How can I convert a stroke to an outlined object in Inkscape?

Question

I have an SVG file with some stroked paths in it (exported from a Cairo program), which I'm editing in Inkscape.

I want to import it into FontForge, but for that, I need these to be filled paths—that is, I need to create the path that makes an outline around this shape, and fill that.

This seems like it should be a job for Path > Stroke to Path, but when I do that, it gets distorted.

From searching online, it seems like the solution is to use Path > Break Apart first (to split it into individual paths), then Path > Union afterward. But when I use Path > Break Apart, everything goes wrong:

Yikes! This isn't the shape I want! It seems like Break Apart is getting rid of the style of the path, so it ends up with a black fill and no stroke.

Why is Break Apart doing this? I've made sure my path isn't in a group, for starters, but I don't know what else to try.

Or, am I on the wrong track, and there's a different and better way to turn a stroked path into an identical-looking filled path?

Answer 1

This is bizarre, and I think arguably a bug in Inkscape!

In an SVG file, there are two different ways to specify the properties of a <path>. One is to use a bunch of different properties, stroke-width="0.05" stroke-linecap="round" and so on. The other is to consolidate all of those into a single style property, style="stroke-width:0.05;stroke-linecap:round;".

Inkscape seems to handle them both just fine. But if you open an SVG file that uses the first style, with separate properties, they aren't quite imported right! They'll seem to work, but any path operations (like the Break Apart I was trying to do) will lose all of those properties.

The solution is to make sure all SVG files you open in Inkscape use the second style, in which case the properties will actually be set correctly and will survive path operations. So now I have a Python script that modifies the SVG file before I import it:

import lxml.etree as et

def clean_xml(file):
    SAFE_ATTRS = {'d', 'transform', 'style'} # The attributes we don't want to change
    tree = et.parse(file)
    for path in tree.getroot().iter():
        if not path.tag.endswith('path'): continue
        if 'style' in path.attrib: continue # Already has a style
        style = []
        iterator = list(path.attrib.items()) # So we can edit while iterating
        for key, val in iterator:
            if key in SAFE_ATTRS: continue
            style.append(f'{key}:{val};')
            del path.attrib[key]
        path.attrib['style'] = ''.join(style)
    tree.write(file)