Adjust text anchor of labels

[donkirkby]

We've run into problems with short tracks near the left or right edges. If the label is longer than the track rectangle, then the label text can flow past the edge of the diagram.

Here's an example, including our current workaround:

from genetracks import Figure, Track, Multitrack

f = Figure()

f.add(Track(1, 1500, label='Track with a long contig'))

# The problem
f.add(Track(1, 150, label='Track with a long name'))

# A workaround
f.add(Multitrack([Track(1, 150),
                  Track(1,
                        1500,
                        label='Short track with centred name',
                        color='none')]))

f.show(w=900).saveSvg("alignment.svg")

Here's how it looks:

I thought it might be helpful to set the text-anchor attribute of the labels. I don't think there's a good way to estimate the width of the text, so the best I could think of was to use start when the track starts on the left third of the diagram, middle when it starts in the middle third, and end when it starts on the right third.

If you think that's a reasonable approach, I can prepare a pull request.

[jeff-k]

Thank you very much for this, I've merged the commit that you're using that chooses the middle anchor,

genetracks/src/genetracks/elements.py

Line 66 in 4e3b05f

text_anchor="middle",

but not logic for choosing the anchor. Is the text positioning still a problem? Or will we need some logic to switch the anchor?