Re: [graphviz-interest] Straight line drawn as a curve (Petersen.gv)

On 08/21/2013 11:20 AM, Emden R. Gansner wrote:
> On 8/21/13 5:49 AM, Ryan Schmidt wrote:
>> Why has Graphviz drawn this line as three connected Bezier curves? 
>> The X-coordinate of each point is identical; it seems that this could 
>> just as easily have been a straight line from 17,647.95 directly to 
>> 17,108.05.
> Short answer: it is an overlooked optimization.
>
> After placing the nodes on discrete ranks, dot adds dummy nodes to 
> each long edge so that all edges join adjacent ranks. This graph is 
> used for reducing
> crossings and node positioning. During edge routing, dot constructs a 
> collection of boxes in which the edge is routed to avoid nodes, other 
> edges, etc. It
> also recognizes stretches where it can just use a straight line 
> segment. For the edge 0 -- 5, the edge is constructed by creating a 
> Bezier through some boxes
> at the beginning, followed by a vertical line (represented as a 
> degenerate Bezier), and ending with another Bezier through some boxes 
> at the end. In this case,
> it just happens to occur that the first and last Beziers are also 
> vertical line segments collinear with the middle segment. This would 
> be fairly rare, so there is
> no check for it, and no attempt to simplify the final output.
>
>     Emden
Also, note that (AFAIK) we don't have a way to syntactically distinguish 
between 2pt lines and 4pt beziers in the "pos" attribute syntax.




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