Character Rotation turned a glyph's baseline shift and scaling with the glyph, and the Skew path effect slants a glyph's height away from the path's normal, so the x-height guide moved off the glyphs. Each positioned glyph now carries the transform that removes its Character Rotation (PositionedGlyph::unturned), and the guide goes through the glyph's x-height point placed without it, measured across the baseline. Snap to Glyph also takes Smart Guides being on in the tools, as View › Snap to Glyph already does in the engine.
With View › Snap to Glyph and Smart Guides on, a point drawn near a single
line of live type now also lands on the anchor points of its glyphs and lines
up with its x-height (raised or lowered by Baseline Shift) and with the edges
of each character's advance width along the baseline (proximity guides). In
rotated type the baseline, x-height and proximity guides run at the type's
angle, and type of one glyph also has angular guides along the glyph's slanted
straight segments; a segment that Shift keeps to its angle slides onto them.
A paragraph shows glyph bounds only, so its baselines are no longer guides.
FontFace::x_height gives a face's x-height in font units.
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