Extend presize functionality

package.json

@@ -1,6 +1,6 @@
 {
 	"name": "regular-layout",
-	"version": "0.5.0",
+	"version": "0.6.0",
 	"description": "A regular CSS `grid` container",
 	"keywords": [],
 	"license": "Apache-2.0",

src/core/types.ts

@@ -100,6 +100,18 @@ export interface LayoutPath {
  */
 export interface PresizeDetail {
 	calculatePresizePaths(): Record<string, LayoutPath>;
+
+	/**
+	 * When the transition is a drag preview, the dragged panel's name and the
+	 * {@link LayoutPath} of its preview box. The dragged panel is removed from
+	 * the layout tree during a drag (so it is absent from
+	 * {@link PresizeDetail.calculatePresizePaths}), but `path.view_window` here
+	 * is exactly where the overlay renders it, letting consumers presize the
+	 * dragged panel like any other. `null` when the pointer is outside every
+	 * drop target (the dragged panel is hidden), `undefined` for non-drag
+	 * transitions.
+	 */
+	overlay?: { slot: string; path: LayoutPath } | null;
 }
 
 /**

src/model/overlay_controller.ts

@@ -70,36 +70,49 @@ export class OverlayController {
 			);
 		}
 
-		await host.presizeQueue.run(panel, () => {
-			if (mode === "grid" && drop_target) {
-				const path: [string, string] = [slot, drop_target?.slot];
-				const css = create_css_grid_layout(panel, path, host.physics);
-				host.stylesheet.replaceSync(css);
-			} else if (mode === "absolute") {
-				const grid_css = create_css_grid_layout(panel, undefined, host.physics);
-
-				while (drag_element?.tagName === "SLOT" && drag_element) {
-					drag_element = (
-						drag_element as HTMLSlotElement
-					).assignedElements()[0];
+		// The dragged panel is removed from `panel` above, so it is absent from
+		// the presize paths - `drop_target` carries its preview box instead
+		// (null when the pointer is outside every drop target and the dragged
+		// panel is hidden).
+		const overlay = drop_target ? { slot, path: drop_target } : null;
+		await host.presizeQueue.run(
+			panel,
+			() => {
+				if (mode === "grid" && drop_target) {
+					const path: [string, string] = [slot, drop_target?.slot];
+					const css = create_css_grid_layout(panel, path, host.physics);
+					host.stylesheet.replaceSync(css);
+				} else if (mode === "absolute") {
+					const grid_css = create_css_grid_layout(
+						panel,
+						undefined,
+						host.physics,
+					);
+
+					while (drag_element?.tagName === "SLOT" && drag_element) {
+						drag_element = (
+							drag_element as HTMLSlotElement
+						).assignedElements()[0];
+					}
+
+					const margin = drag_element
+						? getComputedStyle(drag_element)
+						: undefined;
+
+					const overlay_css = updateOverlaySheet(
+						slot,
+						box,
+						style,
+						drop_target,
+						host.physics,
+						margin,
+					);
+
+					host.stylesheet.replaceSync([grid_css, overlay_css].join("\n"));
 				}
-
-				const margin = drag_element
-					? getComputedStyle(drag_element)
-					: undefined;
-
-				const overlay_css = updateOverlaySheet(
-					slot,
-					box,
-					style,
-					drop_target,
-					host.physics,
-					margin,
-				);
-
-				host.stylesheet.replaceSync([grid_css, overlay_css].join("\n"));
-			}
-		});
+			},
+			overlay,
+		);
 
 		const event_name = `${host.physics.CUSTOM_EVENT_NAME_PREFIX}-before-update`;
 		const custom_event = new CustomEvent<Layout>(event_name, {

src/model/presize_queue.ts

@@ -9,9 +9,15 @@
 // ┃  *  [Apache License 2.0](https://www.apache.org/licenses/LICENSE-2.0). *  ┃
 // ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
 
-import type { Layout, PresizeDetail } from "../core/types.ts";
+import type { Layout, LayoutPath, PresizeDetail } from "../core/types.ts";
 import { calculate_presize_paths } from "../layout/calculate_presize_paths.ts";
 
+/**
+ * The dragged panel's preview geometry during a drag transition - see
+ * {@link PresizeDetail.overlay}.
+ */
+export type PresizeOverlay = { slot: string; path: LayoutPath } | null;
+
 /**
  * Manages cancelable pre-resize gating for layout updates.
  *
@@ -22,27 +28,40 @@ import { calculate_presize_paths } from "../layout/calculate_presize_paths.ts";
  */
 export class PresizeQueue {
 	#resizing = false;
-	#queued: { layout: Layout; fn: () => void } | null = null;
+	#queued: {
+		layout: Layout;
+		fn: () => void;
+		overlay?: PresizeOverlay;
+	} | null = null;
 	#pending: (() => void) | null = null;
 
 	constructor(
 		private _target: EventTarget,
 		private _eventName: string,
+		private _onDispatch?: () => void,
 	) {}
 
-	async run(layout: Layout, fn: () => void): Promise<void> {
+	async run(
+		layout: Layout,
+		fn: () => void,
+		overlay?: PresizeOverlay,
+	): Promise<void> {
 		if (this.#resizing) {
-			this.#queued = { layout, fn };
+			this.#queued = { layout, fn, overlay };
 			return;
 		}
 
 		this.#resizing = true;
 		try {
-			await this.#dispatchAndMaybeWait(layout, fn);
+			await this.#dispatchAndMaybeWait(layout, fn, overlay);
 			while (this.#queued) {
-				const { layout: nextLayout, fn: nextFn } = this.#queued;
+				const {
+					layout: nextLayout,
+					fn: nextFn,
+					overlay: nextOverlay,
+				} = this.#queued;
 				this.#queued = null;
-				await this.#dispatchAndMaybeWait(nextLayout, nextFn);
+				await this.#dispatchAndMaybeWait(nextLayout, nextFn, nextOverlay);
 			}
 		} finally {
 			this.#resizing = false;
@@ -57,9 +76,15 @@ export class PresizeQueue {
 		}
 	}
 
-	async #dispatchAndMaybeWait(layout: Layout, fn: () => void): Promise<void> {
+	async #dispatchAndMaybeWait(
+		layout: Layout,
+		fn: () => void,
+		overlay?: PresizeOverlay,
+	): Promise<void> {
+		this._onDispatch?.();
 		const detail: PresizeDetail = {
 			calculatePresizePaths: () => calculate_presize_paths(layout),
+			overlay,
 		};
 
 		const event = new CustomEvent(this._eventName, {

src/regular-layout-frame.ts

@@ -27,7 +27,7 @@ const CSS = `
 `;
 
 const HTML_TEMPLATE = `
-	<div part="titlebar"><div class="tabs"><slot name="tab"><regular-layout-tab></regular-layout-tab></slot></div></div>
+	<div part="titlebar"><div class="tabs" part="titlebar-track"><slot name="tab"><regular-layout-tab></regular-layout-tab></slot></div></div>
 	<div part="container"><slot></slot></div>
 `;
 

src/regular-layout.ts

@@ -130,6 +130,7 @@ export class RegularLayout extends HTMLElement {
 	private _presizeQueue: PresizeQueue;
 	private _overlayController: OverlayController;
 	private _maximized?: string;
+	private _resize_observer?: ResizeObserver;
 
 	constructor() {
 		super();
@@ -141,7 +142,13 @@ export class RegularLayout extends HTMLElement {
 		this._cursor_stylesheet = new CSSStyleSheet();
 		this._cursor_override = false;
 		const event_name = `${this._physics.CUSTOM_EVENT_NAME_PREFIX}-before-resize`;
-		this._presizeQueue = new PresizeQueue(this, event_name);
+		// Refresh the bounds cache once per layout transition, so consumers
+		// reading coordinates from a `before-resize` handler always see the
+		// element's current position - a `ResizeObserver` alone can't catch
+		// position-only moves of the host.
+		this._presizeQueue = new PresizeQueue(this, event_name, () => {
+			this._dimensions = undefined;
+		});
 		this._overlayController = new OverlayController(this.create_overlay_host());
 		this._shadowRoot.adoptedStyleSheets = [
 			this._stylesheet,
@@ -150,13 +157,19 @@ export class RegularLayout extends HTMLElement {
 	}
 
 	connectedCallback() {
+		this._resize_observer ??= new ResizeObserver(() => {
+			this._dimensions = undefined;
+		});
+
+		this._resize_observer.observe(this);
 		this.addEventListener("dblclick", this.onDblClick);
 		this.addEventListener("pointerdown", this.onPointerDown);
 		this.addEventListener("pointerup", this.onPointerUp);
 		this.addEventListener("pointermove", this.onPointerMove);
 	}
 
 	disconnectedCallback() {
+		this._resize_observer?.disconnect();
 		this.removeEventListener("dblclick", this.onDblClick);
 		this.removeEventListener("pointerdown", this.onPointerDown);
 		this.removeEventListener("pointerup", this.onPointerUp);
@@ -334,34 +347,54 @@ export class RegularLayout extends HTMLElement {
 	 * {@link save}, and any subsequent {@link restore} resets the layout to the
 	 * minimized (normal, multi-panel) view.
 	 *
+	 * Before applying, dispatches a cancelable `regular-layout-before-resize`
+	 * event (as {@link restore} does) whose paths describe the post-maximize
+	 * geometry - a single full-window entry for `name`. If the event is
+	 * cancelled via `preventDefault()`, the update is suspended until
+	 * {@link resumeResize} is called.
+	 *
 	 * Has no effect if `name` is not present in the current layout.
 	 *
 	 * @param name - The name of the panel to maximize.
 	 */
-	maximize = (name: string) => {
+	maximize = async (name: string) => {
 		if (!this.getPanel(name)) {
 			return;
 		}
 
-		this._maximized = name;
-		this._stylesheet.replaceSync(
-			create_css_maximize_layout(name, this._physics),
-		);
+		// The post-maximize geometry as a `Layout`: `name` alone, full-window.
+		// Panels hidden by the maximize are absent from the presize paths,
+		// consistent with `calculate_presize_paths`' visible-panels-only
+		// semantics.
+		const layout: Layout = { type: "tab-layout", tabs: [name], selected: 0 };
+		await this._presizeQueue.run(layout, () => {
+			this._maximized = name;
+			this._stylesheet.replaceSync(
+				create_css_maximize_layout(name, this._physics),
+			);
+		});
 	};
 
 	/**
 	 * Restores the normal multi-panel view after a {@link maximize}, without
 	 * altering the layout tree. No-op if no panel is currently maximized.
+	 *
+	 * Before applying, dispatches a cancelable `regular-layout-before-resize`
+	 * event (as {@link restore} does) with paths for the restored multi-panel
+	 * geometry. If the event is cancelled via `preventDefault()`, the update
+	 * is suspended until {@link resumeResize} is called.
 	 */
-	minimize = () => {
+	minimize = async () => {
 		if (this._maximized === undefined) {
 			return;
 		}
 
-		this._maximized = undefined;
-		this._stylesheet.replaceSync(
-			create_css_grid_layout(this._panel, undefined, this._physics),
-		);
+		await this._presizeQueue.run(this._panel, () => {
+			this._maximized = undefined;
+			this._stylesheet.replaceSync(
+				create_css_grid_layout(this._panel, undefined, this._physics),
+			);
+		});
 	};
 
 	/**
@@ -371,6 +404,7 @@ export class RegularLayout extends HTMLElement {
 	 * @param layout - The layout tree to restore
 	 */
 	restoreSync = (layout: Layout, _is_flattened: boolean = false) => {
+		this._dimensions = undefined;
 		this._maximized = undefined;
 		this._panel = !_is_flattened ? flatten(layout) : layout;
 		const css = create_css_grid_layout(this._panel, undefined, this._physics);