Snap to Glyph: the x-height guide stays on the glyphs' x-height

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.

crates/text/src/layout.rs

@@ -216,6 +216,12 @@ impl Ctx<'_> {
                 Affine::rotate(-g.rotation.to_radians()) * Affine::translate((g.dx - lead, g.dy - g.bshift)) * Affine::scale_non_uniform(g.sx, g.sy)
             }
         };
+        let unturned = if g.inline.is_none() && g.rotation != 0.0 && g.sx != 0.0 && g.sy != 0.0 {
+            let placed = Affine::translate((g.dx - lead, g.dy - g.bshift)) * Affine::scale_non_uniform(g.sx, g.sy);
+            placed.inverse() * Affine::rotate(g.rotation.to_radians()) * placed
+        } else {
+            Affine::IDENTITY
+        };
         let mut m = pre * local;
         if self.vertical && self.on_path {
             // Vertical path type keeps the baseline path and turns each glyph across it.
@@ -271,6 +277,7 @@ impl Ctx<'_> {
             image,
             colour,
             bend: None,
+            unturned,
         });
     }
 

crates/text/src/layout/ruby.rs

@@ -367,5 +367,6 @@ fn ruby_glyph(g: &PositionedGlyph, m: Affine, run: usize, byte: usize, line: usi
         image: None,
         colour: None,
         bend: None,
+        unturned: Affine::IDENTITY,
     }
 }

crates/text/src/lib.rs

@@ -136,6 +136,9 @@ pub struct PositionedGlyph {
     /// the path ([`GlyphBend`]) so it meets its neighbours, and `xf` is only the straight glyph
     /// nearest it (for the caret, hit testing and tools). `None`: the glyph is drawn through `xf`.
     pub bend: Option<GlyphBend>,
+    /// Font units → font units: `xf * unturned` places the glyph as it would be placed without
+    /// its Character Rotation. The identity for a glyph without one.
+    pub unturned: Affine,
 }
 
 /// How a glyph on a path is bent along it: a point of its pen space (x along its advance from its

crates/text/src/tests/bidi.rs

@@ -163,6 +163,7 @@ fn lines_of_clusters(lines: &[&[(usize, usize, f64)]], rtl: bool) -> TextLayout
                 image: None,
                 colour: None,
                 bend: None,
+                unturned: Affine::IDENTITY,
             });
             x += advance;
         }