[parley] new selection logic and an editor example

parley/src/layout/cursor.rs

@@ -155,6 +155,44 @@ impl Cursor {
  pub fn is_trailing(&self) -> bool {
  self.text_end == self.insert_point
  }
+
+ /// Given the layout that generated this cursor, return a new cursor
+ /// for the corresponding position on the next line.
+ ///
+ /// If `h_pos` is provided, then it will be used as the horizontal offset
+ /// for computing the position on the next line.
+ ///
+ /// Returns `None` if the cursor should remain in its current position.
+ pub fn next_line<B: Brush>(&self, layout: &Layout<B>, h_pos: Option<f32>) -> Option<Cursor> {
+ move_to_line(layout, self, h_pos, self.path.line_index.checked_add(1)?)
+ }
+
+ /// Given the layout that generated this cursor, return a new cursor
+ /// for the corresponding position on the previous line.
+ ///
+ /// If `h_pos` is provided, then it will be used as the horizontal offset
+ /// for computing the position on the previous line.
+ ///
+ /// Returns `None` if the cursor should remain in its current position.
+ pub fn prev_line<B: Brush>(&self, layout: &Layout<B>, h_pos: Option<f32>) -> Option<Cursor> {
+ move_to_line(layout, self, h_pos, self.path.line_index.checked_sub(1)?)
+ }
+}
+
+fn move_to_line<B: Brush>(
+ layout: &Layout<B>,
+ cursor: &Cursor,
+ h_pos: Option<f32>,
+ line_index: usize,
+) -> Option<Cursor> {
+ let line = layout.get(line_index)?;
+ let metrics = line.metrics();
+ let y = metrics.baseline - metrics.line_height * 0.5;
+ Some(Cursor::from_point(
+ layout,
+ h_pos.unwrap_or(cursor.offset),
+ y,
+ ))
 }
 
 /// Index based path to a cluster.