Edge widths with a colorlist are not 50:50

1

Hello…
Long time user of pygraphviz. I’m drawing directed edges between two nodes with a two color color list like dir=both, color=‘orange:black’. This displays a line with arrowheads on both ends. Perfect. It seems like one of the colors is about 90%+ of with width of the edge itself. In this example I added the penwidth=10 parameter to make the edge fat and you can see that the line is mostly black with only a thin stripe of orange.

image

I tried changing the colorlist to add fractions like this: color=‘orange;0.90:black’ but it didn’t see to do much

How do I get a roughly 50/50 thickness of the two colors?

I’m using prog=‘neato’ and format=‘svg’ in case that matters. I think pygraphviz is 1.5.

Thanks in advance!

Ed

2

Can you produce a “dot” output & share it?

3

Hi Steve,

Thanks for your reply… Never looked at it in dot before but here is the edge in question. I assume you didn’t want then entire graph since it’s pretty large:

“switchS2B510x7c0187fc1/22” [height=0.5,
label=“0x7c0187+ 2 others”,
len=2.0,
pos=“1316.1,1125.4”,
shape=oval,
style=dashed,
width=2.4444];
switchS2B – “switchS2B510x7c0187fc1/22” [key=“switchS2B%fc1/22%switchS2B510x7c0187fc1/22”,
arrowsize=1.5,
color=“#ffa500:#000000”,
dir=both,
label=“fc1/22 (32G)”,
len=2.5,
lp=“1266,1015.3”,
penwidth=10,
pos=“s,1290.8,906.7 e,1314,1107.2 1293.4,928.87 1299.1,978.58 1306.6,1043.5 1311.4,1084.9”];

I just set the colors with color=“#ffa500:#000000”, The black part of the edge is much thicker than the orange part. The black and orange arrowheads look fine though.

Thanks for your help.

Ed

4

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5

Hi Steve,

OK I guess. Are you asking me to do something?

Thanks,

Ed

6

colorlist is poorly documented and works non-intuitively for edges.

  • each color in a list defines 1 “unit” (my term) of linear color (point/width). If the penwidth value is greater than the number of colors (true in your example), then the last color is used for the rest of the penwidth. Restated in English: your penwidth is 10, so 1/10 of the width is given to the 1st color and 9/10 is given to the 2nd color. What you seem to want is
    color="#ffa500:#ffa500:#ffa500:#ffa500:#ffa500:#000000"
  • the fraction option in a colorlist defines a fraction of the length, not the width! This allows changing colors along the length of an edge. Handy, but not what you are trying to do today.

Whew! I learned something new today.

7

Hi Steve,

OK thanks a bunch! That’s a bit difficult to deal with I guess from a programming perspective. But I guess it is what it is. I did notice the percentages dealt with the length of the edges and not the width but I guess I was hoping there was some syntax to give me 50:50 fairly easily. I vary with penwidth on certain edges so I will have to include some logic to repeat the colors as well (or at least the initial color).

Thanks!! Much much appreciated!

Ed

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