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IDProjectCategoryView StatusDate SubmittedLast Update
0001852graphvizDotpublic2010-04-06 03:562011-10-19 16:50
ReporterChris Korda 
Assigned Togviz 
PlatformOSx86-Windows-XPOS Version
Summary0001852: edge misses top of node with invtriangle shape

If the inverted triangle node shape (invtriangle) is used,
and connections are made to the flat top of the triangle via
the northern ports, the resulting edges miss the flat top of the
triangle by a significant amount. The result suggests that in
this case the edge-positioning code ignores the invtriangle
attribute and substitutes a default shape (ellipse?).
dot command:
  dot -Tjpg -omytest.jpg mytest.txt
Additional Information
This problem is related to the port code. See modified example:
\<A HREF="b1921.gv"\>input\</A\> and \<A HREF="b1921.png"\>output\</A\>.

Thanks for the report. I've applied a fix for this particular case which should be in tomorrow's snapshot.

We still need more cleanup of compassPort placement code. I think e,w ports on assymetric shapes will still fail at the moment.

Thanks for the update. I enclose another related but distinct case which
might be interesting. It also uses invtriangle but with all three north
ports connected. In this case NW and NE intersect the top of the node, but N
does not. Note that this example fails with other node shapes besides
invtriangle, e.g. try it with house or invhouse.

I can submit this via the bug reports form if you prefer.

I'm curious about the nature of the problem. Do shapes have some data that
defines where their ports are? And if so, do the inverted shapes have their
own data, or are they handled by flipping the ports around the origin?

In other words, would it be helpful to try all the nodes shapes against
these two cases of mine? I will volunteer to do this if it's helpful.

The problem was affecting N,S,E,W but not NE,NW, SE,SW which were
slightly better coded.

The problem only affects asymmetric shapes: N,S, if the shape is
asymmetric vertically, and E,W if the shape is asymmetric horizontally

I've put in a partial fix for N,S, but haven't fixed E,W yet. The code
really needs to be recoded
to accept a port at any angle; instead of the case statement in which
the same code is repeated multiple times, or not if it didn't seem too
important ;-)

If you're interested, the code that needs rewriting is in
lib/common/shapes.c in the compassPort()
function. I think a better coding would be to convert the compass
request to an angle,
find the intersection of that angle from the node center to the node
bounding box, then use the edge clipping code to work back to the
intersecion with the polygon. Basically we shouldn't be using a case
statement at all.

The fix I've applied works for your other example. See attached.
You can see my fix so far with:
      cvs diff -u -r1.140 -r1.141 lib/common/shapes.c

The fix I've applied works for your other example. See attached.

Thanks, and yes it sounds convoluted and in need of a rewrite. It does tend
to happen in older systems, I deal with it all the time. Regarding "code ...
repeated multiple times", at my work we call these "paste bombs", because
they're made with the paste key, and they cause big problems later when some
of them get modified but others not.

I do have one question though. Is there an easier way to do what I'm trying
to do? All I want is to ensure that for each node, its inputs (edge heads)
connect on the top, and its outputs (edge tails) connect on the bottom.
Maybe there's already some dot feature I missed that adds this constraint?
Compass ports are overly constraining: I don't want to have specify
east/west, dot should keep that degree of freedom. Also compass ports won't
work if there are more than three edges connecting to the node top or

If there's no such feature, perhaps I should propose it? The syntax is easy,
an edge could specify an orientation (TBLR) instead of a compass point, e.g.


or in a LR graph,


I'm unclear as to what is being proposed. Is edge1 the name of a node, and B is short-hand for sw/s/se, whatever works?
Or is this a new keyword, and edge1:B specifies the previous constraint for all out-edges?

The original grammar did contain a specification for the angle an edge entered a node but, as with ports, it was never
implemented. Presumably one might also want a fuzzy angle.

If the code can be simplified, great, but using ports affects mincross, positioning and edge routing, and everything has
to work correctly under the transformations used for rankdir.

My interpretation would be "foonode:T -> ..." means any that an outedge of foonode is constained to originate at any convenient angle from ne to nw. Convenient to the edge layouter."

Or, perhaps alternatively, that the edge induces a virtual port anywhere arout the node periphery between ne and nw.
> The original grammar did contain a specification for the angle an edge entered a node but, as with ports, it was never
> implemented. Presumably one might also want a fuzzy angle.

Yes, I think we are talking about fuzzy angles, or floating ports, with contrained flexibility left to the edge layouter.


  foo:B -> bar:T

means that particular edge from foo to bar goes from the bottom of foo to the top of bar?

Note that we do have the port _ tells the router to use some reasonable port exposed to the outside of the node, so we already
have a notion of fuzziness.

The nice thing about having non-fuzzy ports is that this aids crossing reduction.

Yes, exactly. For example in this case:
alpha:B -> foo:T
bravo:B -> foo:T
charlie:B -> foo:T
delta:B -> foo:T

all four edges would emanate from the bottom of their respective nodes, and
would terminate at the top of node foo. Ideally the edge heads would be
spaced evenly along the top of foo, and would appear in the same order that
they would have appeared if 'B' had not been specified.

L and R would exhibit the same behavior but horizontally, which would be
especially useful in a LR graph.

The fuzziness has advantages: the user avoids having to explicitly order the
edges, avoids special cases for different numbers of edges, and isn't
limited to three edges.
TagsNo tags attached.
VERSION     2.24
Attached Files

- Relationships

-  Notes
User avatar (0000093)
erg (administrator)
2011-10-19 16:50

The code has been fixed to handle :e and :w on asymmetric node shapes.

The request to support :T, :B, :R, :L modifiers is still open.

- Issue History
Date Modified Username Field Change
2011-04-28 04:03 user1 New Issue
2011-04-28 04:03 user1 Assigned To => user1
2011-10-19 16:50 erg Note Added: 0000093
2011-10-19 16:50 erg Severity cosmetic => feature
2011-10-19 16:50 erg Description Updated View Revisions
2011-10-19 16:50 erg Additional Information Updated View Revisions

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