Change text color of selected text (#7691)

Selected text now gets the color of `visuals.selection.stroke.color`.
This means you can have inverted colors for selected text, like in the
new test:
<img width="154" height="46" alt="image"
src="https://github.com/user-attachments/assets/2666361d-d7e2-4d50-8e4d-2fcc128f1a81"
/>


It also means the color of selected text in labels matches that of the
text color of selected buttons.

crates/egui/src/style.rs

@@ -1129,7 +1129,10 @@ impl Visuals {
 #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
 #[cfg_attr(feature = "serde", serde(default))]
 pub struct Selection {
+    /// Background color behind selected text and other selectable buttons.
     pub bg_fill: Color32,
+
+    /// Color of selected text.
     pub stroke: Stroke,
 }
 

crates/egui/src/text_selection/visuals.rs

@@ -25,7 +25,9 @@ pub fn paint_text_selection(
     // and so we need to clone it if it is shared:
     let galley: &mut Galley = Arc::make_mut(galley);
 
-    let color = visuals.selection.bg_fill;
+    let background_color = visuals.selection.bg_fill;
+    let text_color = visuals.selection.stroke.color;
+
     let [min, max] = cursor_range.sorted_cursors();
     let min = galley.layout_from_cursor(min);
     let max = galley.layout_from_cursor(max);
@@ -53,6 +55,31 @@ pub fn paint_text_selection(
         let rect = Rect::from_min_max(pos2(left, 0.0), pos2(right, row.size.y));
         let mesh = &mut row.visuals.mesh;
 
+        if !row.glyphs.is_empty() {
+            // Change color of the selected text:
+            let first_glyph_index = if ri == min.row { min.column } else { 0 };
+            let last_glyph_index = if ri == max.row {
+                max.column
+            } else {
+                row.glyphs.len() - 1
+            };
+
+            let first_vertex_index = row
+                .glyphs
+                .get(first_glyph_index)
+                .map_or(row.visuals.glyph_vertex_range.start, |g| {
+                    g.first_vertex as _
+                });
+            let last_vertex_index = row
+                .glyphs
+                .get(last_glyph_index)
+                .map_or(row.visuals.glyph_vertex_range.end, |g| g.first_vertex as _);
+
+            for vi in first_vertex_index..last_vertex_index {
+                mesh.vertices[vi].color = text_color;
+            }
+        }
+
         // Time to insert the selection rectangle into the row mesh.
         // It should be on top (after) of any background in the galley,
         // but behind (before) any glyphs. The row visuals has this information:
@@ -60,7 +87,7 @@ pub fn paint_text_selection(
 
         // Start by appending the selection rectangle to end of the mesh, as two triangles (= 6 indices):
         let num_indices_before = mesh.indices.len();
-        mesh.add_colored_rect(rect, color);
+        mesh.add_colored_rect(rect, background_color);
         assert_eq!(
             num_indices_before + 6,
             mesh.indices.len(),