Add extra_text_line_spacing to control vertical spacing between text lines (#8040)

Add `extra_text_line_spacing` to control vertical spacing between text
lines

**Description**
This PR adds a new `Spacing::extra_text_line_spacing` field to control
additional vertical spacing between lines of text.

The spacing is applied to text layout by adjusting
`TextFormat::line_height` based on the font row height plus the
configured extra spacing.

This improves text readability and allows consistent line spacing
customization for widgets such as `TextEdit` and `Label`.

---------

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

crates/egui/src/style.rs

@@ -419,6 +419,9 @@ pub struct Spacing {
     /// Default width of a [`crate::TextEdit`].
     pub text_edit_width: f32,
 
+    /// Additional vertical spacing between lines of text.
+    pub extra_text_line_spacing: f32,
+
     /// Checkboxes, radio button and collapsing headers have an icon at the start.
     /// This is the width/height of the outer part of this icon (e.g. the BOX of the checkbox).
     pub icon_width: f32,
@@ -1458,6 +1461,7 @@ impl Default for Spacing {
             slider_rail_height: 8.0,
             combo_width: 100.0,
             text_edit_width: 280.0,
+            extra_text_line_spacing: 0.0,
             icon_width: 14.0,
             icon_width_inner: 8.0,
             icon_spacing: 4.0,
@@ -1948,6 +1952,7 @@ impl Spacing {
             slider_rail_height,
             combo_width,
             text_edit_width,
+            extra_text_line_spacing,
             icon_width,
             icon_width_inner,
             icon_spacing,
@@ -2014,6 +2019,10 @@ impl Spacing {
                 ui.add(DragValue::new(text_edit_width).range(0.0..=1000.0));
                 ui.end_row();
 
+                ui.label("Extra text line spacing");
+                ui.add(DragValue::new(extra_text_line_spacing).range(0.0..=20.0));
+                ui.end_row();
+
                 ui.label("Tooltip wrap width");
                 ui.add(DragValue::new(tooltip_width).range(0.0..=1000.0));
                 ui.end_row();

crates/egui/src/widget_text.rs

@@ -769,14 +769,19 @@ impl WidgetText {
                     .visuals
                     .override_text_color
                     .unwrap_or(crate::Color32::PLACEHOLDER);
+
+                // We want the style overrides to take precedence over the fallback font
+                let font_id = FontSelection::default().resolve_with_fallback(style, fallback_font);
+                let line_height = ctx
+                    .fonts_mut(|f| f.row_height(&font_id) + style.spacing.extra_text_line_spacing);
+
                 let mut layout_job = LayoutJob::simple_format(
                     text,
                     TextFormat {
-                        // We want the style overrides to take precedence over the fallback font
+                        font_id,
-                        font_id: FontSelection::default()
-                            .resolve_with_fallback(style, fallback_font),
                         color,
                         valign: default_valign,
+                        line_height: Some(line_height),
                         ..Default::default()
                     },
                 );

crates/egui/src/widgets/text_edit/builder.rs

@@ -471,6 +471,8 @@ impl TextEdit<'_> {
 
         let font_id = font_selection.resolve(ui.style());
         let row_height = ui.fonts_mut(|f| f.row_height(&font_id));
+        let line_height = row_height + ui.spacing().extra_text_line_spacing;
+
         const MIN_WIDTH: f32 = 24.0; // Never make a [`TextEdit`] more narrow than this.
         let available_width = ui.available_width().at_least(MIN_WIDTH);
         let desired_width = desired_width
@@ -489,12 +491,17 @@ impl TextEdit<'_> {
             layout_job.halign = align.x();
             // We want to keep the trailing whitespace, since hiding it feels really weird when typing
             layout_job.keep_trailing_whitespace = true;
+
+            for section in &mut layout_job.sections {
+                section.format.line_height = Some(line_height);
+            }
+
             ui.fonts_mut(|f| f.layout_job(layout_job))
         };
 
         let layouter = layouter.unwrap_or(&mut default_layouter);
 
-        let min_inner_height = (desired_height_rows.at_least(1) as f32) * row_height;
+        let min_inner_height = (desired_height_rows.at_least(1) as f32) * line_height;
 
         let id = id.unwrap_or_else(|| {
             if let Some(id_salt) = id_salt {