Tab row: what does not fit goes behind a menu, the active tab always stays (#84)

Nine tabs need 631 px; at 1280x800 the centre column offers 666 px, so the tenth
tab would have spilled under the inspector - the same overflow CI caught in run 5.

TabStrip replaces the bare HStack: it fits the longest prefix that stays inside
the budget, always appends the active tab, and offers the rest behind a fixed
28 px button. The button's width is fixed on purpose - deriving it from the
number of hidden tabs would make width depend on the count and the count on the
width.

The rule itself is a pure function (tabRow.ts), so it is checked without a
browser. setActive() calls relayout() itself because Widget.resize only lays out
on a changed size, and switching tabs does not change any size.

Adding a tab now needs no space arithmetic - only a line in TAB_ORDER,
TAB_LABELS and panes, all three Record<CentreTab, ...>, so forgetting one is a
type error.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

README.md

@@ -37,7 +37,7 @@ npm run build        # writes dist/ and regenerates index.html; the folder is wh
 The browser suite and the three example games need a machine with a GPU:
 
 ```bash
-node tools/seed-e2e.mjs && node tools/e2e.mjs      # the editor, 785 checks (GM_STEPS=20 for one step)
+node tools/seed-e2e.mjs && node tools/e2e.mjs      # the editor, 790 checks (GM_STEPS=20 for one step)
 node tools/seed-jumprun.mjs && node tools/smoke-jumprun.mjs
 node tools/seed-tetris.mjs && node tools/smoke-tetris.mjs
 node tools/seed-actor.mjs && node tools/smoke-actor.mjs

src/editor/Editor.ts

@@ -4,7 +4,8 @@ import { findAsset, findObjectHolder } from '../core/model/Project';
 import type { ProjectStore } from '../core/store/ProjectStore';
 import type { FontStore } from '../core/store/FontStore';
 import type { TextureStore } from '../core/store/TextureStore';
-import { Button, clamp, HStack, Panel, Splitter, Theme, ui, VStack, type Widget } from '../ui';
+import { clamp, HStack, Panel, Splitter, Theme, ui, VStack, type Widget } from '../ui';
+import { TabStrip, type TabPlace } from './TabStrip';
 import { ConsolePanel } from './console/ConsolePanel';
 import { GameViewport } from './viewport/GameViewport';
 import { SceneViewport } from './viewport/SceneViewport';
@@ -101,12 +102,12 @@ export class Editor implements PlayHost {
   private readonly editorRun: EditorRun;
   private readonly projects: ProjectSession;
   private readonly leftColumn: VStack;
-  private readonly leftSplitter = new Splitter('x');
+  readonly leftSplitter = new Splitter('x');
-  private readonly rightSplitter = new Splitter('x');
+  readonly rightSplitter = new Splitter('x');
   readonly consoleSplitter = new Splitter('y');
   private readonly workspace: HStack;
   private readonly centre: VStack;
-  private readonly tabButtons: Record<CentreTab, Button>;
+  private readonly tabs: TabStrip<CentreTab>;
   private readonly panes: Record<CentreTab, Widget>;
   private readonly toolbar: Toolbar;
   private fpsFrames = 0;
@@ -164,8 +165,8 @@ export class Editor implements PlayHost {
     this.leftColumn.add(this.hierarchy, 1);
 
     this.centre = new VStack();
-    const tabs = new HStack({ gap: 2, padding: 4, align: 'center' });
+    this.tabs = new TabStrip(TAB_ORDER, TAB_LABELS, (tab) => this.showTab(tab));
-    tabs.minHeight = Theme.controlHeight + 8;
+    this.tabs.minHeight = Theme.controlHeight + 8;
     // Written out per tab rather than derived, because a `Record<CentreTab, …>` is what makes
     // adding a tab a type error everywhere it has to be handled instead of a silent omission.
     this.panes = {
@@ -179,24 +180,11 @@ export class Editor implements PlayHost {
       container: this.containerEditor,
       list: this.listEditor,
     };
-    this.tabButtons = {
+    this.centre.add(this.tabs);
-      scene: this.tabButton('scene'),
-      game: this.tabButton('game'),
-      graph: this.tabButton('graph'),
-      statemachine: this.tabButton('statemachine'),
-      shader: this.tabButton('shader'),
-      texture: this.tabButton('texture'),
-      animation: this.tabButton('animation'),
-      container: this.tabButton('container'),
-      list: this.tabButton('list'),
-    };
-    this.centre.add(tabs);
     for (const tab of TAB_ORDER) {
-      tabs.add(this.tabButtons[tab]);
       this.centre.add(this.panes[tab], 1);
       this.panes[tab].visible = tab === 'scene';
     }
-    this.tabButtons.scene.setToggled(true);
     // The console sits below whichever tab is showing, so it is a sibling of the panes, not of
     // the workspace: switching tabs must not move it.
     this.centre.add(this.consoleSplitter);
@@ -283,32 +271,18 @@ export class Editor implements PlayHost {
         ? () => findObjectHolder(this.state.project, this.containerEditor.currentAssetId)
         : () => this.state.activeScene,
     );
-    for (const key of TAB_ORDER) {
+    for (const key of TAB_ORDER) this.panes[key].visible = key === tab;
-      this.panes[key].visible = key === tab;
+    this.tabs.setActive(tab);
-      this.tabButtons[key].setToggled(key === tab);
-    }
     this.centre.relayout();
     ui().focus.validate();
   }
 
   /**
-   * Global x-extent of every tab button, from the widget box – not `getBounds()`, which on an
+   * Global x-extent of the tab buttons in the row, from the widget box – not `getBounds()`, which
-   * untoggled ghost tab sees nothing but the label (the background is not drawn at all).
+   * on an untoggled ghost tab sees nothing but the label (the background is not drawn at all).
    */
-  tabBounds(): Record<CentreTab, { x: number; right: number }> {
+  tabRow(): { shown: TabPlace<CentreTab>[]; hidden: CentreTab[] } {
-    const out = {} as Record<CentreTab, { x: number; right: number }>;
+    return { shown: this.tabs.places(), hidden: this.tabs.hidden() };
-    for (const tab of TAB_ORDER) {
-      const button = this.tabButtons[tab];
-      const x = button.toGlobal({ x: 0, y: 0 }).x;
-      out[tab] = { x, right: x + button.w };
-    }
-    return out;
-  }
-
-  private tabButton(tab: CentreTab): Button {
-    // Half the theme padding: nine tabs at the full 8 px overflow the centre column of a 1280 px
-    // window by 27 px, and a button past its edge sits under the inspector (measured, CI run 5).
-    return new Button(TAB_LABELS[tab], { variant: 'ghost', padding: 4, onClick: () => this.showTab(tab) });
   }
 
   boot(): Promise<void> {

src/editor/TabStrip.ts

@@ -0,0 +1,100 @@
+import { Button, HStack, Menu } from '../ui';
+import { tabRowLayout } from './tabRow';
+
+/** Fixed, so that the count of hidden tabs cannot feed back into how much room the row has. */
+const OVERFLOW_WIDTH = 28;
+
+export interface TabPlace<T extends string> {
+  tab: T;
+  x: number;
+  right: number;
+}
+
+/**
+ * The row of tab buttons. What does not fit goes behind a `»` button that opens the rest as a
+ * menu, so the row survives any window width and any number of tabs.
+ */
+export class TabStrip<T extends string> extends HStack {
+  private readonly buttons = new Map<T, Button>();
+  private readonly overflow: Button;
+  private hiddenTabs: T[] = [];
+  private active: T;
+
+  constructor(
+    private readonly order: readonly T[],
+    private readonly labels: Record<T, string>,
+    private readonly onPick: (tab: T) => void,
+  ) {
+    super({ gap: 2, padding: 4, align: 'center' });
+    this.active = order[0]!;
+    for (const tab of order) {
+      // Half the theme padding: nine tabs at the full 8 px overflow the centre column of a 1280 px
+      // window by 27 px, and a button past its edge sits under the inspector (measured, CI run 5).
+      const button = new Button(labels[tab], {
+        variant: 'ghost',
+        padding: 4,
+        onClick: () => this.onPick(tab),
+      });
+      this.buttons.set(tab, button);
+      this.add(button);
+    }
+    this.overflow = new Button('»', {
+      variant: 'ghost',
+      width: OVERFLOW_WIDTH,
+      onClick: () => this.openMenu(),
+    });
+    this.add(this.overflow);
+    this.buttons.get(this.active)!.setToggled(true);
+  }
+
+  setActive(tab: T): void {
+    this.active = tab;
+    for (const [key, button] of this.buttons) button.setToggled(key === tab);
+    // Not `resize`: the strip keeps its size while a different tab has to come into view.
+    this.relayout();
+  }
+
+  /** Global x-extent of the tab buttons currently in the row, in order. */
+  places(): TabPlace<T>[] {
+    const out: TabPlace<T>[] = [];
+    for (const tab of this.order) {
+      const button = this.buttons.get(tab)!;
+      if (!button.visible) continue;
+      const x = button.toGlobal({ x: 0, y: 0 }).x;
+      out.push({ tab, x, right: x + button.w });
+    }
+    return out;
+  }
+
+  hidden(): T[] {
+    return [...this.hiddenTabs];
+  }
+
+  override layout(): void {
+    this.applyOverflow();
+    super.layout();
+  }
+
+  private applyOverflow(): void {
+    const tabs = this.order.map((tab) => ({ key: tab, width: this.buttons.get(tab)!.measure().w }));
+    const { hidden } = tabRowLayout({
+      tabs,
+      available: this.w - this.padding * 2,
+      gap: this.gap,
+      overflowWidth: OVERFLOW_WIDTH,
+      active: this.active,
+    });
+    this.hiddenTabs = hidden;
+    const away = new Set(hidden);
+    for (const [tab, button] of this.buttons) button.visible = !away.has(tab);
+    this.overflow.visible = hidden.length > 0;
+  }
+
+  private openMenu(): void {
+    const items = this.hiddenTabs.map((tab) => ({
+      label: this.labels[tab],
+      onSelect: () => this.onPick(tab),
+    }));
+    new Menu(items).openBelow(this.overflow);
+  }
+}

src/editor/debugHook.ts

@@ -186,7 +186,9 @@ export function installDebugHook(app: Application, state: EditorState, editor: E
     textOverflows,
     labelsDropped,
     shownLabel,
-    tabBounds: () => editor.tabBounds(),
+    tabRow: () => editor.tabRow(),
+    /** The dividers left and right of the centre column – dragging them narrows the tab row. */
+    panelSplitters: () => ({ left: centreOf(editor.leftSplitter), right: centreOf(editor.rightSplitter) }),
     viewportCenter: () => centreOf(viewport),
     /** Pans the Scene tab to a world point – a step's own lane, away from what earlier steps left. */
     lookAt: (x: number, y: number) => viewport.lookAt(x, y),

src/editor/tabRow.ts

@@ -0,0 +1,50 @@
+export interface TabWidth<T extends string> {
+  key: T;
+  width: number;
+}
+
+export interface TabRowInput<T extends string> {
+  tabs: TabWidth<T>[];
+  /** Width the row may occupy, padding already taken off. */
+  available: number;
+  gap: number;
+  /** Width of the button that opens the hidden ones; only claimed when something is hidden. */
+  overflowWidth: number;
+  active: T;
+}
+
+export interface TabRowLayout<T extends string> {
+  shown: T[];
+  hidden: T[];
+}
+
+function rowWidth<T extends string>(tabs: TabWidth<T>[], gap: number): number {
+  if (tabs.length === 0) return 0;
+  return tabs.reduce((sum, tab) => sum + tab.width, 0) + gap * (tabs.length - 1);
+}
+
+/**
+ * Which tabs fit in the row and which go behind the overflow button. Tabs keep their order; the
+ * active one is always shown, even if the row can hold nothing else.
+ */
+export function tabRowLayout<T extends string>(input: TabRowInput<T>): TabRowLayout<T> {
+  const { tabs, available, gap, overflowWidth, active } = input;
+  if (rowWidth(tabs, gap) <= available) return { shown: tabs.map((tab) => tab.key), hidden: [] };
+
+  const budget = available - overflowWidth - gap;
+  const shown: TabWidth<T>[] = [];
+  for (const tab of tabs) {
+    if (rowWidth([...shown, tab], gap) > budget) break;
+    shown.push(tab);
+  }
+  if (!shown.some((tab) => tab.key === active)) {
+    const activeTab = tabs.find((tab) => tab.key === active);
+    if (activeTab) {
+      // The prefix stops before the active tab, so appending it keeps the row in order.
+      while (shown.length > 0 && rowWidth([...shown, activeTab], gap) > budget) shown.pop();
+      shown.push(activeTab);
+    }
+  }
+  const kept = new Set(shown.map((tab) => tab.key));
+  return { shown: [...kept], hidden: tabs.map((tab) => tab.key).filter((key) => !kept.has(key)) };
+}

tests/editor/tab-row.test.ts

@@ -0,0 +1,49 @@
+import { describe, expect, it } from 'vitest';
+import { tabRowLayout } from '../../src/editor/tabRow';
+
+/** The nine tabs as measured in the browser at padding 4, in their editor order. */
+const TABS = [
+  { key: 'scene', width: 53 },
+  { key: 'game', width: 50 },
+  { key: 'graph', width: 74 },
+  { key: 'statemachine', width: 114 },
+  { key: 'shader', width: 61 },
+  { key: 'texture', width: 64 },
+  { key: 'animation', width: 83 },
+  { key: 'container', width: 81 },
+  { key: 'list', width: 35 },
+];
+
+const layout = (available: number, active: string) =>
+  tabRowLayout({ tabs: TABS, available, gap: 2, overflowWidth: 28, active });
+
+describe('tab row', () => {
+  it('hides nothing while the row fits', () => {
+    const { shown, hidden } = layout(631, 'scene');
+    expect(hidden).toEqual([]);
+    expect(shown).toHaveLength(9);
+  });
+
+  it('hides the tail one pixel short of fitting', () => {
+    expect(layout(630, 'scene').hidden).toEqual(['list']);
+  });
+
+  it('keeps the tabs in order', () => {
+    expect(layout(400, 'scene').shown).toEqual(['scene', 'game', 'graph', 'statemachine', 'shader']);
+  });
+
+  it('shows the active tab even when it sits past the room there is', () => {
+    const { shown, hidden } = layout(400, 'container');
+    expect(shown).toContain('container');
+    expect(hidden).toContain('shader');
+    // It went in at the back, so the row still reads left to right.
+    expect(shown[shown.length - 1]).toBe('container');
+  });
+
+  it('gives up every other tab before it drops the active one', () => {
+    expect(layout(60, 'animation')).toEqual({
+      shown: ['animation'],
+      hidden: ['scene', 'game', 'graph', 'statemachine', 'shader', 'texture', 'container', 'list'],
+    });
+  });
+});

tools/e2e/14-overflow.mjs

@@ -6,8 +6,21 @@
 /** A name far wider than any 200 px picker, so a control that does not truncate must spill. */
 const LONG_NAME = 'Player movement with jumping and coyote time';
 
+/** What the tab buttons read, to find one in the overflow menu. */
+const LABELS = {
+  scene: 'Scene',
+  game: 'Game',
+  graph: 'Behavior',
+  statemachine: 'State machine',
+  shader: 'Shader',
+  texture: 'Texture',
+  animation: 'Animation',
+  container: 'Container',
+  list: 'List',
+};
+
 export async function overflow(t) {
-  const { check, sleep, json, evaluate, shot, mutate } = t;
+  const { check, sleep, json, evaluate, shot, mutate, drag, clickText } = t;
 
   const pickerWidths = async () => {
     const out = {};
@@ -42,13 +55,67 @@ export async function overflow(t) {
   //      a click on it lands there (nine tabs on a 90 px floor did exactly that at 1280 px wide).
   await evaluate("__gm.showTab('scene')");
   await sleep(300);
-  const column = await json('__gm.viewportRect()');
+  const columnRight = async () => {
-  const tabs = await json('__gm.tabBounds()');
+    const column = await json('__gm.viewportRect()');
-  const spilled = Object.entries(tabs).filter(([, b]) => b.right > column.x + column.w);
+    return column.x + column.w;
+  };
+  const spillOf = (row, right) => row.shown.filter((b) => b.right > right);
+  const wide = await json('__gm.tabRow()');
   check(
     'every tab button ends inside the centre column',
-    spilled.length === 0,
+    spillOf(wide, await columnRight()).length === 0 && wide.hidden.length === 0,
-    JSON.stringify({ spilled, columnRight: column.x + column.w }),
+    JSON.stringify({ spilled: spillOf(wide, await columnRight()), hidden: wide.hidden }),
+  );
+
+  // 14b-ii. Narrowed until the row cannot hold nine tabs, the leftovers go behind the overflow
+  //         button instead of under the inspector – the guard against the tenth tab (#84).
+  const widenPanels = async (by) => {
+    const bars = await json('__gm.panelSplitters()');
+    await drag(bars.left.x, bars.left.y, bars.left.x + by, bars.left.y, { steps: 8 });
+    const after = await json('__gm.panelSplitters()');
+    await drag(after.right.x, after.right.y, after.right.x - by, after.right.y, { steps: 8 });
+    await sleep(300);
+  };
+  await widenPanels(250);
+  const narrow = await json('__gm.tabRow()');
+  const narrowRight = await columnRight();
+  check(
+    'a row too narrow for its tabs puts the leftovers away instead of past the edge',
+    narrow.hidden.length > 0 && spillOf(narrow, narrowRight).length === 0,
+    JSON.stringify({ hidden: narrow.hidden, spilled: spillOf(narrow, narrowRight) }),
+  );
+  check(
+    'the tab being edited stays in the row',
+    narrow.shown.some((b) => b.tab === 'scene'),
+    JSON.stringify(narrow.shown.map((b) => b.tab)),
+  );
+  await shot('35-tab-overflow');
+  // The overflow button names them, and picking one brings it into the row.
+  const wanted = narrow.hidden[narrow.hidden.length - 1];
+  await clickText('»');
+  await sleep(400);
+  const offered = await json('__gm.overlayTexts()');
+  check(
+    'the overflow button offers every tab that had to go',
+    narrow.hidden.every((tab) => offered.includes(LABELS[tab])),
+    JSON.stringify({ offered, hidden: narrow.hidden }),
+  );
+  await clickText(LABELS[wanted]);
+  await sleep(400);
+  const picked = await json('__gm.tabRow()');
+  check(
+    `picking ${LABELS[wanted]} from the overflow menu opens it and puts it in the row`,
+    (await json('__gm.tab()')) === wanted && picked.shown.some((b) => b.tab === wanted),
+    JSON.stringify({ tab: await json('__gm.tab()'), shown: picked.shown.map((b) => b.tab) }),
+  );
+  await widenPanels(-250);
+  await evaluate("__gm.showTab('scene')");
+  await sleep(300);
+  const back = await json('__gm.tabRow()');
+  check(
+    'giving the room back brings every tab into the row',
+    back.hidden.length === 0 && spillOf(back, await columnRight()).length === 0,
+    JSON.stringify({ hidden: back.hidden }),
   );
 
   // 14c. Every tab, because each one owns a different set of controls.