map editor scroll

kiln-tui/src/editor.rs

@@ -300,7 +300,7 @@ impl EditorState {
     /// board (right-click handling). No-op when the click is off the board. When draw
     /// mode is on and the cursor lands on a new cell, stamps the current thing there.
     pub(crate) fn set_cursor_at_screen(&mut self, sx: u16, sy: u16) {
-        let cell = screen_to_board(self.last_board_area, &self.board(), sx, sy);
+        let cell = screen_to_board(self.last_board_area, &self.board(), sx, sy, self.cursor);
         if let Some((bx, by)) = cell {
             let target = (bx as i32, by as i32);
             let moved = target != self.cursor;
@@ -417,12 +417,12 @@ pub(crate) fn draw_editor(frame: &mut Frame, ed: &mut EditorState, ui: &mut Ui)
             }
             let inner = block.inner(board_area);
             frame.render_widget(block, board_area);
-            frame.render_widget(BoardWidget::new(&board), inner);
+            frame.render_widget(BoardWidget::new(&board).with_focus(ed.cursor.0, ed.cursor.1), inner);
 
             // Overlay the cursor during its visible phase (a light-gray solid block).
             if ed.blink_on {
                 let (cx, cy) = (ed.cursor.0 as usize, ed.cursor.1 as usize);
-                if let Some((sx, sy)) = board_to_screen(inner, &board, cx, cy)
+                if let Some((sx, sy)) = board_to_screen(inner, &board, cx, cy, (ed.cursor.0, ed.cursor.1))
                     && let Some(cell) = frame.buffer_mut().cell_mut((sx, sy))
                 {
                     cell.set_char(CURSOR_CHAR)

kiln-tui/src/render.rs

@@ -13,16 +13,27 @@ use ratatui::layout::Rect;
 use ratatui::widgets::Widget;
 
 /// A ratatui widget that draws a [`Board`] (with objects and the player) into a
-/// rectangular area, scrolled so the player stays visible on larger boards.
+/// rectangular area, scrolled so a chosen focus cell stays visible on larger boards.
 pub struct BoardWidget<'a> {
     /// The board to render. Borrowed for the duration of the draw.
     pub board: &'a Board,
+    /// The board cell (x, y) the viewport scrolls to keep visible. Defaults to
+    /// the player position so play mode requires no extra setup.
+    focus: (i32, i32),
 }
 
 impl<'a> BoardWidget<'a> {
-    /// Creates a widget that renders `board`.
+    /// Creates a widget that renders `board`, scrolling to follow the player.
     pub fn new(board: &'a Board) -> Self {
-        Self { board }
+        let focus = (board.player.x, board.player.y);
+        Self { board, focus }
+    }
+
+    /// Overrides the scroll focus to `(x, y)` — use in the editor to follow the
+    /// cursor instead of the player.
+    pub fn with_focus(mut self, x: i32, y: i32) -> Self {
+        self.focus = (x, y);
+        self
     }
 
     /// Lays out one axis of the board within a viewport `view` cells long.
@@ -51,17 +62,25 @@ impl<'a> BoardWidget<'a> {
 }
 
 /// Maps a board cell `(bx, by)` to its screen position within `area`, using the
-/// same centering/scrolling layout as [`BoardWidget`]. Returns `None` when the
-/// cell is scrolled out of view.
+/// same centering/scrolling layout as [`BoardWidget`] with the given `focus`.
+/// Returns `None` when the cell is scrolled out of view.
+///
+/// Pass `(board.player.x, board.player.y)` as `focus` in play mode, or the
+/// editor cursor coordinates in editor mode, to match the active viewport.
 ///
 /// The inverse of [`screen_to_board`]; both reuse [`BoardWidget::axis`] so they
 /// stay consistent with how the board is actually drawn. (Unlike
 /// `speech::board_screen_pos`, which clamps off-screen cells to the edge, this
 /// reports off-screen cells as `None` — needed for exact cursor placement.)
-pub fn board_to_screen(area: Rect, board: &Board, bx: usize, by: usize) -> Option<(u16, u16)> {
-    let (off_x, pad_x, cols) = BoardWidget::axis(board.width, area.width as usize, board.player.x);
-    let (off_y, pad_y, rows) =
-        BoardWidget::axis(board.height, area.height as usize, board.player.y);
+pub fn board_to_screen(
+    area: Rect,
+    board: &Board,
+    bx: usize,
+    by: usize,
+    focus: (i32, i32),
+) -> Option<(u16, u16)> {
+    let (off_x, pad_x, cols) = BoardWidget::axis(board.width, area.width as usize, focus.0);
+    let (off_y, pad_y, rows) = BoardWidget::axis(board.height, area.height as usize, focus.1);
     // Cell must fall within the visible window on both axes.
     if bx < off_x || bx >= off_x + cols || by < off_y || by >= off_y + rows {
         return None;
@@ -72,12 +91,19 @@ pub fn board_to_screen(area: Rect, board: &Board, bx: usize, by: usize) -> Optio
 }
 
 /// Maps a screen position `(sx, sy)` to the board cell drawn there within `area`,
-/// the inverse of [`board_to_screen`]. Returns `None` when the point lies outside
-/// the drawn board (in the centering pad or past the visible cells).
-pub fn screen_to_board(area: Rect, board: &Board, sx: u16, sy: u16) -> Option<(usize, usize)> {
-    let (off_x, pad_x, cols) = BoardWidget::axis(board.width, area.width as usize, board.player.x);
-    let (off_y, pad_y, rows) =
-        BoardWidget::axis(board.height, area.height as usize, board.player.y);
+/// the inverse of [`board_to_screen`]. `focus` must match the focus used when
+/// the board was rendered so the coordinate mapping is consistent.
+/// Returns `None` when the point lies outside the drawn board (in the centering
+/// pad or past the visible cells).
+pub fn screen_to_board(
+    area: Rect,
+    board: &Board,
+    sx: u16,
+    sy: u16,
+    focus: (i32, i32),
+) -> Option<(usize, usize)> {
+    let (off_x, pad_x, cols) = BoardWidget::axis(board.width, area.width as usize, focus.0);
+    let (off_y, pad_y, rows) = BoardWidget::axis(board.height, area.height as usize, focus.1);
     // Screen-space offset from the first drawn cell; reject anything before it.
     let col = (sx as i32) - (area.x as i32 + pad_x as i32);
     let row = (sy as i32) - (area.y as i32 + pad_y as i32);
@@ -118,9 +144,9 @@ impl Widget for BoardWidget<'_> {
     fn render(self, area: Rect, buf: &mut Buffer) {
         let board = self.board;
         // Resolve each axis independently: a small board is centered, a large
-        // one scrolls to keep the player on screen.
-        let (off_x, pad_x, cols) = Self::axis(board.width, area.width as usize, board.player.x);
-        let (off_y, pad_y, rows) = Self::axis(board.height, area.height as usize, board.player.y);
+        // one scrolls to keep the focus cell on screen.
+        let (off_x, pad_x, cols) = Self::axis(board.width, area.width as usize, self.focus.0);
+        let (off_y, pad_y, rows) = Self::axis(board.height, area.height as usize, self.focus.1);
 
         // Walk the visible board cells, placing each after the centering pad.
         for row in 0..rows {