Scroll so that text cursor remains visible

Closes #165

egui/src/containers/scroll_area.rs

@@ -498,7 +498,7 @@ impl Prepared {
                     let clip_end = clip_rect.max[d];
                     let mut spacing = ui.spacing().item_spacing[d];
 
-                    if let Some(align) = align {
+                    let delta = if let Some(align) = align {
                         let center_factor = align.to_factor();
 
                         let offset =
@@ -507,19 +507,20 @@ impl Prepared {
                         // Depending on the alignment we need to add or subtract the spacing
                         spacing *= remap(center_factor, 0.0..=1.0, -1.0..=1.0);
 
-                        state.offset[d] = offset + spacing;
+                        offset + spacing
                     } else if start < clip_start && end < clip_end {
-                        let min_adjust =
-                            (clip_start - start + spacing).min(clip_end - end - spacing);
-                        state.offset[d] -= min_adjust;
+                        -(clip_start - start + spacing).min(clip_end - end - spacing)
                     } else if end > clip_end && start > clip_start {
-                        let min_adjust =
-                            (end - clip_end + spacing).min(start - clip_start - spacing);
-                        state.offset[d] += min_adjust;
+                        (end - clip_end + spacing).min(start - clip_start - spacing)
                     } else {
                         // Ui is already in view, no need to adjust scroll.
-                        continue;
+                        0.0
                     };
+
+                    if delta != 0.0 {
+                        state.offset[d] += delta;
+                        ui.ctx().request_repaint();
+                    }
                 }
             }
         }

egui/src/response.rs

@@ -443,10 +443,11 @@ impl Response {
         )
     }
 
-    /// Adjust the scroll position until this UI becomes visible. If `align` is not provided, it'll scroll enough to
-    /// bring the UI into view.
+    /// Adjust the scroll position until this UI becomes visible.
     ///
-    /// See also [`Ui::scroll_to_cursor`]
+    /// If `align` is `None`, it'll scroll enough to bring the UI into view.
+    ///
+    /// See also: [`Ui::scroll_to_cursor`], [`Ui::scroll_to`].
     ///
     /// ```
     /// # egui::__run_test_ui(|ui| {

egui/src/ui.rs

@@ -889,10 +889,36 @@ impl Ui {
         (response, painter)
     }
 
-    /// Adjust the scroll position until the cursor becomes visible. If `align` is not provided, it'll scroll enough to
-    /// bring the cursor into view.
+    /// Adjust the scroll position of any parent [`ScrollArea`] so that the given `Rect` becomes visible.
     ///
-    /// See also [`Response::scroll_to_me`]
+    /// If `align` is `None`, it'll scroll enough to bring the cursor into view.
+    ///
+    /// See also: [`Response::scroll_to_me`], [`Ui::scroll_to`].
+    ///
+    /// ```
+    /// # use egui::Align;
+    /// # egui::__run_test_ui(|ui| {
+    /// egui::ScrollArea::vertical().show(ui, |ui| {
+    ///     // …
+    ///     let response = ui.button("Center on me.").clicked();
+    ///     if response.clicked() {
+    ///         ui.scroll_to_rect(response.rect, Some(Align::CENTER));
+    ///     }
+    /// });
+    /// # });
+    /// ```
+    pub fn scroll_to_rect(&self, rect: Rect, align: Option<Align>) {
+        for d in 0..2 {
+            let range = rect.min[d]..=rect.max[d];
+            self.ctx().frame_state().scroll_target[d] = Some((range, align));
+        }
+    }
+
+    /// Adjust the scroll position of any parent [`ScrollArea`] so that the cursor (where the next widget goes) becomes visible.
+    ///
+    /// If `align` is not provided, it'll scroll enough to bring the cursor into view.
+    ///
+    /// See also: [`Response::scroll_to_me`], [`Ui::scroll_to`].
     ///
     /// ```
     /// # use egui::Align;
@@ -909,7 +935,7 @@ impl Ui {
     /// });
     /// # });
     /// ```
-    pub fn scroll_to_cursor(&mut self, align: Option<Align>) {
+    pub fn scroll_to_cursor(&self, align: Option<Align>) {
         let target = self.next_widget_position();
         for d in 0..2 {
             let target = target[d];

egui/src/widgets/text_edit/builder.rs

@@ -561,7 +561,7 @@ impl<'t> TextEdit<'t> {
                     // We paint the cursor on top of the text, in case
                     // the text galley has backgrounds (as e.g. `code` snippets in markup do).
                     paint_cursor_selection(ui, &painter, text_draw_pos, &galley, &cursor_range);
-                    paint_cursor_end(
+                    let cursor_pos = paint_cursor_end(
                         ui,
                         row_height,
                         &painter,
@@ -570,6 +570,8 @@ impl<'t> TextEdit<'t> {
                         &cursor_range.primary,
                     );
 
+                    ui.scroll_to_rect(cursor_pos, None); // keep cursor in view
+
                     if interactive && text.is_mutable() {
                         // egui_web uses `text_cursor_pos` when showing IME,
                         // so only set it when text is editable and visible!
@@ -887,7 +889,7 @@ fn paint_cursor_end(
     pos: Pos2,
     galley: &Galley,
     cursor: &Cursor,
-) {
+) -> Rect {
     let stroke = ui.visuals().selection.stroke;
 
     let mut cursor_pos = galley.pos_from_cursor(cursor).translate(pos.to_vec2());
@@ -915,6 +917,8 @@ fn paint_cursor_end(
             (width, stroke.color),
         );
     }
+
+    cursor_pos
 }
 
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