Make drag & drop performant in all layouts

While also giving the logic for drag & drop of a floating tile a common home in the view model layer.

src/components/CallFooterViewModel.test.ts

@@ -6,12 +6,11 @@ Please see LICENSE in the repository root for full details.
 */
 
 import { describe, expect, it, vi } from "vitest";
-import { BehaviorSubject } from "rxjs";
 
 import { testScope, mockMuteStates, mockMediaDevices } from "../utils/test";
 import { constant } from "../state/Behavior";
 import type { CallViewModel } from "../state/CallViewModel/CallViewModel";
-import type { Alignment, Layout } from "../state/layout-types";
+import type { Layout } from "../state/layout-types";
 import type { SpotlightTileViewModel } from "../state/TileViewModel";
 import type { DeviceLabel } from "../state/MediaDevices";
 import { createCallFooterViewModel } from "./CallFooterViewModel";
@@ -65,10 +64,6 @@ function buildMinimalCallViewModel(layout: Layout): CallViewModel {
 const gridLayout: Layout = {
   type: "grid",
   grid: [],
-  spotlightAlignment$: new BehaviorSubject<Alignment>({
-    inline: "end",
-    block: "end",
-  }),
   setVisibleTiles: (_: number) => {},
 };
 

src/grid/CallLayout.test.tsx

@@ -13,7 +13,7 @@ import { arrangeTiles, type Bounds } from "./CallLayout";
 import { makeGridLayout } from "./GridLayout";
 import { makeSpotlightLandscapeLayout } from "./SpotlightLandscapeLayout";
 import { makeSpotlightPortraitLayout } from "./SpotlightPortraitLayout";
-import { type DragCallback, type LayoutProps } from "./Grid";
+import { type LayoutProps } from "./Grid";
 import { constant } from "../state/Behavior";
 import {
   type Alignment,
@@ -53,33 +53,6 @@ describe("grid layout", () => {
       `${Math.floor(arrangeTiles(400, 300, 3).tileWidth)}px`,
     );
   });
-
-  it("moves the spotlight only when a drag reaches another corner", () => {
-    const model = gridModel();
-    const { fixed: Fixed } = makeGridLayout({ minBounds$: bounds });
-    render(<Fixed model={model} Slot={Slot} />);
-    const alignments: Alignment[] = [];
-    model.spotlightAlignment$.subscribe((a) => alignments.push(a));
-    const drag = drags.get("spotlight")!;
-
-    // Still in the bottom right corner
-    act(() => drag({ x: 0, y: 0, xRatio: 0.9, yRatio: 0.9 }));
-    // Over to the bottom left
-    act(() => drag({ x: 0, y: 0, xRatio: 0.1, yRatio: 0.9 }));
-    // And a little further, still bottom left
-    act(() => drag({ x: 0, y: 0, xRatio: 0.2, yRatio: 0.8 }));
-    // Up to the top left
-    act(() => drag({ x: 0, y: 0, xRatio: 0.2, yRatio: 0.1 }));
-
-    expect(alignments).toEqual([
-      { inline: "end", block: "end" },
-      { inline: "start", block: "end" },
-      { inline: "start", block: "start" },
-    ]);
-    const slot = screen.getByTestId("slot-spotlight");
-    expect(slot.getAttribute("data-inline-alignment")).toBe("start");
-    expect(slot.getAttribute("data-block-alignment")).toBe("start");
-  });
 });
 
 describe("spotlight landscape layout", () => {
@@ -123,11 +96,15 @@ const bounds = constant<Bounds>({ width: 800, height: 600 });
 
 // The layouts only pass tile view models through to their slots
 const media = {} as UserMediaViewModel;
-const spotlight = new SpotlightTileViewModel(
+const spotlight = {
+  vm: new SpotlightTileViewModel(
     constant([]),
     constant(false),
     constant("solid"),
-);
+  ),
+  alignment$: constant<Alignment>({ inline: "end", block: "end" }),
+  onDrag: () => {},
+};
 const tiles = (): GridTileViewModel[] =>
   Array.from({ length: 3 }, () => new GridTileViewModel(constant(media)));
 
@@ -136,10 +113,6 @@ function gridModel(): GridLayout {
     type: "grid",
     spotlight,
     grid: tiles(),
-    spotlightAlignment$: new BehaviorSubject<Alignment>({
-      inline: "end",
-      block: "end",
-    }),
     setVisibleTiles: () => {},
   };
 }
@@ -162,22 +135,17 @@ function portraitModel(): SpotlightPortraitLayout {
   };
 }
 
-// Slots record their drag callback so a test can drag them, and show the id
+// Slots show the id of the tile they hold
-// of the tile they hold
-const drags = new Map<string, DragCallback | undefined>();
 const Slot: LayoutProps<unknown, TileViewModel, HTMLDivElement>["Slot"] = ({
   id,
   model,
   onDrag,
   ...props
-}) => {
+}) => (
-  drags.set(id, onDrag);
-  return (
   <div data-testid={`slot-${id}`} {...props}>
     {model instanceof GridTileViewModel ? model.id : "spotlight"}
   </div>
 );
-};
 
 function slotIds(): string[] {
   return screen

src/grid/Grid.tsx

@@ -40,6 +40,7 @@ import { useMergedRefs } from "../useMergedRefs";
 import { TileWrapper } from "./TileWrapper";
 import { usePrefersReducedMotion } from "../usePrefersReducedMotion";
 import { useInitial } from "../useInitial";
+import { type DragCallback } from "../state/layout-types";
 
 const MAX_ANIMATED_TILES = 50; // Capped for performance reasons
 
@@ -83,7 +84,10 @@ interface DragState {
   cursorY: number;
 }
 
-interface SlotProps<Model> extends Omit<ComponentProps<"div">, "onDrag"> {
+export interface SlotProps<Model> extends Omit<
+  ComponentProps<"div">,
+  "onDrag"
+> {
   id: string;
   model: Model;
   onDrag?: DragCallback;
@@ -181,31 +185,6 @@ export interface TileProps<Model, R extends HTMLElement> {
   model: Model;
 }
 
-interface Drag {
-  /**
-   * The X coordinate of the dragged tile in grid space.
-   */
-  x: number;
-  /**
-   * The Y coordinate of the dragged tile in grid space.
-   */
-  y: number;
-  /**
-   * The X coordinate of the dragged tile, as a scalar of the grid width.
-   */
-  xRatio: number;
-  /**
-   * The Y coordinate of the dragged tile, as a scalar of the grid height.
-   */
-  yRatio: number;
-  /**
-   * Whether this event ends the drag gesture.
-   */
-  endOfGesture: boolean
-}
-
-export type DragCallback = (drag: Drag) => void;
-
 interface LayoutMemoProps<
   LayoutModel,
   TileModel,

src/grid/GridLayout.tsx

@@ -8,15 +8,21 @@ Please see LICENSE in the repository root for full details.
 import {
   type CSSProperties,
   type ReactNode,
-  useCallback,
   useMemo,
+  type FC,
+  type ComponentType,
 } from "react";
 
 import { type GridLayout as GridLayoutModel } from "../state/layout-types.ts";
 import styles from "./GridLayout.module.css";
 import { type CallLayout, arrangeTiles } from "./CallLayout";
-import { type DragCallback, useUpdateLayout, useVisibleTiles } from "./Grid";
+import { type SlotProps, useUpdateLayout, useVisibleTiles } from "./Grid";
 import { useBehavior } from "../useBehavior";
+import {
+  type SpotlightTileViewModel,
+  type TileViewModel,
+} from "../state/TileViewModel.ts";
+import { type FloatingTile } from "../state/FloatingTile.ts";
 
 interface GridCSSProperties extends CSSProperties {
   "--gap": string;
@@ -24,6 +30,27 @@ interface GridCSSProperties extends CSSProperties {
   "--height": string;
 }
 
+interface SpotlightSlotProps {
+  model: FloatingTile & { vm: SpotlightTileViewModel };
+  Slot: ComponentType<SlotProps<TileViewModel>>;
+}
+
+const SpotlightSlot: FC<SpotlightSlotProps> = ({ model, Slot }) => {
+  useUpdateLayout();
+  const alignment = useBehavior(model.alignment$);
+
+  return (
+    <Slot
+      className={styles.slot}
+      id="spotlight"
+      model={model.vm}
+      onDrag={model.onDrag}
+      data-block-alignment={alignment.block}
+      data-inline-alignment={alignment.inline}
+    />
+  );
+};
+
 /**
  * An implementation of the "grid" layout, in which all participants are shown
  * together in a scrolling grid.
@@ -37,32 +64,10 @@ export const makeGridLayout: CallLayout<GridLayoutModel> = ({
   // lives
   fixed: function GridLayoutFixed({ ref, model, Slot }): ReactNode {
     useUpdateLayout();
-    const alignment = useBehavior(model.spotlightAlignment$);
-
-    const onDragSpotlight: DragCallback = useCallback(
-      ({ xRatio, yRatio }) => {
-        const block = yRatio < 0.5 ? "start" : "end";
-        const inline = xRatio < 0.5 ? "start" : "end";
-        // A drag reports the same alignment on every move; only a change is
-        // worth a re-render
-        const current = model.spotlightAlignment$.value;
-        if (current.block !== block || current.inline !== inline)
-          model.spotlightAlignment$.next({ block, inline });
-      },
-      [model.spotlightAlignment$],
-    );
-
     return (
       <div ref={ref} className={styles.fixed}>
         {model.spotlight && (
-          <Slot
+          <SpotlightSlot model={model.spotlight} Slot={Slot} />
-            className={styles.slot}
-            id="spotlight"
-            model={model.spotlight}
-            onDrag={onDragSpotlight}
-            data-block-alignment={alignment.block}
-            data-inline-alignment={alignment.inline}
-          />
         )}
       </div>
     );

src/grid/OneOnOneDesktopLayout.tsx

@@ -6,13 +6,13 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-import { type ReactNode, useCallback, useMemo } from "react";
+import { type ReactNode, useMemo } from "react";
 import classNames from "classnames";
 
 import { type OneOnOneDesktopLayout as OneOnOneDesktopLayoutModel } from "../state/layout-types.ts";
 import { type CallLayout, arrangeTiles } from "./CallLayout";
 import styles from "./OneOnOneDesktopLayout.module.css";
-import { type DragCallback, useUpdateLayout } from "./Grid";
+import { useUpdateLayout } from "./Grid";
 import { useBehavior } from "../useBehavior";
 
 /**
@@ -37,21 +37,12 @@ export const makeOneOnOneDesktopLayout: CallLayout<
   }): ReactNode {
     useUpdateLayout();
     const { width, height } = useBehavior(minBounds$);
-    const pipAlignment = useBehavior(model.pipAlignment$);
+    const pipAlignment = useBehavior(model.pip.alignment$);
     const { tileWidth, tileHeight } = useMemo(
       () => arrangeTiles(width, height, 1),
       [width, height],
     );
 
-    const onDragLocalTile: DragCallback = useCallback(
-      ({ xRatio, yRatio }) =>
-        model.pipAlignment$.next({
-          block: yRatio < 0.5 ? "start" : "end",
-          inline: xRatio < 0.5 ? "start" : "end",
-        }),
-      [model.pipAlignment$],
-    );
-
     return (
       <div ref={ref} className={styles.layer}>
         <Slot
@@ -62,9 +53,9 @@ export const makeOneOnOneDesktopLayout: CallLayout<
         >
           <Slot
             className={classNames(styles.slot, styles.local)}
-            id={model.pip.id}
+            id={model.pip.vm.id}
-            model={model.pip}
+            model={model.pip.vm}
-            onDrag={onDragLocalTile}
+            onDrag={model.pip.onDrag}
             data-block-alignment={pipAlignment.block}
             data-inline-alignment={pipAlignment.inline}
           />

src/grid/OneOnOneMobileLayout.tsx

@@ -6,14 +6,43 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-import { type ReactNode, useCallback } from "react";
+import { type ComponentType, type FC, type ReactNode } from "react";
 import classNames from "classnames";
 
 import { type OneOnOneMobileLayout as OneOnOneMobileLayoutModel } from "../state/layout-types.ts";
 import { type CallLayout } from "./CallLayout";
 import styles from "./OneOnOneMobileLayout.module.css";
-import { type DragCallback, useUpdateLayout } from "./Grid";
+import { type SlotProps, useUpdateLayout } from "./Grid";
 import { useBehavior } from "../useBehavior";
+import { type FloatingTile } from "../state/FloatingTile.ts";
+import {
+  type GridTileViewModel,
+  type TileViewModel,
+} from "../state/TileViewModel.ts";
+import { type Behavior } from "../state/Behavior.ts";
+
+interface PipSlotProps {
+  model: FloatingTile & { vm: GridTileViewModel; size$: Behavior<"sm" | "lg"> };
+  Slot: ComponentType<SlotProps<TileViewModel>>;
+}
+
+const PipSlot: FC<PipSlotProps> = ({ model, Slot }) => {
+  useUpdateLayout();
+  const size = useBehavior(model.size$);
+  const alignment = useBehavior(model.alignment$);
+
+  return (
+    <Slot
+      className={classNames(styles.pip)}
+      id={model.vm.id}
+      model={model.vm}
+      onDrag={model.onDrag}
+      data-size={size}
+      data-block-alignment={alignment.block}
+      data-inline-alignment={alignment.inline}
+    />
+  );
+};
 
 /**
  * An implementation of the "one-on-one" layout for mobile platforms, in which
@@ -44,30 +73,9 @@ export const makeOneOnOneMobileLayout: CallLayout<
     Slot,
   }): ReactNode {
     useUpdateLayout();
-    const pipSize = useBehavior(model.pipSize$);
-    const pipAlignment = useBehavior(model.pipAlignment$);
-    const onDragLocalTile: DragCallback = useCallback(
-      ({ xRatio, yRatio }) =>
-        model.pipAlignment$.next({
-          block: yRatio < 0.5 ? "start" : "end",
-          inline: xRatio < 0.5 ? "start" : "end",
-        }),
-      [model.pipAlignment$],
-    );
-
     return (
       <div ref={ref} className={styles.layer}>
-        {model.pip && (
+        {model.pip && <PipSlot model={model.pip} Slot={Slot} />}
-          <Slot
-            className={classNames(styles.pip)}
-            id={model.pip.id}
-            model={model.pip}
-            onDrag={onDragLocalTile}
-            data-size={pipSize}
-            data-block-alignment={pipAlignment.block}
-            data-inline-alignment={pipAlignment.inline}
-          />
-        )}
       </div>
     );
   },

src/grid/SpotlightExpandedLayout.tsx

@@ -5,13 +5,39 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-import { type ReactNode, useCallback } from "react";
+import { type ReactNode, type ComponentType, type FC } from "react";
 
 import { type SpotlightExpandedLayout as SpotlightExpandedLayoutModel } from "../state/layout-types.ts";
 import { type CallLayout } from "./CallLayout";
-import { type DragCallback, useUpdateLayout } from "./Grid";
+import { type SlotProps, useUpdateLayout } from "./Grid";
 import styles from "./SpotlightExpandedLayout.module.css";
 import { useBehavior } from "../useBehavior";
+import { type FloatingTile } from "../state/FloatingTile.ts";
+import {
+  type GridTileViewModel,
+  type TileViewModel,
+} from "../state/TileViewModel.ts";
+
+interface PipSlotProps {
+  model: FloatingTile & { vm: GridTileViewModel };
+  Slot: ComponentType<SlotProps<TileViewModel>>;
+}
+
+const PipSlot: FC<PipSlotProps> = ({ model, Slot }) => {
+  useUpdateLayout();
+  const alignment = useBehavior(model.alignment$);
+
+  return (
+    <Slot
+      className={styles.pip}
+      id={model.vm.id}
+      model={model.vm}
+      onDrag={model.onDrag}
+      data-block-alignment={alignment.block}
+      data-inline-alignment={alignment.inline}
+    />
+  );
+};
 
 /**
  * An implementation of the "expanded spotlight" layout, in which the spotlight
@@ -28,7 +54,6 @@ export const makeSpotlightExpandedLayout: CallLayout<
     Slot,
   }): ReactNode {
     useUpdateLayout();
-
     return (
       <div ref={ref} className={styles.layer}>
         <Slot
@@ -46,29 +71,9 @@ export const makeSpotlightExpandedLayout: CallLayout<
     Slot,
   }): ReactNode {
     useUpdateLayout();
-    const pipAlignment = useBehavior(model.pipAlignment$);
-
-    const onDragPip: DragCallback = useCallback(
-      ({ xRatio, yRatio }) =>
-        model.pipAlignment$.next({
-          block: yRatio < 0.5 ? "start" : "end",
-          inline: xRatio < 0.5 ? "start" : "end",
-        }),
-      [model.pipAlignment$],
-    );
-
     return (
       <div ref={ref} className={styles.layer}>
-        {model.pip && (
+        {model.pip && <PipSlot model={model.pip} Slot={Slot} />}
-          <Slot
-            className={styles.pip}
-            id={model.pip.id}
-            model={model.pip}
-            onDrag={onDragPip}
-            data-block-alignment={pipAlignment.block}
-            data-inline-alignment={pipAlignment.inline}
-          />
-        )}
       </div>
     );
   },

src/grid/SpotlightLandscapeLayout.tsx

@@ -40,7 +40,7 @@ export const makeSpotlightLandscapeLayout: CallLayout<
           <Slot
             className={styles.slot}
             id="spotlight"
-            model={model.spotlight}
+            model={model.spotlight.vm}
           />
         </div>
         <div className={styles.grid} />
@@ -59,7 +59,7 @@ export const makeSpotlightLandscapeLayout: CallLayout<
 
     return (
       <div ref={ref} className={styles.layer}>
-        <SpotlightSlot media$={model.spotlight.media$} />
+        <SpotlightSlot media$={model.spotlight.vm.media$} />
         <div className={styles.grid}>
           {model.grid.map((m) => (
             <Slot key={m.id} className={styles.slot} id={m.id} model={m} />

src/grid/SpotlightPortraitLayout.tsx

@@ -43,7 +43,7 @@ export const makeSpotlightPortraitLayout: CallLayout<
           <Slot
             className={styles.slot}
             id="spotlight"
-            model={model.spotlight}
+            model={model.spotlight.vm}
           />
         </div>
       </div>
@@ -65,7 +65,7 @@ export const makeSpotlightPortraitLayout: CallLayout<
       width,
       model.grid.length,
     );
-    const withIndicators = useBehavior(model.spotlight.media$).length > 1;
+    const withIndicators = useBehavior(model.spotlight.vm.media$).length > 1;
 
     return (
       <div

src/state/CallViewModel/CallViewModel.test.ts

@@ -176,7 +176,7 @@ function summarizeLayout$(l$: Observable<Layout>): Observable<LayoutSummary> {
         case "grid":
           return combineLatest(
             [
-              l.spotlight?.media$ ?? constant(undefined),
+              l.spotlight?.vm.media$ ?? constant(undefined),
               ...l.grid.map((vm) => vm.media$),
             ],
             (spotlight, ...grid) => ({
@@ -188,7 +188,7 @@ function summarizeLayout$(l$: Observable<Layout>): Observable<LayoutSummary> {
         case "spotlight-landscape":
         case "spotlight-portrait":
           return combineLatest(
-            [l.spotlight.media$, ...l.grid.map((vm) => vm.media$)],
+            [l.spotlight.vm.media$, ...l.grid.map((vm) => vm.media$)],
             (spotlight, ...grid) => ({
               type: l.type,
               spotlight: spotlight.map((vm) => vm.id),
@@ -197,7 +197,7 @@ function summarizeLayout$(l$: Observable<Layout>): Observable<LayoutSummary> {
           );
         case "spotlight-expanded":
           return combineLatest(
-            [l.spotlight.media$, l.pip?.media$ ?? constant(undefined)],
+            [l.spotlight.media$, l.pip?.vm.media$ ?? constant(undefined)],
             (spotlight, pip) => ({
               type: l.type,
               spotlight: spotlight.map((vm) => vm.id),
@@ -206,7 +206,7 @@ function summarizeLayout$(l$: Observable<Layout>): Observable<LayoutSummary> {
           );
         case "one-on-one-desktop":
           return combineLatest(
-            [l.spotlight.media$, l.pip.media$],
+            [l.spotlight.media$, l.pip.vm.media$],
             (spotlight, pip) => ({
               type: l.type,
               spotlight: spotlight.id,
@@ -217,8 +217,8 @@ function summarizeLayout$(l$: Observable<Layout>): Observable<LayoutSummary> {
           return combineLatest(
             [
               l.spotlight.media$,
-              l.pip?.media$ ?? constant(undefined),
+              l.pip?.vm.media$ ?? constant(undefined),
-              l.pipSize$,
+              l.pip?.size$ ?? constant(undefined),
             ],
             (spotlight, pip, pipSize) => ({
               type: l.type,
@@ -480,7 +480,7 @@ describe.each(modes)("CallViewModel (%s mode)", (mode) => {
                 type: "one-on-one-mobile",
                 spotlight: [`${aliceId}:0`],
                 pip: undefined,
-                pipSize: "lg",
+                pipSize: undefined,
               },
               b: {
                 type: "one-on-one-mobile",
@@ -518,7 +518,7 @@ describe.each(modes)("CallViewModel (%s mode)", (mode) => {
               type: "one-on-one-mobile",
               spotlight: [`${aliceId}:0`],
               pip: undefined,
-              pipSize: "lg",
+              pipSize: undefined,
             },
           });
           // It wouldn't be clear whether Alice or Bob is the remote video tile,
@@ -566,7 +566,7 @@ describe.each(modes)("CallViewModel (%s mode)", (mode) => {
                 type: "one-on-one-mobile",
                 spotlight: [`${aliceId}:0`],
                 pip: undefined,
-                pipSize: "sm",
+                pipSize: undefined,
               },
               b: {
                 type: "spotlight-landscape",
@@ -765,7 +765,7 @@ describe.each(modes)("CallViewModel (%s mode)", (mode) => {
                 type: "one-on-one-mobile",
                 spotlight: [`${aliceId}:0`],
                 pip: undefined,
-                pipSize: "lg",
+                pipSize: undefined,
               },
               b: {
                 // In a larger window, expect the one-on-one desktop layout

src/state/CallViewModel/CallViewModel.ts

@@ -93,7 +93,6 @@ import { type ProcessorState } from "../../livekit/TrackProcessorContext";
 import { type HostBridge, nullHostBridge } from "../../HostBridge";
 import {
   layoutShallowEquals,
-  type Alignment,
   type GridLayoutMedia,
   type Layout,
   type LayoutMedia,
@@ -163,6 +162,7 @@ import {
   type RingingMediaViewModel,
 } from "../media/RingingMediaViewModel.ts";
 import { type GridTileViewModel } from "../TileViewModel.ts";
+import { createFloatingTile } from "../FloatingTile.ts";
 
 //TODO
 // Larger rename
@@ -1548,32 +1548,28 @@ export function createCallViewModel$(
   );
 
   /**
-   * The alignment of the floating spotlight tile, if present.
+   * State of the floating spotlight tile, if present.
    */
-  const spotlightAlignment$ = new BehaviorSubject<Alignment>({
+  const floatingSpotlightTile = createFloatingTile(scope, {
     inline: "end",
     block: "end",
   });
   /**
-   * The size of the small picture-in-picture tile, if present, when in portrait.
+   * State of the small picture-in-picture tile, if present, when in landscape.
    */
-  const portraitPipSize$ = scope.behavior(
+  const landscapePipTile = createFloatingTile(scope, {
-    showFooter$.pipe(map((showFooter) => (showFooter ? "lg" : "sm"))),
-  );
-  /**
-   * The alignment of the small picture-in-picture tile, if present, when in portrait.
-   */
-  const portraitPipAlignment$ = new BehaviorSubject<Alignment>({
-    inline: "end",
-    block: "end",
-  });
-  /**
-   * The alignment of the small picture-in-picture tile, if present, when in landscape.
-   */
-  const landscapePipAlignment$ = new BehaviorSubject<Alignment>({
     inline: "end",
     block: "start",
   });
+  /**
+   * State of the small picture-in-picture tile, if present, when in portrait.
+   */
+  const portraitPipTile = {
+    ...createFloatingTile(scope, { inline: "end", block: "end" }),
+    size$: scope.behavior(
+      showFooter$.pipe(map((showFooter) => (showFooter ? "lg" : "sm"))),
+    ),
+  };
 
   // There is a cyclical dependency here: the layout algorithms want to know
   // which tiles are on screen, but to know which tiles are on screen we have to
@@ -1603,7 +1599,7 @@ export function createCallViewModel$(
             case "spotlight-portrait":
               [layout, newTiles] = gridLikeLayout(
                 media,
-                spotlightAlignment$,
+                floatingSpotlightTile,
                 visibleTiles,
                 setVisibleTiles,
                 prevTiles,
@@ -1613,26 +1609,25 @@ export function createCallViewModel$(
             case "spotlight-expanded":
               [layout, newTiles] = spotlightExpandedLayout(
                 media,
-                landscapePipAlignment$,
+                landscapePipTile,
                 prevTiles,
               );
               break;
             case "one-on-one-desktop":
               [layout, newTiles] = oneOnOneDesktopLayout(
                 media,
-                landscapePipAlignment$,
+                landscapePipTile,
                 prevTiles,
               );
-              pip = layout.pip;
+              pip = layout.pip.vm;
               break;
             case "one-on-one-mobile":
               [layout, newTiles] = oneOnOneMobileLayout(
                 media,
-                portraitPipSize$,
+                portraitPipTile,
-                portraitPipAlignment$,
                 prevTiles,
               );
-              pip = layout.pip;
+              pip = layout.pip?.vm;
               break;
             case "pip":
               [layout, newTiles] = pipLayout(media, prevTiles);

src/state/FloatingTile.test.ts

@@ -0,0 +1,38 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { test } from "vitest";
+import { withTestScheduler } from "../utils/test";
+import { createFloatingTile } from "./FloatingTile";
+
+test("FloatingTile changes alignment on drag", () =>
+  withTestScheduler(({ scope, expectObservable, schedule }) => {
+    // Tile starts in the top left
+    const { alignment$, onDrag } = createFloatingTile(scope, {
+      inline: "start",
+      block: "start",
+    });
+    // Drag to all four corners, and then repeatedly into the top left.
+    schedule("-↗↘↙↖↖", {
+      "↗": () =>
+        onDrag({ x: 100, y: 0, xRatio: 1, yRatio: 0, endOfGesture: false }),
+      "↘": () =>
+        onDrag({ x: 100, y: 100, xRatio: 1, yRatio: 1, endOfGesture: false }),
+      "↙": () =>
+        onDrag({ x: 0, y: 100, xRatio: 0, yRatio: 1, endOfGesture: false }),
+      "↖": () =>
+        onDrag({ x: 0, y: 0, xRatio: 0, yRatio: 0, endOfGesture: false }),
+    });
+    // Alignment should change accordingly. Notably, the alignment should *not*
+    // update when repeatedly dragged into the same corner, for performance.
+    expectObservable(alignment$).toBe("↖↗↘↙↖-", {
+      "↗": { inline: "end", block: "start" },
+      "↘": { inline: "end", block: "end" },
+      "↙": { inline: "start", block: "end" },
+      "↖": { inline: "start", block: "start" },
+    });
+  }));

src/state/FloatingTile.ts

@@ -0,0 +1,43 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { distinctUntilChanged, map, startWith, Subject } from "rxjs";
+
+import { type Behavior } from "./Behavior";
+import { type DragCallback, type Alignment, type Drag } from "./layout-types";
+import { type ObservableScope } from "./ObservableScope";
+
+/**
+ * Represents a floating tile which may be dragged to different corners of the
+ * call interface.
+ */
+export interface FloatingTile {
+  alignment$: Behavior<Alignment>;
+  onDrag: DragCallback;
+}
+
+export function createFloatingTile(
+  scope: ObservableScope,
+  defaultAlignment: Alignment,
+): FloatingTile {
+  const dragEvents$ = new Subject<Drag>();
+  return {
+    alignment$: scope.behavior(
+      dragEvents$.pipe(
+        map<Drag, Alignment>(({ xRatio, yRatio }) => ({
+          inline: xRatio < 0.5 ? "start" : "end",
+          block: yRatio < 0.5 ? "start" : "end",
+        })),
+        startWith(defaultAlignment),
+        distinctUntilChanged(
+          (a1, a2) => a1.inline === a2.inline && a1.block === a2.block,
+        ),
+      ),
+    ),
+    onDrag: (drag) => dragEvents$.next(drag),
+  };
+}

src/state/GridLikeLayout.ts

@@ -5,14 +5,9 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-import { type BehaviorSubject } from "rxjs";
+import { type Layout, type LayoutMedia } from "./layout-types.ts";
-
-import {
-  type Alignment,
-  type Layout,
-  type LayoutMedia,
-} from "./layout-types.ts";
 import { type TileStore } from "./TileStore";
+import { type FloatingTile } from "./FloatingTile.ts";
 
 export type GridLikeLayoutType =
   | "grid"
@@ -25,7 +20,7 @@ export type GridLikeLayoutType =
  */
 export function gridLikeLayout(
   media: LayoutMedia & { type: GridLikeLayoutType },
-  spotlightAlignment$: BehaviorSubject<Alignment>,
+  floatingSpotlightTile: FloatingTile,
   visibleTiles: number,
   setVisibleTiles: (value: number) => void,
   prevTiles: TileStore,
@@ -42,9 +37,11 @@ export function gridLikeLayout(
   return [
     {
       type: media.type,
-      spotlight: tiles.spotlightTile,
+      spotlight: tiles.spotlightTile && {
+        vm: tiles.spotlightTile,
+        ...floatingSpotlightTile,
+      },
       grid: tiles.gridTiles,
-      spotlightAlignment$,
       setVisibleTiles,
     } as Layout & { type: GridLikeLayoutType },
     tiles,

src/state/OneOnOneDesktopLayout.ts

@@ -6,21 +6,19 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-import { type BehaviorSubject } from "rxjs";
-
 import {
-  type Alignment,
   type OneOnOneDesktopLayout,
   type OneOnOneDesktopLayoutMedia,
 } from "./layout-types";
 import { type TileStore } from "./TileStore";
+import { type FloatingTile } from "./FloatingTile";
 
 /**
  * Produces a one-on-one desktop layout with the given media.
  */
 export function oneOnOneDesktopLayout(
   media: OneOnOneDesktopLayoutMedia,
-  pipAlignment$: BehaviorSubject<Alignment>,
+  pipTile: FloatingTile,
   prevTiles: TileStore,
 ): [OneOnOneDesktopLayout, TileStore] {
   const update = prevTiles.from(2);
@@ -32,8 +30,7 @@ export function oneOnOneDesktopLayout(
     {
       type: media.type,
       spotlight: tiles.gridTilesByMedia.get(media.spotlight)!,
-      pip: tiles.gridTilesByMedia.get(media.pip)!,
+      pip: { vm: tiles.gridTilesByMedia.get(media.pip)!, ...pipTile },
-      pipAlignment$,
     },
     tiles,
   ];

src/state/OneOnOneMobileLayout.ts

@@ -6,23 +6,20 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-import { type BehaviorSubject } from "rxjs";
-
 import {
-  type Alignment,
   type OneOnOneMobileLayout,
   type OneOnOneMobileLayoutMedia,
 } from "./layout-types";
 import { type TileStore } from "./TileStore";
 import { type Behavior } from "./Behavior";
+import { type FloatingTile } from "./FloatingTile";
 
 /**
  * Produces a one-on-one mobile layout with the given media.
  */
 export function oneOnOneMobileLayout(
   media: OneOnOneMobileLayoutMedia,
-  pipSize$: Behavior<"sm" | "lg">,
+  pipTile: FloatingTile & { size$: Behavior<"sm" | "lg"> },
-  pipAlignment$: BehaviorSubject<Alignment>,
   prevTiles: TileStore,
 ): [OneOnOneMobileLayout, TileStore] {
   const update = prevTiles.from(media.pip === undefined ? 0 : 1);
@@ -30,13 +27,12 @@ export function oneOnOneMobileLayout(
   if (media.pip !== undefined) update.registerGridTile(media.pip);
   const tiles = update.build();
 
+  const pipVm = media.pip && tiles.gridTilesByMedia.get(media.pip);
   return [
     {
       type: media.type,
       spotlight: tiles.spotlightTile!,
-      pip: media.pip && tiles.gridTilesByMedia.get(media.pip),
+      pip: pipVm && { vm: pipVm, ...pipTile },
-      pipSize$,
-      pipAlignment$,
     },
     tiles,
   ];

src/state/SpotlightExpandedLayout.ts

@@ -5,21 +5,19 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-import { type BehaviorSubject } from "rxjs";
-
 import {
-  type Alignment,
   type SpotlightExpandedLayout,
   type SpotlightExpandedLayoutMedia,
 } from "./layout-types";
 import { type TileStore } from "./TileStore";
+import { type FloatingTile } from "./FloatingTile";
 
 /**
  * Produces an expanded spotlight layout with the given media.
  */
 export function spotlightExpandedLayout(
   media: SpotlightExpandedLayoutMedia,
-  pipAlignment$: BehaviorSubject<Alignment>,
+  pipTile: FloatingTile,
   prevTiles: TileStore,
 ): [SpotlightExpandedLayout, TileStore] {
   const update = prevTiles.from(1);
@@ -27,12 +25,12 @@ export function spotlightExpandedLayout(
   if (media.pip !== undefined) update.registerPipTile(media.pip);
   const tiles = update.build();
 
+  const pipVm = tiles.gridTiles.at(0);
   return [
     {
       type: media.type,
       spotlight: tiles.spotlightTile!,
-      pip: tiles.gridTiles.at(0),
+      pip: pipVm && { vm: pipVm, ...pipTile },
-      pipAlignment$,
     },
     tiles,
   ];

src/state/layout-types.test.ts

@@ -6,33 +6,25 @@ Please see LICENSE in the repository root for full details.
 */
 
 import { test, expect } from "vitest";
-import {
+import { layoutShallowEquals, type Layout } from "./layout-types";
-  type Alignment,
-  layoutShallowEquals,
-  type Layout,
-} from "./layout-types";
 import {
   type SpotlightTileViewModel,
   type GridTileViewModel,
 } from "./TileViewModel";
-import { BehaviorSubject } from "rxjs";
+import { type FloatingTile } from "./FloatingTile";
 
 const spotlightTile = {} as unknown as SpotlightTileViewModel;
 const gridTile = {} as unknown as GridTileViewModel;
-const pipAlignment$ = new BehaviorSubject<Alignment>({
+const pipTile = {} as unknown as FloatingTile & { vm: GridTileViewModel };
-  inline: "end",
-  block: "end",
-});
 
 const spotlightExpanded: Layout = {
   type: "spotlight-expanded",
   spotlight: spotlightTile,
-  pipAlignment$,
 };
 
 const spotlightPortrait: Layout = {
   type: "spotlight-portrait",
-  spotlight: spotlightTile,
+  spotlight: { vm: spotlightTile },
   grid: [gridTile],
   setVisibleTiles: () => {},
 };
@@ -46,12 +38,12 @@ test("layoutShallowEquals detects a missing key", () => {
   expect(
     layoutShallowEquals(spotlightExpanded, {
       ...spotlightExpanded,
-      pip: gridTile,
+      pip: pipTile,
     }),
   ).toBe(false);
   expect(
     layoutShallowEquals(
-      { ...spotlightExpanded, pip: gridTile },
+      { ...spotlightExpanded, pip: pipTile },
       spotlightExpanded,
     ),
   ).toBe(false);

src/state/layout-types.ts

@@ -5,8 +5,6 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-import { type BehaviorSubject } from "rxjs";
-
 import { type LocalUserMediaViewModel } from "./media/LocalUserMediaViewModel.ts";
 import { type MediaViewModel } from "./media/MediaViewModel.ts";
 import { type RingingMediaViewModel } from "./media/RingingMediaViewModel.ts";
@@ -17,6 +15,7 @@ import {
 } from "./TileViewModel.ts";
 import { type Behavior } from "./Behavior.ts";
 import { shallowEquals as arrayShallowEquals } from "../utils/array.ts";
+import { type FloatingTile } from "./FloatingTile.ts";
 
 export interface GridLayoutMedia {
   type: "grid";
@@ -80,24 +79,48 @@ export interface Alignment {
   block: "start" | "end";
 }
 
+export interface Drag {
+  /**
+   * The X offset of the dragged tile relative to its container.
+   */
+  x: number;
+  /**
+   * The Y offset of the dragged tile relative to its container.
+   */
+  y: number;
+  /**
+   * The X coordinate of the dragged tile, as a scalar of the container's width.
+   */
+  xRatio: number;
+  /**
+   * The Y coordinate of the dragged tile, as a scalar of the container's height.
+   */
+  yRatio: number;
+  /**
+   * Whether this event ends the drag gesture.
+   */
+  endOfGesture: boolean;
+}
+
+export type DragCallback = (drag: Drag) => void;
+
 export interface GridLayout {
   type: "grid";
-  spotlight?: SpotlightTileViewModel;
+  spotlight?: FloatingTile & { vm: SpotlightTileViewModel };
   grid: GridTileViewModel[];
-  spotlightAlignment$: BehaviorSubject<Alignment>;
   setVisibleTiles: (value: number) => void;
 }
 
 export interface SpotlightLandscapeLayout {
   type: "spotlight-landscape";
-  spotlight: SpotlightTileViewModel;
+  spotlight: { vm: SpotlightTileViewModel };
   grid: GridTileViewModel[];
   setVisibleTiles: (value: number) => void;
 }
 
 export interface SpotlightPortraitLayout {
   type: "spotlight-portrait";
-  spotlight: SpotlightTileViewModel;
+  spotlight: { vm: SpotlightTileViewModel };
   grid: GridTileViewModel[];
   setVisibleTiles: (value: number) => void;
 }
@@ -105,23 +128,19 @@ export interface SpotlightPortraitLayout {
 export interface SpotlightExpandedLayout {
   type: "spotlight-expanded";
   spotlight: SpotlightTileViewModel;
-  pip?: GridTileViewModel;
+  pip?: FloatingTile & { vm: GridTileViewModel };
-  pipAlignment$: BehaviorSubject<Alignment>;
 }
 
 export interface OneOnOneDesktopLayout {
   type: "one-on-one-desktop";
   spotlight: GridTileViewModel;
-  pip: GridTileViewModel;
+  pip: FloatingTile & { vm: GridTileViewModel };
-  pipAlignment$: BehaviorSubject<Alignment>;
 }
 
 export interface OneOnOneMobileLayout {
   type: "one-on-one-mobile";
   spotlight: SpotlightTileViewModel;
-  pip?: GridTileViewModel;
+  pip?: FloatingTile & { vm: GridTileViewModel; size$: Behavior<"sm" | "lg"> };
-  pipSize$: Behavior<"sm" | "lg">;
-  pipAlignment$: BehaviorSubject<Alignment>;
 }
 
 export interface PipLayout {