editor: typewriter room as rows, so drawing and text queries share one origin; a placement resets centering

src/editor/ime.rs

@@ -104,7 +104,7 @@ impl CodeEditor {
         to_utf16(text, range.start)..to_utf16(text, range.end)
     }
 
-    fn byte_range(&self, range: &Range<usize>) -> Range<usize> {
+    pub(crate) fn byte_range(&self, range: &Range<usize>) -> Range<usize> {
         let text = self.buffer.text();
         from_utf16(text, range.start)..from_utf16(text, range.end)
     }

src/editor/layout.rs

@@ -19,6 +19,8 @@ pub(crate) enum Row {
     Ghost(usize),
     /// The inline chat's rows; the first draws it.
     Chat(usize),
+    /// Typewriter room past an end.
+    Room,
 }
 
 /// Which lines folds hide.

src/editor/moves.rs

@@ -158,6 +158,7 @@ impl CodeEditor {
             .iter()
             .rposition(|row| matches!(row, Row::Line(shown) if *shown <= line))
             .unwrap_or(0)
+            + self.pad
     }
 
     /// Scrolls the primary cursor into view: from below when moving down, from above when moving up.

src/editor/row.rs

@@ -23,6 +23,10 @@ impl CodeEditor {
             .h(self.frame.line)
             .flex();
         let caret = self.buffer.line_of(self.primary().head);
+        let base = match self.frame.rows[ix] {
+            Row::Line(line) => base.debug_selector(move || format!("editor-line-{line}")),
+            _ => base,
+        };
         match self.frame.rows[ix] {
             Row::Line(line) if self.options.focus_line && line != caret => {
                 self.line_row(base.opacity(FADED), ix, line, window, cx)
@@ -32,6 +36,7 @@ impl CodeEditor {
             Row::Removed(hunk, at) => self.removed_row(base, ix, hunk, at, cx),
             Row::Ghost(at) => self.ghost_row(base, ix, at, cx),
             Row::Chat(at) => self.chat_row(base, ix, at, cx),
+            Row::Room => base.into_any_element(),
         }
     }
 

src/editor/state.rs

@@ -100,7 +100,7 @@ pub(crate) struct Metrics {
     pub top: Pixels,
     pub advance: Pixels,
     pub line: Pixels,
-    /// The view's height, under any typewriter room.
+    /// The view's height.
     pub height: Pixels,
 }
 
@@ -124,8 +124,8 @@ pub struct CodeEditor {
     pub(crate) metrics: Metrics,
     /// The caret row typewriter scrolling last centered.
     pub(crate) centered: Option<usize>,
-    /// Typewriter room past each end, as last drawn.
-    pub(crate) room: Pixels,
+    /// Typewriter room rows at each end.
+    pub(crate) pad: usize,
     pub(crate) dragging: bool,
     pub(crate) caret_on: bool,
     /// Blink runs only while focused, or unseen cursors redraw forever.
@@ -212,7 +212,7 @@ impl CodeEditor {
             composing: None,
             metrics: Metrics::default(),
             centered: None,
-            room: Pixels::ZERO,
+            pad: 0,
             dragging: false,
             caret_on: true,
             focused: false,

src/editor/view.rs

@@ -54,8 +54,7 @@ impl CodeEditor {
 
     /// The first line the list shows, after scrolling.
     pub(crate) fn top_line(&self) -> Option<usize> {
-        // Typewriter room above the first line is no line.
-        let scrolled = -self.scroll.0.borrow().base_handle.offset().y - self.room;
+        let scrolled = -self.scroll.0.borrow().base_handle.offset().y;
         let first = (scrolled / self.frame.line).floor().max(0.0) as usize;
         self.frame.rows[first.min(self.frame.rows.len().saturating_sub(1))..]
             .iter()
@@ -252,8 +251,16 @@ impl Render for CodeEditor {
             _ => Vec::new(),
         };
         let minimap = self.frame.minimap;
+        // Half a view of room rows: the ends center too.
+        self.pad = match self.options.typewriter && line > Pixels::ZERO {
+            true => (self.metrics.height / 2.0 / line).ceil() as usize,
+            false => 0,
+        };
+        let mut shown = vec![Row::Room; self.pad];
+        shown.extend(rows(&self.buffer, &hide, &self.marks));
+        shown.extend(std::iter::repeat_n(Row::Room, self.pad));
         self.frame = Frame {
-            rows: rows(&self.buffer, &hide, &self.marks),
+            rows: shown,
             folds: found,
             brackets: found_brackets,
             advance,
@@ -271,13 +278,6 @@ impl Render for CodeEditor {
                 .scroll_to_item_strict(row, ScrollStrategy::Center);
             self.centered = Some(row);
         }
-        // Half a view of room: a resize keeps the center.
-        let height = self.metrics.height;
-        self.room = match self.options.typewriter {
-            true => height / 2.0,
-            false => gpui::px(0.0),
-        };
-        let room = self.room;
         let sticky = if self.options.sticky {
             self.sticky(cx)
         } else {
@@ -292,9 +292,7 @@ impl Render for CodeEditor {
             }),
         )
         .track_scroll(&self.scroll)
-        .size_full()
-        .pt(room)
-        .pb(room);
+        .size_full();
         let (top, focus, input) = (cx.entity(), self.focus.clone(), cx.entity());
         let unlock = cx.entity();
         let banner = self.options.read_only.then(|| {