Save range of original text in glyph

[LaurenzV]

Okay, so I tried to look into #109 myself, and it actually was very straighforward (I tested it and it seems to work for my purpose), however:

• I had to make Glyph not implement copy, since Range doesn't.
• I'm a bit unsure why I had to add the text range in two places instead of one and I'm not sure it's 100% correct, so I would appreciate if someone could check this in detail to make sure I didn't mess up anything (assuming that you are okay with this change in the first place). :p

[dfrg]

Parley goes to great lengths to keep compact data structures in layout so I’d strongly prefer to not double the size of Glyph.

Given what you’ve done here, I wonder if something like this might work for you:

for run in line.runs() {
    for cluster in run.visual_clusters() {
        let range = cluster.text_range();
        for glyph in cluster.glyphs() {
            // here we have glyph and source range
            // but have to handle styles manually
        }
    }
}

This basically avoids GlyphRun entirely so you’d need to handle intra cluster style changes yourself. Each glyph has a style_index which refers to the slice returned by layout.styles().

[LaurenzV]

Totally understandable, I'll give this a try later, thanks!