Improve modern layout and viewport rendering

crates/obscura-render/Cargo.toml

@@ -11,7 +11,7 @@ default = []
 # Rasterize the laid-out tree to a pixmap (tiny-skia) with text (cosmic-text
 # shaping + line breaking, ab_glyph fallback) and images.
 # Off by default; the layout core (getBoundingClientRect etc.) works without it.
-paint = ["dep:tiny-skia", "dep:ab_glyph", "dep:cosmic-text", "dep:image", "dep:ureq", "dep:base64", "dep:resvg", "dep:usvg", "dep:url", "dep:wuff"]
+paint = ["dep:tiny-skia", "dep:ab_glyph", "dep:cosmic-text", "dep:swash", "dep:image", "dep:ureq", "dep:base64", "dep:resvg", "dep:usvg", "dep:url", "dep:wuff"]
 
 [dependencies]
 taffy = { workspace = true }
@@ -22,6 +22,10 @@ ab_glyph = { workspace = true, optional = true }
 # breaking, the same algorithms browsers use. Built with only our embedded
 # fonts (no system-font scan) so layout stays deterministic across hosts.
 cosmic-text = { version = "=0.12.1", default-features = false, features = ["std", "swash"], optional = true }
+# Keep this exactly aligned with cosmic-text 0.12's raster backend. Cosmic
+# does not expose variation coordinates, so variable font instances are
+# rasterized through Swash directly while Cosmic remains the shaper.
+swash = { version = "=0.1.19", optional = true }
 image = { version = "0.25", default-features = false, features = ["jpeg", "png", "webp"], optional = true }
 ureq = { version = "2.9", default-features = false, features = ["tls"], optional = true }
 base64 = { workspace = true, optional = true }