Make text flattening lazy - #1124
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Parsing now only performs text layout. Glyph outlines are computed on first access to Text::flattened, or upfront for the whole tree via the new Tree::compute_flattened_text, which shares an ephemeral glyph cache between all text nodes. Text::stroke_bounding_box is now approximated at layout time from the per-glyph ink bounding boxes stored in the font.
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usvg's flattening of glyphs into sub-SVGs is inefficient (it writes out the glyphs paths as an SVG string and then re-parses them!), and is not required by users ofusvgthat are capable of rendering glyphs themselves. But currently on main, if you have thetextfeature (necessary to get layouted text) then glyphs will always be flattened.This PR changes text flattening to be lazy (using a
OnceLock), so you only pay that cost if you need the flattened glyphs:Text::flattened, or upfront for the whole tree via the newTree::compute_flattened_text(the latter approach is more efficient as it shares an ephemeral glyph cache between all text nodes)Text::stroke_bounding_boxis now approximated at layout time from the per-glyph ink bounding boxes stored in the font.Generated with Fable. Has been through a couple of iterations, but has not yet be thoroughly self-reviewed.