Make link editor background transparent

[Alizter]

It would be nice if we could configure the link editor to have a transparent background. That would allow people to put the editor over a picture and trace a knot. Alternatively, being able to import pictures would be nice too.

[culler]

That seems like a good idea to me. I think a transparent background for a Tk Canvas might be challenging, but I will look into it. Allowing a background image, say from a pdf file, should be relatively easy, however.

[NathanDunfield]

@Alizter: You might be interested in KnotFolio can take an image of a knot (including from a photo) and convert into a diagram that SnapPy will accept. I haven't used it enough to know how complicated an diagram it can handle.

@culler: I agree this would be a nice addition. I think Tk can only display gif and pmg/ppm files on its own, for png and jpeg one needs to use PIL as well to display them. Converting from pdf to a bitmapped format probably requires outside converters (e.g. imagemagick).

[culler]

@NathanDunfield You are right, of course. Pdf would be problematic. The most likely format would probably be jpeg, since people will probably take a picture of the knot with their phone. But then we would have to deal with new iphones, which will produce HEIC images. Those are a real pain. But Pillow can deal with them if you add a special plugin.

[Alizter]

@Alizter: You might be interested in KnotFolio can take an image of a knot (including from a photo) and convert into a diagram that SnapPy will accept. I haven't used it enough to know how complicated an diagram it can handle.

Thanks. This is not quite as sophisticated as I had hoped however. But I suppose its good if you have a pen drawing of a knot.