From 8a33a6a6ce48fb95e5e8334e725e2d2794b6d804 Mon Sep 17 00:00:00 2001
From: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>
Date: Sun, 30 Mar 2025 20:03:47 +0200
Subject: [PATCH] Make the section index private so we don't need to calculate
 it corectly

---
 crates/epaint/src/text/fonts.rs             | 16 ++++++-------
 crates/epaint/src/text/text_layout.rs       |  9 +++-----
 crates/epaint/src/text/text_layout_types.rs | 25 +++++++++------------
 3 files changed, 22 insertions(+), 28 deletions(-)

diff --git a/crates/epaint/src/text/fonts.rs b/crates/epaint/src/text/fonts.rs
index f92c5c103..c78ca99a6 100644
--- a/crates/epaint/src/text/fonts.rs
+++ b/crates/epaint/src/text/fonts.rs
@@ -1094,17 +1094,17 @@ mod tests {
 
                         for (i, row) in whole.rows.iter().enumerate() {
                             println!(
-                        "Whole row {i}: section_index_at_start={}, first glyph section_index: {:?}",
-                        row.row.section_index_at_start,
-                        row.row.glyphs.first().map(|g| g.section_index)
-                    );
+                                "Whole row {i}: section_index_at_start={}, first glyph section_index: {:?}",
+                                row.row.section_index_at_start,
+                                row.row.glyphs.first().map(|g| g.section_index)
+                            );
                         }
                         for (i, row) in split.rows.iter().enumerate() {
                             println!(
-                        "Split row {i}: section_index_at_start={}, first glyph section_index: {:?}",
-                        row.row.section_index_at_start,
-                        row.row.glyphs.first().map(|g| g.section_index)
-                    );
+                                "Split row {i}: section_index_at_start={}, first glyph section_index: {:?}",
+                                row.row.section_index_at_start,
+                                row.row.glyphs.first().map(|g| g.section_index)
+                            );
                         }
 
                         // Don't compare for equaliity; but format with a specific precision and make sure we hit that.
diff --git a/crates/epaint/src/text/text_layout.rs b/crates/epaint/src/text/text_layout.rs
index 26bf6860c..b2dba96fc 100644
--- a/crates/epaint/src/text/text_layout.rs
+++ b/crates/epaint/src/text/text_layout.rs
@@ -664,13 +664,10 @@ fn galley_from_rows(
             mesh_bounds.union(row.visuals.mesh_bounds.translate(placed_row.pos.to_vec2()));
         num_vertices += row.visuals.mesh.vertices.len();
         num_indices += row.visuals.mesh.indices.len();
-    }
 
-    // Fill in correct section_index_at_start for each row:
-    for placed in &mut rows {
-        let row = Arc::make_mut(&mut placed.row);
-        if let Some(first_glyph) = row.glyphs.first_mut() {
-            row.section_index_at_start = first_glyph.section_index;
+        row.section_index_at_start = u32::MAX; // No longer in use.
+        for glyph in &mut row.glyphs {
+            glyph.section_index = u32::MAX; // No longer in use.
         }
     }
 
diff --git a/crates/epaint/src/text/text_layout_types.rs b/crates/epaint/src/text/text_layout_types.rs
index 5ee1fe142..c1e54b35a 100644
--- a/crates/epaint/src/text/text_layout_types.rs
+++ b/crates/epaint/src/text/text_layout_types.rs
@@ -578,8 +578,12 @@ impl std::ops::Deref for PlacedRow {
 #[derive(Clone, Debug, PartialEq)]
 #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
 pub struct Row {
-    /// This is included in case there are no glyphs
-    pub section_index_at_start: u32,
+    /// This is included in case there are no glyphs.
+    ///
+    /// Only used during layout, then set to an invalid value in order to
+    /// enable the paragraph-concat optimization path without having to
+    /// adjust `section_index` when concatting.
+    pub(crate) section_index_at_start: u32,
 
     /// One for each `char`.
     pub glyphs: Vec<Glyph>,
@@ -669,7 +673,11 @@ pub struct Glyph {
     pub uv_rect: UvRect,
 
     /// Index into [`LayoutJob::sections`]. Decides color etc.
-    pub section_index: u32,
+    ///
+    /// Only used during layout, then set to an invalid value in order to
+    /// enable the paragraph-concat optimization path without having to
+    /// adjust `section_index` when concatting.
+    pub(crate) section_index: u32,
 }
 
 impl Glyph {
@@ -841,17 +849,6 @@ impl Galley {
             merged_galley.elided |= galley.elided;
         }
 
-        for placed in &mut merged_galley.rows {
-            let section_index_at_start = placed.row.glyphs.first().map(|g| g.section_index);
-            if let Some(section_index_at_start) = section_index_at_start {
-                if placed.row.section_index_at_start != section_index_at_start {
-                    // This `make_mut` is slow, so only do it when necessary.
-                    let row = Arc::make_mut(&mut placed.row);
-                    row.section_index_at_start = section_index_at_start;
-                }
-            }
-        }
-
         if merged_galley.job.round_output_to_gui {
             merged_galley.round_output_to_gui();
         }