feature. 'align', '(|||
)', etc. should remain as they are.
diag...@googlecode.com
Comment #2 on issue 60 by Max.Rab...@gmail.com: Tools for more accurate
http://code.google.com/p/diagrams/issues/detail?id=60
In later discussion, we came up with another way which doesn't need
root-finding. Alongside the dividing hyperplanes function, track the
boundary (convex hull). Representing this as a function giving the distance
from the local origin to the boundary in a given direction is not
compositional, but it looks like the representation which gives the
distance from any given point in a given direction *is*.