From d5f834d20d4710df857f4ea1b20d2261e027caac Mon Sep 17 00:00:00 2001
From: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>
Date: Mon, 4 Sep 2023 22:05:58 +0200
Subject: [PATCH] Add `TextFormat::extra_letter_spacing`

---
 crates/egui/src/widget_text.rs                | 12 +++++++
 .../src/easy_mark/easy_mark_highlighter.rs    |  1 +
 crates/epaint/src/text/text_layout.rs         | 23 ++++++++-----
 crates/epaint/src/text/text_layout_types.rs   | 33 ++++++++++++++++++-
 4 files changed, 60 insertions(+), 9 deletions(-)

diff --git a/crates/egui/src/widget_text.rs b/crates/egui/src/widget_text.rs
index 3d252cb21bba..807afac39bdd 100644
--- a/crates/egui/src/widget_text.rs
+++ b/crates/egui/src/widget_text.rs
@@ -25,6 +25,7 @@ use crate::{
 pub struct RichText {
     text: String,
     size: Option<f32>,
+    extra_letter_spacing: f32,
     family: Option<FontFamily>,
     text_style: Option<TextStyle>,
     background_color: Color32,
@@ -100,6 +101,15 @@ impl RichText {
         self
     }
 
+    /// Extra spacing between letters, in points.
+    ///
+    /// Default: 0.0. Round to whole _pixels_ for crisp text.
+    #[inline]
+    pub fn extra_letter_spacing(mut self, extra_letter_spacing: f32) -> Self {
+        self.extra_letter_spacing = extra_letter_spacing;
+        self
+    }
+
     /// Select the font family.
     ///
     /// This overrides the value from [`Self::text_style`].
@@ -253,6 +263,7 @@ impl RichText {
         let Self {
             text,
             size,
+            extra_letter_spacing,
             family,
             text_style,
             background_color,
@@ -315,6 +326,7 @@ impl RichText {
             underline,
             strikethrough,
             valign,
+            extra_letter_spacing,
         };
 
         let job = LayoutJob::single_section(text, text_format);
diff --git a/crates/egui_demo_lib/src/easy_mark/easy_mark_highlighter.rs b/crates/egui_demo_lib/src/easy_mark/easy_mark_highlighter.rs
index c15a285b9c66..7431accc5045 100644
--- a/crates/egui_demo_lib/src/easy_mark/easy_mark_highlighter.rs
+++ b/crates/egui_demo_lib/src/easy_mark/easy_mark_highlighter.rs
@@ -188,5 +188,6 @@ fn format_from_style(
         underline,
         strikethrough,
         valign,
+        ..Default::default()
     }
 }
diff --git a/crates/epaint/src/text/text_layout.rs b/crates/epaint/src/text/text_layout.rs
index 5aab349e2cd9..726abc0e3435 100644
--- a/crates/epaint/src/text/text_layout.rs
+++ b/crates/epaint/src/text/text_layout.rs
@@ -136,6 +136,7 @@ fn layout_section(
                     paragraph.cursor_x += font_impl.pair_kerning(last_glyph_id, glyph_info.id);
                 }
             }
+            paragraph.cursor_x += section.format.extra_letter_spacing;
 
             paragraph.glyphs.push(Glyph {
                 chr,
@@ -338,10 +339,13 @@ fn replace_last_glyph_with_overflow_character(
 
         // undo kerning with previous glyph
         let (font_impl, glyph_info) = font.glyph_info_and_font_impl(last_glyph.chr);
-        last_glyph.pos.x -= font_impl
-            .zip(prev_glyph_id)
-            .map(|(font_impl, prev_glyph_id)| font_impl.pair_kerning(prev_glyph_id, glyph_info.id))
-            .unwrap_or_default();
+        last_glyph.pos.x -= section.format.extra_letter_spacing
+            + font_impl
+                .zip(prev_glyph_id)
+                .map(|(font_impl, prev_glyph_id)| {
+                    font_impl.pair_kerning(prev_glyph_id, glyph_info.id)
+                })
+                .unwrap_or_default();
 
         // replace the glyph
         last_glyph.chr = overflow_character;
@@ -351,10 +355,13 @@ fn replace_last_glyph_with_overflow_character(
         last_glyph.ascent = glyph_info.ascent;
 
         // reapply kerning
-        last_glyph.pos.x += font_impl
-            .zip(prev_glyph_id)
-            .map(|(font_impl, prev_glyph_id)| font_impl.pair_kerning(prev_glyph_id, glyph_info.id))
-            .unwrap_or_default();
+        last_glyph.pos.x += section.format.extra_letter_spacing
+            + font_impl
+                .zip(prev_glyph_id)
+                .map(|(font_impl, prev_glyph_id)| {
+                    font_impl.pair_kerning(prev_glyph_id, glyph_info.id)
+                })
+                .unwrap_or_default();
 
         row.rect.max.x = last_glyph.max_x();
 
diff --git a/crates/epaint/src/text/text_layout_types.rs b/crates/epaint/src/text/text_layout_types.rs
index 2a73bd60f8b2..b19806aa5e4b 100644
--- a/crates/epaint/src/text/text_layout_types.rs
+++ b/crates/epaint/src/text/text_layout_types.rs
@@ -221,11 +221,17 @@ impl std::hash::Hash for LayoutSection {
 
 // ----------------------------------------------------------------------------
 
-#[derive(Clone, Debug, Hash, PartialEq)]
+/// Formatting option for a section of text.
+#[derive(Clone, Debug, PartialEq)]
 #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
 pub struct TextFormat {
     pub font_id: FontId,
 
+    /// Extra spacing between letters, in points.
+    ///
+    /// Default: 0.0. Round to whole _pixels_ for crisp text.
+    pub extra_letter_spacing: f32,
+
     /// Text color
     pub color: Color32,
 
@@ -243,6 +249,30 @@ pub struct TextFormat {
     // TODO(emilk): lowered
 }
 
+impl std::hash::Hash for TextFormat {
+    #[inline]
+    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
+        let Self {
+            font_id,
+            extra_letter_spacing,
+            color,
+            background,
+            italics,
+            underline,
+            strikethrough,
+            valign,
+        } = self;
+        font_id.hash(state);
+        crate::f32_hash(state, *extra_letter_spacing);
+        color.hash(state);
+        background.hash(state);
+        italics.hash(state);
+        underline.hash(state);
+        strikethrough.hash(state);
+        valign.hash(state);
+    }
+}
+
 impl Default for TextFormat {
     #[inline]
     fn default() -> Self {
@@ -254,6 +284,7 @@ impl Default for TextFormat {
             underline: Stroke::NONE,
             strikethrough: Stroke::NONE,
             valign: Align::BOTTOM,
+            extra_letter_spacing: 0.0,
         }
     }
 }