input: Ensure resizing the window doesn't force the cursor back into …

…view (#370)

Fix #331

It is ensured that the scroll offset remains consistent during parent
container resizing, preventing the cursor from being forced back into
view unless the user interacts with the input, providing a more
consistent user experience in scenarios where automatic scrolling during
resizing is undesirable.

This behavior aligns with common text editors and input fields where
resizing the window doesn't force the cursor back into view.

![2024-10-21 20 27
00](https://github.com/user-attachments/assets/599ef72d-3ec8-4fe5-a26c-10263044db6f)

crates/ui/src/input/input.rs

@@ -131,6 +131,8 @@ pub struct TextInput {
     marked_range: Option<Range<usize>>,
     last_layout: Option<ShapedLine>,
     last_bounds: Option<Bounds<Pixels>>,
+    last_cursor_offset: Option<usize>,
+    last_selected_range: Option<Range<usize>>,
     scroll_offset: Point<Pixels>,
     is_selecting: bool,
     disabled: bool,
@@ -160,6 +162,8 @@ impl TextInput {
             marked_range: None,
             last_layout: None,
             last_bounds: None,
+            last_cursor_offset: None,
+            last_selected_range: None,
             scroll_offset: point(px(0.), px(0.)),
             is_selecting: false,
             disabled: false,
@@ -975,26 +979,30 @@ impl Element for TextElement {
         let cursor_pos = line.x_for_index(cursor);
         let cursor_start = line.x_for_index(selected_range.start);
         let cursor_end = line.x_for_index(selected_range.end);
-
-        scroll_offset.x = if scroll_offset.x + cursor_pos > (bounds.size.width - right_margin) {
-            // cursor is out of right
-            bounds.size.width - right_margin - cursor_pos
-        } else if scroll_offset.x + cursor_pos < px(0.) {
-            // cursor is out of left
-            scroll_offset.x - cursor_pos
-        } else {
-            scroll_offset.x
-        };
-
-        if input.selection_reversed {
-            if scroll_offset.x + cursor_start < px(0.) {
-                // selection start is out of left
-                scroll_offset.x = -cursor_start;
-            }
-        } else {
-            if scroll_offset.x + cursor_end <= px(0.) {
-                // selection end is out of left
-                scroll_offset.x = -cursor_end;
+        let cursor_moved = input.last_cursor_offset != Some(cursor);
+        let selection_changed = input.last_selected_range != Some(selected_range.clone());
+
+        if cursor_moved || selection_changed {
+            scroll_offset.x = if scroll_offset.x + cursor_pos > (bounds.size.width - right_margin) {
+                // cursor is out of right
+                bounds.size.width - right_margin - cursor_pos
+            } else if scroll_offset.x + cursor_pos < px(0.) {
+                // cursor is out of left
+                scroll_offset.x - cursor_pos
+            } else {
+                scroll_offset.x
+            };
+
+            if input.selection_reversed {
+                if scroll_offset.x + cursor_start < px(0.) {
+                    // selection start is out of left
+                    scroll_offset.x = -cursor_start;
+                }
+            } else {
+                if scroll_offset.x + cursor_end <= px(0.) {
+                    // selection end is out of left
+                    scroll_offset.x = -cursor_end;
+                }
             }
         }
 
@@ -1053,6 +1061,8 @@ impl Element for TextElement {
         let focus_handle = self.input.read(cx).focus_handle.clone();
         let focused = focus_handle.is_focused(cx);
         let bounds = prepaint.bounds;
+        let selected_range = self.input.read(cx).selected_range.clone();
+        let cursor = self.input.read(cx).cursor_offset();
 
         cx.handle_input(
             &focus_handle,
@@ -1073,6 +1083,8 @@ impl Element for TextElement {
             input.scroll_offset = prepaint.scroll_offset;
             input.last_layout = Some(line);
             input.last_bounds = Some(bounds);
+            input.last_cursor_offset = Some(cursor);
+            input.last_selected_range = Some(selected_range);
         });
 
         self.paint_mouse_listeners(cx);