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List:       graphviz-devel
Subject:    [graphviz-devel] Re: Modifying an edge in a non-strict graph [PATCH]
From:       Shaun Jackman <sjackman () bcgsc ! ca>
Date:       2008-12-18 0:32:56
Message-ID: 49499A38.8050905 () bcgsc ! ca
[Download RAW message or body]

Found the bug. A patch follows.

Cheers,
Shaun

2008-12-17  Shaun Jackman  <sjackman@gmail.com>

	* cmd/gvpr/compile.c (getval) <F_isedge>: The graph argument of
	isEdge should be NULL not curgraph.

--- cmd/gvpr/compile.c.orig	2008-12-17 16:27:54.000000000 -0800
+++ cmd/gvpr/compile.c	2008-12-17 16:28:05.053274000 -0800
@@ -799,7 +799,7 @@
  		error(ERROR_WARNING, "NULL head node passed to isEdge()");
  		v.integer = 0;
  	    } else
-		v.integer = PTR2INT(isEdge(state->curgraph, np, hp, key));
+		v.integer = PTR2INT(isEdge(NULL, np, hp, key));
  	    break;
  	case F_isedgesg:
  #ifdef USE_CGRAPH

Shaun Jackman wrote:
> Okay, I found the solution is to use isEdge. Unfortunately, there's a 
> regression from 2.18 to 2.20.3. In 2.20.3, isEdge does not return the 
> existing edge as expected. See the test case below.
> 
> Cheers,
> Shaun
> 
> $ cat weight
> BEG_G { graph_t g = graph ("merge", "U"); }
> E {
>         node_t t = clone(g, tail);
>         node_t h = clone(g, head);
>         edge_t e = isEdge(t, h, "");
>         if (e == NULL)
>                 e = edge(t, h, "");
>         e.weight = e.weight + 1;
> }
> END_G { $O = g; }
> $ gvpr-2.18 -f weight <<<'graph g {a--a;a--b;a--b;}'
> graph merge {
>         a -- a   [weight=1];
>         a -- b   [weight=2];
> }
> $ gvpr-2.20.3 -f weight <<<'graph g {a--a;a--b;a--b;}'
> graph merge {
>         a -- a   [weight=1];
>         a -- b   [weight=1];
>         a -- b   [weight=1];
> }
> 
> Shaun Jackman wrote:
>> Hi,
>>
>> The following example from the gvpr man page `Produces  a  strict 
>> version  of  the  input  graph,  where the weight attribute of an edge 
>> indicates how many edges from the input graph the edge represents.'
>>
>>               BEG_G { graph_t g = graph ("merge", "S"); }
>>               E {
>>                 node_t h = clone(g,$.head);
>>                 node_t t = clone(g,$.tail);
>>                 edge_t e = edge(t,h,"");
>>                 e.weight = e.weight + 1;
>>               }
>>               END_G { $O = g; }
>>
>> Unfortunately, because the graph is strict it also removes loops. In 
>> fact, it dies if the input graph contains a loop. If I simply make the 
>> output graph non-strict by removing the "S" option to graph(), it no 
>> longer works as desired:
>>
>> $ gvpr -f weight <<<'graph g {a--a; a--b; a--b;}'
>> digraph merge {
>>         a -> a   [weight=1];
>>         a -> b   [weight=1];
>>         a -> b   [weight=1];
>> }
>>
>> edge() doesn't return the existing edge as the man page says it does. 
>> I presume this behaviour only applies to strict graphs. So, how can I 
>> fetch the existing edge rather than creating a new edge in a strict 
>> graph?
>>
>> Cheers,
>> Shaun
> 
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