Make text cursor always appear on click (#5420)

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### Problem
When clicking on a TextEdit sometimes the cursor doesn't appear
immediately which makes it feel like the click was not registered for a
second. This is because the start time for the blinking animation is
only reset on keyboard input, but not on mouse interaction.

It's hard to tell on the video but the cursor doesn't show immediately
after clicking if the blink timer happens to be off.


https://github.com/user-attachments/assets/9f049bd0-0375-4291-b2ef-697777fb854d


### Solution
Reset the click timer every time a `TextEdit` is clicked. 

Additionally, the cursor is now correctly painted on the pixel boundary.
IMO we should default to 1px cursor (instead of 2px) but that's not
included in this PR. Happy to make that change too.


https://github.com/user-attachments/assets/6c489414-f2c4-4dc6-85dd-f8bc457edad0

crates/egui/src/text_selection/visuals.rs

@@ -96,8 +96,19 @@ pub fn paint_text_selection(
 pub fn paint_cursor_end(painter: &Painter, visuals: &Visuals, cursor_rect: Rect) {
     let stroke = visuals.text_cursor.stroke;
 
-    let top = cursor_rect.center_top();
-    let bottom = cursor_rect.center_bottom();
+    // Ensure the cursor is aligned to the pixel grid for whole number widths.
+    // See https://github.com/emilk/egui/issues/5164
+    let (top, bottom) = if (stroke.width as usize) % 2 == 0 {
+        (
+            painter.round_pos_to_pixels(cursor_rect.center_top()),
+            painter.round_pos_to_pixels(cursor_rect.center_bottom()),
+        )
+    } else {
+        (
+            painter.round_pos_to_pixel_center(cursor_rect.center_top()),
+            painter.round_pos_to_pixel_center(cursor_rect.center_bottom()),
+        )
+    };
 
     painter.line_segment([top, bottom], (stroke.width, stroke.color));
 
@@ -121,14 +132,14 @@ pub fn paint_text_cursor(
     ui: &Ui,
     painter: &Painter,
     primary_cursor_rect: Rect,
-    time_since_last_edit: f64,
+    time_since_last_interaction: f64,
 ) {
     if ui.visuals().text_cursor.blink {
         let on_duration = ui.visuals().text_cursor.on_duration;
         let off_duration = ui.visuals().text_cursor.off_duration;
         let total_duration = on_duration + off_duration;
 
-        let time_in_cycle = (time_since_last_edit % (total_duration as f64)) as f32;
+        let time_in_cycle = (time_since_last_interaction % (total_duration as f64)) as f32;
 
         let wake_in = if time_in_cycle < on_duration {
             // Cursor is visible

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

@@ -603,6 +603,8 @@ impl<'t> TextEdit<'t> {
 
                 if did_interact || response.clicked() {
                     ui.memory_mut(|mem| mem.request_focus(response.id));
+
+                    state.last_interaction_time = ui.ctx().input(|i| i.time);
                 }
             }
         }
@@ -746,7 +748,7 @@ impl<'t> TextEdit<'t> {
                     if text.is_mutable() && interactive {
                         let now = ui.ctx().input(|i| i.time);
                         if response.changed || selection_changed {
-                            state.last_edit_time = now;
+                            state.last_interaction_time = now;
                         }
 
                         // Only show (and blink) cursor if the egui viewport has focus.
@@ -759,7 +761,7 @@ impl<'t> TextEdit<'t> {
                                 ui,
                                 &painter,
                                 primary_cursor_rect,
-                                now - state.last_edit_time,
+                                now - state.last_interaction_time,
                             );
                         }
 

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

@@ -53,10 +53,10 @@ pub struct TextEditState {
     #[cfg_attr(feature = "serde", serde(skip))]
     pub(crate) singleline_offset: f32,
 
-    /// When did the user last press a key?
+    /// When did the user last press a key or click on the `TextEdit`.
     /// Used to pause the cursor animation when typing.
     #[cfg_attr(feature = "serde", serde(skip))]
-    pub(crate) last_edit_time: f64,
+    pub(crate) last_interaction_time: f64,
 }
 
 impl TextEditState {