Add byte information to PositionedGlyph (#17900)

# Objective

Adds information about the byte length and index of a glyph to
`PositionedGlyph`. Useful for text picking, allows for picking with
multi-byte characters. Also adds a `line` field that helps with
converting back and forth from cosmic's `Cursor`.

## Solution

Retrieve the relevant data from cosmic and add it to the glyph in the
text pipeline.

## Testing

`cargo r -p ci`

---

## Migration Guide

`PositionedGlyph::new()` has been removed as there is no longer an
unused field. Create new `PositionedGlyph`s directly.

crates/bevy_text/src/glyph.rs

@@ -20,24 +20,12 @@ pub struct PositionedGlyph {
     pub atlas_info: GlyphAtlasInfo,
     /// The index of the glyph in the [`ComputedTextBlock`](crate::ComputedTextBlock)'s tracked spans.
     pub span_index: usize,
-    /// TODO: In order to do text editing, we need access to the size of glyphs and their index in the associated String.
+    /// The index of the glyph's line.
-    /// For example, to figure out where to place the cursor in an input box from the mouse's position.
+    pub line_index: usize,
-    /// Without this, it's only possible in texts where each glyph is one byte. Cosmic text has methods for this
+    /// The byte index of the glyph in it's line.
-    /// cosmic-texts [hit detection](https://pop-os.github.io/cosmic-text/cosmic_text/struct.Buffer.html#method.hit)
+    pub byte_index: usize,
-    byte_index: usize,
+    /// The byte length of the glyph.
-}
+    pub byte_length: usize,
-
-impl PositionedGlyph {
-    /// Creates a new [`PositionedGlyph`]
-    pub fn new(position: Vec2, size: Vec2, atlas_info: GlyphAtlasInfo, span_index: usize) -> Self {
-        Self {
-            position,
-            size,
-            atlas_info,
-            span_index,
-            byte_index: 0,
-        }
-    }
 }
 
 /// Information about a glyph in an atlas.

crates/bevy_text/src/pipeline.rs

@@ -263,14 +263,12 @@ impl TextPipeline {
         let buffer = &mut computed.buffer;
         let box_size = buffer_dimensions(buffer);
 
-        let result = buffer
+        let result = buffer.layout_runs().try_for_each(|run| {
-            .layout_runs()
+            let result = run
-            .flat_map(|run| {
+                .glyphs
-                run.glyphs
                 .iter()
-                    .map(move |layout_glyph| (layout_glyph, run.line_y))
+                .map(move |layout_glyph| (layout_glyph, run.line_y, run.line_i))
-            })
+                .try_for_each(|(layout_glyph, line_y, line_i)| {
-            .try_for_each(|(layout_glyph, line_y)| {
                     let mut temp_glyph;
                     let span_index = layout_glyph.metadata;
                     let font_id = glyph_info[span_index].0;
@@ -319,7 +317,8 @@ impl TextPipeline {
 
                     // offset by half the size because the origin is center
                     let x = glyph_size.x as f32 / 2.0 + left + physical_glyph.x as f32;
-                let y = line_y.round() + physical_glyph.y as f32 - top + glyph_size.y as f32 / 2.0;
+                    let y =
+                        line_y.round() + physical_glyph.y as f32 - top + glyph_size.y as f32 / 2.0;
                     let y = match y_axis_orientation {
                         YAxisOrientation::TopToBottom => y,
                         YAxisOrientation::BottomToTop => box_size.y - y,
@@ -327,14 +326,22 @@ impl TextPipeline {
 
                     let position = Vec2::new(x, y);
 
-                // TODO: recreate the byte index, that keeps track of where a cursor is,
+                    let pos_glyph = PositionedGlyph {
-                // when glyphs are not limited to single byte representation, relevant for #1319
+                        position,
-                let pos_glyph =
+                        size: glyph_size.as_vec2(),
-                    PositionedGlyph::new(position, glyph_size.as_vec2(), atlas_info, span_index);
+                        atlas_info,
+                        span_index,
+                        byte_index: layout_glyph.start,
+                        byte_length: layout_glyph.end - layout_glyph.start,
+                        line_index: line_i,
+                    };
                     layout_info.glyphs.push(pos_glyph);
                     Ok(())
                 });
 
+            result
+        });
+
         // Return the scratch vec.
         self.glyph_info = glyph_info;