Add control of line height

crates/egui/src/widget_text.rs

@@ -1,5 +1,4 @@
-use std::borrow::Cow;
-use std::sync::Arc;
+use std::{borrow::Cow, sync::Arc};
 
 use crate::{
     style::WidgetVisuals, text::LayoutJob, Align, Color32, FontFamily, FontSelection, Galley, Pos2,
@@ -26,6 +25,7 @@ pub struct RichText {
     text: String,
     size: Option<f32>,
     extra_letter_spacing: f32,
+    line_height: Option<f32>,
     family: Option<FontFamily>,
     text_style: Option<TextStyle>,
     background_color: Color32,
@@ -110,6 +110,19 @@ impl RichText {
         self
     }
 
+    /// Explicit line height of the text in points.
+    ///
+    /// This is the distance between the bottom row of two subsequent lines of text.
+    ///
+    /// If `None` (the default), the line height is determined by the font.
+    ///
+    /// Round to whole _pixels_ for crisp text.
+    #[inline]
+    pub fn line_height(mut self, line_height: Option<f32>) -> Self {
+        self.line_height = line_height;
+        self
+    }
+
     /// Select the font family.
     ///
     /// This overrides the value from [`Self::text_style`].
@@ -264,6 +277,7 @@ impl RichText {
             text,
             size,
             extra_letter_spacing,
+            line_height,
             family,
             text_style,
             background_color,
@@ -320,13 +334,14 @@ impl RichText {
 
         let text_format = crate::text::TextFormat {
             font_id,
+            extra_letter_spacing,
+            line_height,
             color: text_color,
             background: background_color,
             italics,
             underline,
             strikethrough,
             valign,
-            extra_letter_spacing,
         };
 
         let job = LayoutJob::single_section(text, text_format);

crates/epaint/src/text/font.rs

@@ -49,11 +49,6 @@ pub struct GlyphInfo {
     /// Unit: points.
     pub ascent: f32,
 
-    /// row height computed from the font metrics.
-    ///
-    /// Unit: points.
-    pub row_height: f32,
-
     /// Texture coordinates.
     pub uv_rect: UvRect,
 }
@@ -65,7 +60,6 @@ impl Default for GlyphInfo {
             id: ab_glyph::GlyphId(0),
             advance_width: 0.0,
             ascent: 0.0,
-            row_height: 0.0,
             uv_rect: Default::default(),
         }
     }
@@ -250,7 +244,7 @@ impl FontImpl {
             / self.pixels_per_point
     }
 
-    /// Height of one row of text. In points
+    /// Height of one row of text in points.
     #[inline(always)]
     pub fn row_height(&self) -> f32 {
         self.height_in_points
@@ -312,7 +306,6 @@ impl FontImpl {
             id: glyph_id,
             advance_width: advance_width_in_points,
             ascent: self.ascent,
-            row_height: self.row_height(),
             uv_rect,
         }
     }

crates/epaint/src/text/fonts.rs

@@ -653,7 +653,7 @@ impl FontsImpl {
         self.font(font_id).has_glyphs(s)
     }
 
-    /// Height of one row of text. In points
+    /// Height of one row of text in points.
     fn row_height(&mut self, font_id: &FontId) -> f32 {
         self.font(font_id).row_height()
     }

crates/epaint/src/text/text_layout.rs

@@ -113,11 +113,14 @@ fn layout_section(
         format,
     } = section;
     let font = fonts.font(&format.font_id);
-    let font_height = font.row_height();
+    let line_height = section
+        .format
+        .line_height
+        .unwrap_or_else(|| font.row_height());
 
     let mut paragraph = out_paragraphs.last_mut().unwrap();
     if paragraph.glyphs.is_empty() {
-        paragraph.empty_paragraph_height = font_height; // TODO(emilk): replace this hack with actually including `\n` in the glyphs?
+        paragraph.empty_paragraph_height = line_height; // TODO(emilk): replace this hack with actually including `\n` in the glyphs?
     }
 
     paragraph.cursor_x += leading_space;
@@ -128,7 +131,7 @@ fn layout_section(
         if job.break_on_newline && chr == '\n' {
             out_paragraphs.push(Paragraph::default());
             paragraph = out_paragraphs.last_mut().unwrap();
-            paragraph.empty_paragraph_height = font_height; // TODO(emilk): replace this hack with actually including `\n` in the glyphs?
+            paragraph.empty_paragraph_height = line_height; // TODO(emilk): replace this hack with actually including `\n` in the glyphs?
         } else {
             let (font_impl, glyph_info) = font.glyph_info_and_font_impl(chr);
             if let Some(font_impl) = font_impl {
@@ -141,7 +144,7 @@ fn layout_section(
             paragraph.glyphs.push(Glyph {
                 chr,
                 pos: pos2(paragraph.cursor_x, f32::NAN),
-                size: vec2(glyph_info.advance_width, glyph_info.row_height),
+                size: vec2(glyph_info.advance_width, line_height),
                 ascent: glyph_info.ascent,
                 uv_rect: glyph_info.uv_rect,
                 section_index,
@@ -330,7 +333,10 @@ fn replace_last_glyph_with_overflow_character(
 
         let section = &job.sections[last_glyph.section_index as usize];
         let font = fonts.font(&section.format.font_id);
-        let font_height = font.row_height();
+        let line_height = section
+            .format
+            .line_height
+            .unwrap_or_else(|| font.row_height());
 
         let prev_glyph_id = prev_glyph.map(|prev_glyph| {
             let (_, prev_glyph_info) = font.glyph_info_and_font_impl(prev_glyph.chr);
@@ -350,7 +356,7 @@ fn replace_last_glyph_with_overflow_character(
         // replace the glyph
         last_glyph.chr = overflow_character;
         let (font_impl, glyph_info) = font.glyph_info_and_font_impl(last_glyph.chr);
-        last_glyph.size = vec2(glyph_info.advance_width, font_height);
+        last_glyph.size = vec2(glyph_info.advance_width, line_height);
         last_glyph.uv_rect = glyph_info.uv_rect;
         last_glyph.ascent = glyph_info.ascent;
 
@@ -481,7 +487,7 @@ fn galley_from_rows(
     let mut min_x: f32 = 0.0;
     let mut max_x: f32 = 0.0;
     for row in &mut rows {
-        let mut row_height = first_row_min_height.max(row.rect.height());
+        let mut line_height = first_row_min_height.max(row.rect.height());
         let mut row_ascent = 0.0f32;
         first_row_min_height = 0.0;
 
@@ -491,10 +497,10 @@ fn galley_from_rows(
             .iter()
             .max_by(|a, b| a.size.y.partial_cmp(&b.size.y).unwrap())
         {
-            row_height = glyph.size.y;
+            line_height = glyph.size.y;
             row_ascent = glyph.ascent;
         }
-        row_height = point_scale.round_to_pixel(row_height);
+        line_height = point_scale.round_to_pixel(line_height);
 
         // Now positions each glyph:
         for glyph in &mut row.glyphs {
@@ -510,11 +516,11 @@ fn galley_from_rows(
         }
 
         row.rect.min.y = cursor_y;
-        row.rect.max.y = cursor_y + row_height;
+        row.rect.max.y = cursor_y + line_height;
 
         min_x = min_x.min(row.rect.min.x);
         max_x = max_x.max(row.rect.max.x);
-        cursor_y += row_height;
+        cursor_y += line_height;
         cursor_y = point_scale.round_to_pixel(cursor_y);
     }
 

crates/epaint/src/text/text_layout_types.rs

@@ -232,6 +232,15 @@ pub struct TextFormat {
     /// Default: 0.0. Round to whole _pixels_ for crisp text.
     pub extra_letter_spacing: f32,
 
+    /// Explicit line height of the text in points.
+    ///
+    /// This is the distance between the bottom row of two subsequent lines of text.
+    ///
+    /// If `None` (the default), the line height is determined by the font.
+    ///
+    /// Round to whole _pixels_ for crisp text.
+    pub line_height: Option<f32>,
+
     /// Text color
     pub color: Color32,
 
@@ -249,12 +258,30 @@ pub struct TextFormat {
     // TODO(emilk): lowered
 }
 
+impl Default for TextFormat {
+    #[inline]
+    fn default() -> Self {
+        Self {
+            font_id: FontId::default(),
+            extra_letter_spacing: 0.0,
+            line_height: None,
+            color: Color32::GRAY,
+            background: Color32::TRANSPARENT,
+            italics: false,
+            underline: Stroke::NONE,
+            strikethrough: Stroke::NONE,
+            valign: Align::BOTTOM,
+        }
+    }
+}
+
 impl std::hash::Hash for TextFormat {
     #[inline]
     fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
         let Self {
             font_id,
             extra_letter_spacing,
+            line_height,
             color,
             background,
             italics,
@@ -264,6 +291,9 @@ impl std::hash::Hash for TextFormat {
         } = self;
         font_id.hash(state);
         crate::f32_hash(state, *extra_letter_spacing);
+        if let Some(line_height) = *line_height {
+            crate::f32_hash(state, line_height);
+        }
         color.hash(state);
         background.hash(state);
         italics.hash(state);
@@ -273,22 +303,6 @@ impl std::hash::Hash for TextFormat {
     }
 }
 
-impl Default for TextFormat {
-    #[inline]
-    fn default() -> Self {
-        Self {
-            font_id: FontId::default(),
-            color: Color32::GRAY,
-            background: Color32::TRANSPARENT,
-            italics: false,
-            underline: Stroke::NONE,
-            strikethrough: Stroke::NONE,
-            valign: Align::BOTTOM,
-            extra_letter_spacing: 0.0,
-        }
-    }
-}
-
 impl TextFormat {
     #[inline]
     pub fn simple(font_id: FontId, color: Color32) -> Self {
@@ -517,10 +531,12 @@ pub struct Glyph {
     /// `ascent` value from the font
     pub ascent: f32,
 
-    /// Advance width and font row height.
+    /// Advance width and line height.
+    ///
+    /// Does not control the visual size of the glyph (see [`Self::uv_rect`] for that).
     pub size: Vec2,
 
-    /// Position of the glyph in the font texture, in texels.
+    /// Position and size of the glyph in the font texture, in texels.
     pub uv_rect: UvRect,
 
     /// Index into [`LayoutJob::sections`]. Decides color etc.