Re: [igraph] Plotting graph on cairo surface in Python

[Stephen J. Gaffigan]

Tamas,

Thanks for the quick reply. This worked perfectly.

Steve

On Mon, Jun 18, 2012 at 11:25 AM, Tamás Nepusz <address@hidden> wrote:
> Hi Stephen,
>
> The first catch is that igraph.plot() _constructs_ the plot itself (i.e. it 
> returns a Plot instance) but it does not draw it yet on the surface you 
> specified. This is probably an oversight on my side because igraph.plot() 
> would draw the graph if the target you specify is a string (i.e. a filename) 
> or None (meaning to plot the graph into a temporary file and show that). The 
> workaround for the time being is to do this:
>
> plot = igraph.plot(g, surface, bbox=(width, height), layout=layout)
> plot.redraw()
>
> The next thing you should do is to ensure that the plot igraph will draw also 
> has a transparent background (it is white by default):
>
> plot = igraph.plot(g, surface, bbox=(width, height), layout=layout)
>
> plot.background = None
> plot.redraw()
>
> This should do the trick. As igraph 0.6 has just been released, I cannot fix 
> the bug with igraph.plot in the 0.6 branch, but I will make sure that 0.7 
> does not have this bug.
>
> Best,
> Tamas
>
>> I'm using the Python igraph bindings and would like to plot my graph
>> with a transparent background. I think I need to use
>> igraph.Graph.plot's support for a Cairo surface target. Can anyone
>> point me at an example of plotting a graph to a cairo surface, or else
>> is there a better way to do this? The below code snippet shows the
>> approach I'm trying to get to work. The output image is transparent,
>> but there's no graph.
>>
>> Thanks for the library. I've gotten a lot of miles out of it on a wide
>> variety of network analysis and visualization projects.
>>
>> Steve
>>
>> import igraph,cairo
>> g = igraph.Graph([(0,1), (0,2), (2,3), (3,4), (4,2), (2,5), (5,0),
>> (6,3), (5,6)])
>> layout = g.layout('kk')
>> width,height = 900,600
>> surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, width, height)
>> ctx = cairo.Context(surface)
>> ctx.scale(width,height)
>> ctx.rectangle(0, 0, 1, 1)
>> ctx.set_source_rgba(0,0,0,0)
>> ctx.fill()
>> igraph.plot(g,surface,bbox=(width,height),layout=layout)
>> surface.write_to_png('example.png')
>>
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>
>
>
>
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