Three-zone drop system: squeeze, split, center

Zone layout (outer to inner per edge):
  0–1/6    squeeze (amber): insert dropped tile between two existing tiles
  1/6–1/3  split (blue):    bisect the target tile 50/50
  1/3–2/3  center (green):  swap/move

Squeeze behaviour: find the tile adjacent to the target in the drop
direction; insert dragged tile to the opposite side of that neighbor
so it lands visually between them. Falls back to split when no neighbor
exists (edge tile).

- _zone_at: returns "squeeze_*"/"split_*"/"center" with dominant-axis
  selection (nearest edge wins)
- _adjacent_tile: finds geometrically adjacent tile by pixel proximity
- _do_drop: routes squeeze→insert-at-neighbor, split→bisect, center→swap
- paintEvent: amber/blue/green per zone type

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 128 insertions, 23 deletions

diff --git a/ui/windows/plot_window.py b/ui/windows/plot_window.py
index 615b7ca..15d509b 100644
--- a/ui/windows/plot_window.py
+++ b/ui/windows/plot_window.py
@@ -460,14 +460,25 @@ _LC_HEIGHT   = 160  # fixed canvas height
 
 
 def _zone_overlay_rect(r: QRect, zone: str) -> QRect:
-    if zone == "left":
+    # split_* → highlight half of tile
+    if zone == "split_left":
         return QRect(r.x(), r.y(), r.width() // 2, r.height())
-    if zone == "right":
+    if zone == "split_right":
         return QRect(r.x() + r.width() // 2, r.y(), r.width() - r.width() // 2, r.height())
-    if zone == "top":
+    if zone == "split_top":
         return QRect(r.x(), r.y(), r.width(), r.height() // 2)
-    if zone == "bottom":
+    if zone == "split_bottom":
         return QRect(r.x(), r.y() + r.height() // 2, r.width(), r.height() - r.height() // 2)
+    # squeeze_* → thin bar at the edge (insert-between indicator)
+    BAR = 10
+    if zone == "squeeze_left":
+        return QRect(r.x(), r.y(), BAR, r.height())
+    if zone == "squeeze_right":
+        return QRect(r.right() - BAR, r.y(), BAR, r.height())
+    if zone == "squeeze_top":
+        return QRect(r.x(), r.y(), r.width(), BAR)
+    if zone == "squeeze_bottom":
+        return QRect(r.x(), r.bottom() - BAR, r.width(), BAR)
     # center (move)
     return r
 
@@ -586,28 +597,81 @@ class LayoutCanvas(QFrame):
     # ── Drop zone detection ───────────────────────────────────────────────────
 
     def _zone_at(self, pos: QPoint) -> Optional[Tuple[int, str]]:
+        """
+        Returns (pane_idx, zone) where zone is one of:
+          squeeze_left/right/top/bottom  — outer 1/6, insert between tiles
+          split_left/right/top/bottom    — 1/6 to 1/3, bisect tile
+          center                         — inner 1/3, swap/move
+        """
         dragging_idx = self._drag_tile.pane_index if self._drag_tile else -1
         for pane_idx, rect in self._tile_rects.items():
             if pane_idx == dragging_idx:
                 continue
             if not rect.contains(pos):
                 continue
-            rel_x = pos.x() - rect.x()
-            rel_y = pos.y() - rect.y()
+            rx = pos.x() - rect.x()
+            ry = pos.y() - rect.y()
             w, h = rect.width(), rect.height()
-            zone_w = max(1, w // 3)
-            zone_h = max(1, h // 3)
-            if rel_x < zone_w:
-                return (pane_idx, "left")
-            if rel_x > w - zone_w:
-                return (pane_idx, "right")
-            if rel_y < zone_h:
-                return (pane_idx, "top")
-            if rel_y > h - zone_h:
-                return (pane_idx, "bottom")
-            return (pane_idx, "center")  # center — move/swap
+            sq_w = max(1, w // 6)
+            sp_w = max(1, w // 3)
+            sq_h = max(1, h // 6)
+            sp_h = max(1, h // 3)
+
+            # X-axis zone
+            if rx < sq_w:           x_zone = "squeeze_left"
+            elif rx < sp_w:         x_zone = "split_left"
+            elif rx > w - sq_w:     x_zone = "squeeze_right"
+            elif rx > w - sp_w:     x_zone = "split_right"
+            else:                   x_zone = "center"
+
+            # Y-axis zone
+            if ry < sq_h:           y_zone = "squeeze_top"
+            elif ry < sp_h:         y_zone = "split_top"
+            elif ry > h - sq_h:     y_zone = "squeeze_bottom"
+            elif ry > h - sp_h:     y_zone = "split_bottom"
+            else:                   y_zone = "center"
+
+            # Pick dominant axis (nearest edge wins; center loses to any edge)
+            if x_zone == "center" and y_zone == "center":
+                return (pane_idx, "center")
+            if x_zone == "center":
+                return (pane_idx, y_zone)
+            if y_zone == "center":
+                return (pane_idx, x_zone)
+            # Both non-center: whichever is closer to the edge
+            dx = min(rx, w - rx)
+            dy = min(ry, h - ry)
+            return (pane_idx, x_zone if dx <= dy else y_zone)
         return None
 
+    def _adjacent_tile(self, pane_idx: int, direction: str) -> Optional[int]:
+        """Find the tile immediately adjacent to pane_idx in the given direction."""
+        r = self._tile_rects.get(pane_idx)
+        if r is None:
+            return None
+        dragging_idx = self._drag_tile.pane_index if self._drag_tile else -1
+        tol = _LC_GAP + 3
+        best: Optional[int] = None
+        best_dist = float("inf")
+        for other_idx, other_r in self._tile_rects.items():
+            if other_idx in (pane_idx, dragging_idx):
+                continue
+            if direction == "left":
+                dist = r.left() - other_r.right()
+                overlap = min(r.bottom(), other_r.bottom()) - max(r.top(), other_r.top())
+            elif direction == "right":
+                dist = other_r.left() - r.right()
+                overlap = min(r.bottom(), other_r.bottom()) - max(r.top(), other_r.top())
+            elif direction == "top":
+                dist = r.top() - other_r.bottom()
+                overlap = min(r.right(), other_r.right()) - max(r.left(), other_r.left())
+            else:  # bottom
+                dist = other_r.top() - r.bottom()
+                overlap = min(r.right(), other_r.right()) - max(r.left(), other_r.left())
+            if 0 <= dist <= tol and overlap > 4 and dist < best_dist:
+                best, best_dist = other_idx, dist
+        return best
+
     # ── Drag ─────────────────────────────────────────────────────────────────
 
     def mousePressEvent(self, event) -> None:
@@ -651,14 +715,52 @@ class LayoutCanvas(QFrame):
         if dragged_idx == target_idx or self._tree is None:
             self._reposition_tiles()
             return
+
         if zone == "center":
             new_tree = _tree_swap(self._tree, dragged_idx, target_idx)
-        else:
-            new_tree = _tree_remove(self._tree, dragged_idx)
-            if new_tree is None:
+            self._tree = new_tree
+            if self._cfg_ref is not None:
+                self._cfg_ref.tree = new_tree
+            self._reposition_tiles()
+            self.arrangement_changed.emit()
+            return
+
+        # Determine insert direction from zone name
+        # split_* → bisect target tile
+        # squeeze_* → insert next to adjacent tile (fall back to split if no neighbor)
+        _OPPOSITE = {"left": "right", "right": "left", "top": "bottom", "bottom": "top"}
+        _SPLIT_DIR = {"split_left": "left", "split_right": "right",
+                      "split_top": "top",   "split_bottom": "bottom",
+                      "squeeze_left": "left","squeeze_right": "right",
+                      "squeeze_top": "top",  "squeeze_bottom": "bottom"}
+
+        direction = _SPLIT_DIR.get(zone, "left")
+
+        if zone.startswith("squeeze_"):
+            neighbor = self._adjacent_tile(target_idx, direction)
+            if neighbor is not None:
+                # Insert dragged tile to the opposite side of the neighbor
+                # so it lands between neighbor and target
+                new_tree = _tree_remove(self._tree, dragged_idx)
+                if new_tree is None:
+                    self._reposition_tiles(); return
+                new_tree = _tree_equalize_ratios(
+                    _tree_insert(new_tree, neighbor, dragged_idx, _OPPOSITE[direction])
+                )
+                self._tree = new_tree
+                if self._cfg_ref is not None:
+                    self._cfg_ref.tree = new_tree
                 self._reposition_tiles()
+                self.arrangement_changed.emit()
                 return
-            new_tree = _tree_equalize_ratios(_tree_insert(new_tree, target_idx, dragged_idx, zone))
+            # No neighbor — fall through to split behaviour
+
+        # split (or squeeze with no neighbor)
+        new_tree = _tree_remove(self._tree, dragged_idx)
+        if new_tree is None:
+            self._reposition_tiles()
+            return
+        new_tree = _tree_equalize_ratios(_tree_insert(new_tree, target_idx, dragged_idx, direction))
         self._tree = new_tree
         if self._cfg_ref is not None:
             self._cfg_ref.tree = new_tree
@@ -681,7 +783,10 @@ class LayoutCanvas(QFrame):
         if zone == "center":
             painter.setPen(QPen(QColor("#22c55e"), 2))
             painter.setBrush(QColor(34, 197, 94, 60))
-        else:
+        elif zone.startswith("squeeze_"):
+            painter.setPen(QPen(QColor("#f59e0b"), 2))
+            painter.setBrush(QColor(245, 158, 11, 80))
+        else:  # split_*
             painter.setPen(QPen(QColor("#3b82f6"), 2))
             painter.setBrush(QColor(59, 130, 246, 70))
         painter.drawRoundedRect(overlay, 4, 4)
@@ -765,7 +870,7 @@ class PlotWindow(QWidget):
         canvas_bar = QWidget(); canvas_bar.setObjectName("layoutCanvasBar")
         cb_lay = QVBoxLayout(canvas_bar)
         cb_lay.setContentsMargins(10, 6, 10, 8); cb_lay.setSpacing(4)
-        clbl = QLabel("LAYOUT  —  drag tiles to edges to split, center to move")
+        clbl = QLabel("LAYOUT  —  edge: split (blue)  |  edge gap: insert between (amber)  |  center: move (green)")
         clbl.setObjectName("layoutCanvasLabel")
         cb_lay.addWidget(clbl)
         self._canvas = LayoutCanvas(self.cfg.panes, self.cfg.tree, self)