Simplify shaping 🌱

2 files changed, 63 insertions, 113 deletions

diff --git a/src/layout/tree.rs b/src/layout/tree.rs
index fde7833e..c5b6609b 100644
--- a/src/layout/tree.rs
+++ b/src/layout/tree.rs
@@ -116,11 +116,11 @@ impl<'a> TreeLayouter<'a> {
 
         let boxed = shaping::shape(
             text,
-            self.ctx.state.sys.primary,
             self.ctx.state.text.font_size(),
-            variant,
-            &self.ctx.state.text.fallback,
+            self.ctx.state.sys.primary,
             &mut self.ctx.loader.borrow_mut(),
+            &self.ctx.state.text.fallback,
+            variant,
         )
         .await;
 
diff --git a/src/shaping.rs b/src/shaping.rs
index 7c60e0d2..c620f872 100644
--- a/src/shaping.rs
+++ b/src/shaping.rs
@@ -7,24 +7,12 @@
 use std::fmt::{self, Debug, Formatter};
 
 use fontdock::{FaceId, FaceQuery, FallbackTree, FontVariant};
-use ttf_parser::GlyphId;
+use ttf_parser::{Face, GlyphId};
 
 use crate::font::FontLoader;
 use crate::geom::{Point, Size};
 use crate::layout::{BoxLayout, Dir, LayoutElement};
 
-/// Shape text into a box containing shaped runs.
-pub async fn shape(
-    text: &str,
-    dir: Dir,
-    size: f64,
-    variant: FontVariant,
-    fallback: &FallbackTree,
-    loader: &mut FontLoader,
-) -> BoxLayout {
-    Shaper::new(text, dir, size, variant, fallback, loader).shape().await
-}
-
 /// A shaped run of text.
 #[derive(Clone, PartialEq)]
 pub struct Shaped {
@@ -70,113 +58,75 @@ impl Debug for Shaped {
     }
 }
 
-/// Performs super-basic text shaping.
-struct Shaper<'a> {
-    text: &'a str,
+/// Shape text into a box containing [`Shaped`] runs.
+///
+/// [`Shaped`]: struct.Shaped.html
+pub async fn shape(
+    text: &str,
+    size: f64,
     dir: Dir,
+    loader: &mut FontLoader,
+    fallback: &FallbackTree,
     variant: FontVariant,
-    fallback: &'a FallbackTree,
-    loader: &'a mut FontLoader,
-    shaped: Shaped,
-    layout: BoxLayout,
-    offset: f64,
-}
-
-impl<'a> Shaper<'a> {
-    fn new(
-        text: &'a str,
-        dir: Dir,
-        size: f64,
-        variant: FontVariant,
-        fallback: &'a FallbackTree,
-        loader: &'a mut FontLoader,
-    ) -> Self {
-        Self {
-            text,
-            dir,
-            variant,
-            fallback,
-            loader,
-            shaped: Shaped::new(FaceId::MAX, size),
-            layout: BoxLayout::new(Size::new(0.0, size)),
-            offset: 0.0,
-        }
-    }
-
-    async fn shape(mut self) -> BoxLayout {
-        // If the primary axis is negative, we layout the characters reversed.
-        if self.dir.is_positive() {
-            for c in self.text.chars() {
-                self.shape_char(c).await;
-            }
-        } else {
-            for c in self.text.chars().rev() {
-                self.shape_char(c).await;
+) -> BoxLayout {
+    let mut layout = BoxLayout::new(Size::new(0.0, size));
+    let mut shaped = Shaped::new(FaceId::MAX, size);
+    let mut offset = 0.0;
+
+    // Create an iterator with conditional direction.
+    let mut forwards = text.chars();
+    let mut backwards = text.chars().rev();
+    let chars: &mut dyn Iterator<Item = char> = if dir.is_positive() {
+        &mut forwards
+    } else {
+        &mut backwards
+    };
+
+    for c in chars {
+        let query = FaceQuery { fallback: fallback.iter(), variant, c };
+        if let Some((id, owned_face)) = loader.query(query).await {
+            let face = owned_face.get();
+            let (glyph, width) = match lookup_glyph(face, c, size) {
+                Some(v) => v,
+                None => continue,
+            };
+
+            // Flush the buffer if we change the font face.
+            if shaped.face != id && !shaped.text.is_empty() {
+                let pos = Point::new(layout.size.width, 0.0);
+                layout.push(pos, LayoutElement::Text(shaped));
+                layout.size.width += offset;
+                shaped = Shaped::new(FaceId::MAX, size);
+                offset = 0.0;
             }
-        }
 
-        // Flush the last buffered parts of the word.
-        if !self.shaped.text.is_empty() {
-            let pos = Point::new(self.offset, 0.0);
-            self.layout.push(pos, LayoutElement::Text(self.shaped));
+            shaped.face = id;
+            shaped.text.push(c);
+            shaped.glyphs.push(glyph);
+            shaped.offsets.push(offset);
+            offset += width;
         }
-
-        self.layout
     }
 
-    async fn shape_char(&mut self, c: char) {
-        let (index, glyph, char_width) = match self.select_font(c).await {
-            Some(selected) => selected,
-            // TODO: Issue warning about missing character.
-            None => return,
-        };
-
-        // Flush the buffer and issue a font setting action if the font differs
-        // from the last character's one.
-        if self.shaped.face != index {
-            if !self.shaped.text.is_empty() {
-                let shaped = std::mem::replace(
-                    &mut self.shaped,
-                    Shaped::new(FaceId::MAX, self.layout.size.height),
-                );
-
-                let pos = Point::new(self.offset, 0.0);
-                self.layout.push(pos, LayoutElement::Text(shaped));
-                self.offset = self.layout.size.width;
-            }
-
-            self.shaped.face = index;
-        }
-
-        self.shaped.text.push(c);
-        self.shaped.glyphs.push(glyph);
-        self.shaped.offsets.push(self.layout.size.width - self.offset);
-
-        self.layout.size.width += char_width;
+    // Flush the last buffered parts of the word.
+    if !shaped.text.is_empty() {
+        let pos = Point::new(layout.size.width, 0.0);
+        layout.push(pos, LayoutElement::Text(shaped));
+        layout.size.width += offset;
     }
 
-    async fn select_font(&mut self, c: char) -> Option<(FaceId, GlyphId, f64)> {
-        let query = FaceQuery {
-            fallback: self.fallback.iter(),
-            variant: self.variant,
-            c,
-        };
-
-        if let Some((id, owned_face)) = self.loader.query(query).await {
-            let face = owned_face.get();
+    layout
+}
 
-            let units_per_em = face.units_per_em().unwrap_or(1000) as f64;
-            let ratio = 1.0 / units_per_em;
-            let font_size = self.layout.size.height;
-            let to_raw = |x| ratio * x as f64 * font_size;
+/// Looks up the glyph for `c` and returns its index alongside its width at the
+/// given `size`.
+fn lookup_glyph(face: &Face, c: char, size: f64) -> Option<(GlyphId, f64)> {
+    let glyph = face.glyph_index(c)?;
 
-            // Determine the width of the char.
-            let glyph = face.glyph_index(c)?;
-            let glyph_width = to_raw(face.glyph_hor_advance(glyph)? as i32);
+    // Determine the width of the char.
+    let units_per_em = face.units_per_em().unwrap_or(1000) as f64;
+    let width_units = face.glyph_hor_advance(glyph)? as f64;
+    let width = width_units / units_per_em * size;
 
-            Some((id, glyph, glyph_width))
-        } else {
-            None
-        }
-    }
+    Some((glyph, width))
 }