Documentation

Divider orientation. AxisV draws a vertical divider (panes left/right), AxisH draws a horizontal divider (panes stacked top/bottom).

Binary split tree node. Pane and split ids share one monotonic counter. Positional (non-record) so the multi-constructor type keeps total fields.

Result of dropping a dragged pane on a target pane.

Pane ids in the tree (depth-first, A then B).

Number of panes.

Does a pane with the given id exist?

Minimum (width, height) that must be reserved for a subtree under a minSize per-pane floor and spacing between every split level.

The subtree minima that apply along a split's main axis: widths for AxisV (panes left/right), heights for AxisH (panes stacked).

Extent of a region along a split's main axis.

A-side extent for a split along its main axis, honouring the subtree minima. The ratio shares out the extent left after the gutter between the sides, so a 0.5 split gives both sides the same length. Falls back to the raw share when the region is too small to satisfy both minima.

Lay out a tree into per-pane regions and divider bands within Rect. Dividers are reported parent-before-child so dragging a divider resizes its immediate subtrees relative to the same region.

Per-split divider information: the split's own region (where the ratio applies), the exact spacing band, and the axis ratio id.

Split the pane (first arg) along the axis with a 0.5 ratio, inserting the new pane. newOnA places the new pane on the A (left/top) side of the new split; False puts it on the B (right/bottom) side. Returns the updated tree (unchanged if the pane does not exist).

Set the raw ratio of a split (clamped to [0,1]).

Remove a pane. The sibling subtree absorbs its space. Nothing if the pane does not exist or removing it would empty the tree.

Move a pane onto a drop target. Center drops swap the two panes; edge drops split the target pane with the given fresh split id and move the dragged pane into the new child; top-level drops wrap the whole tree in a new root split with the dragged pane on one side.

Clamp a proposed ratio for a split so both subtrees keep at least their minimum size within the given region.

Drop preview for a drop target: the rect to highlight and the PaneDrop the drop performs. The highlight is found by simulating the drop (treeMovePane with a throwaway split id) and laying the resulting tree out (layoutNode) into the grid rect, so it is exactly the region the dragged pane will occupy after the drop, accounting for the restructuring that removing the pane causes (its parent split collapses and sibling subtrees expand) and for spacing and min-size floors. Estimating the rect from the target's pre-drop bounds goes wrong wherever mixed AxisV / AxisH splits make those two layouts diverge. spacing must be the gutter actually laid out between panes: PaneGrid passes pgSpacing + 2 * pgLeeway, not pgSpacing, or the preview regions drift from the on-screen layout. Nothing when the drop cannot be performed (unknown pane ids, DropTop on a single-pane grid).

Classify a drop point on a target pane into the PaneDrop the drop performs: the pane's center swaps the two panes, an edge zone splits the target along that edge's axis with the dragged pane on the near side.

Classify a drop point against the grid's outer boundary. If the pointer sits within band px of a grid edge, return the DropTop target for that edge; otherwise Nothing. Checked before pane-level drops so the outermost edge always restructures the whole grid.