frontend/src/components/artists-view/artists-view.ts

@@ -10,6 +10,7 @@ import type {
     VisibilityChangedEvent,
 } from '@lit-labs/virtualizer';
 import { grid } from '@lit-labs/virtualizer/layouts/grid.js';
+import { gridSpacingFor } from '@utils/grid-spacing';
 import {
     GetAlbumsByArtist,
     GetFilePathsByAlbums,
@@ -147,8 +148,6 @@ export class ArtistsView
 
     // ----- Grid spacing constants -----
 
-    private static readonly GRID_GAP = 8;
-    private static readonly GRID_PADDING = 8;
     private static readonly CARD_PADDING = 5;
 
     private get imageSize(): number {
@@ -177,20 +176,41 @@ export class ArtistsView
     private createGridLayout() {
         const w = this.cardSize ?? CARD_SIZE_DEFAULT;
         const h = w + this.cardTextHeight;
-        const gap = ArtistsView.GRID_GAP;
-        const pad = ArtistsView.GRID_PADDING;
+
+        // One number for the gap, the row gap and the padding: whatever
+        // a row could not spend on another card, shared out equally, so
+        // the outside is never wider than the inside.  See
+        // `utils/grid-spacing.ts`.
+        const spacing = this.spacingFor(this.containerWidth);
+
+        this.lastLayoutSpacing = spacing;
 
         return grid({
             itemSize: {
                 width: `${w}px`,
                 height: `${h}px`,
             },
-            gap: `${gap}px`,
-            padding: `${pad}px`,
-            justify: 'center',
+            gap: `${spacing}px`,
+            padding: `${spacing}px`,
+            justify: 'start',
         });
     }
 
+    /** The width the grid lays itself out in. */
+    private get containerWidth(): number {
+        return (
+            this.renderRoot?.querySelector<HTMLElement>(
+                '.grid-scroll-container',
+            )?.clientWidth ||
+            this.clientWidth ||
+            0
+        );
+    }
+
+    private spacingFor(width: number): number {
+        return gridSpacingFor(width, this.cardSize);
+    }
+
     /** Sort direction for the artist grid.
      *
      *  There is only one key to sort by: `library.Artist` carries a
@@ -478,6 +498,8 @@ export class ArtistsView
     override disconnectedCallback() {
         super.disconnectedCallback();
         this.detachWheelListener();
+        this.gridResizeObserver?.disconnect();
+        this.gridResizeObserver = null;
     }
 
     /** The wheel listener and the scroll debounce belong to the grid
@@ -730,10 +752,34 @@ export class ArtistsView
      * ================================================================ */
 
     private lastLayoutWidth = 0;
+    private lastLayoutSpacing = 0;
+
+    /** Watches the scroller so a window resize rebuilds the layout:
+     *  the spacing is derived from its width, and nothing else asks
+     *  this view to update when only that changes. */
+    private gridResizeObserver: ResizeObserver | null = null;
+
+    private observeGridWidth() {
+        const container =
+            this.renderRoot?.querySelector<HTMLElement>(
+                '.grid-scroll-container',
+            );
+
+        if (!container || this.gridResizeObserver) return;
+
+        this.gridResizeObserver = new ResizeObserver(() =>
+            this.requestUpdate(),
+        );
+        this.gridResizeObserver.observe(container);
+    }
 
     private updateGridLayout() {
+        this.observeGridWidth();
+
         if (
-            this.cardSize === this.lastLayoutWidth
+            this.cardSize === this.lastLayoutWidth &&
+            this.lastLayoutSpacing ===
+                this.spacingFor(this.containerWidth)
         ) {
             return;
         }

frontend/src/components/cover-grid/cover-grid.ts

@@ -19,6 +19,7 @@ import { LibraryController } from '@store/controllers/library-controller';
 import { SearchController } from '@store/controllers/search-controller';
 import { ViewLifecycleMixin } from '@utils/view-lifecycle';
 import { RovingGridController } from '@utils/roving-grid';
+import { gridColumnsFor, gridSpacingFor } from '@utils/grid-spacing';
 import { queueStore } from '@store/queue-store';
 import type { QueueSource } from '@store/queue-store';
 import '@awesome.me/webawesome/dist/components/popup/popup.js';
@@ -97,19 +98,36 @@ export class CoverGrid
     private lastAlbumsRef: library.Album[] | null =
         null;
 
-    // Fixed grid spacing constants.
-    private static readonly GRID_GAP = 8;
-    private static readonly GRID_PADDING = 8;
     private static readonly CARD_PADDING = 5;
 
     private ctxMenu = new ContextMenuController(this);
     private favCtrl = new FavoritesController(this);
     private selMgr = new AlbumSelectionManager();
     private scrollMgr = new ScrollManager(this, {
-        GRID_GAP: CoverGrid.GRID_GAP,
-        GRID_PADDING: CoverGrid.GRID_PADDING,
+        columnsFor: (width: number) => this.columnsFor(width),
+        spacingFor: (width: number) => this.spacingFor(width),
     });
 
+    /**
+     * How many cards fit across `width`, by the same arithmetic the
+     * virtualizer's `space-evenly` grid uses — no gap and no padding
+     * are reserved, because both come out of what is left over.
+     *
+     * The scroll manager restores a position by rebuilding the grid's
+     * geometry, so this and `spacingFor` must agree with the layout
+     * rather than approximate it; they were two constants that no
+     * longer describe anything once the spacing became elastic.
+     */
+    columnsFor(width: number): number {
+        return gridColumnsFor(width, this.cardWidth);
+    }
+
+    /** The spacing that width produces: between columns, between rows,
+     *  and around the outside, all the same number. */
+    spacingFor(width: number): number {
+        return gridSpacingFor(width, this.cardWidth);
+    }
+
     private lastSelectedAlbumIndex: number | null = null;
     private lastSelectedTrackIndex: number | null = null;
 
@@ -148,10 +166,30 @@ export class CoverGrid
     }
 
     // Virtualizer grid layout instance — recreated when
-    // the card size changes.
+    // the card size or the container width changes.
     private gridLayout = this.createGridLayout();
     private gridLayoutWidth = 0;
 
+    /** The spacing the current layouts were built with. */
+    private gridLayoutSpacing = 0;
+
+    /** Watches the scroll container so a window resize rebuilds the
+     *  layout: the spacing is derived from its width, and nothing else
+     *  asks this component to update when only that changes. */
+    private gridResizeObserver: ResizeObserver | null =
+        null;
+
+    private observeGridWidth(): void {
+        const container = this.scrollContainer;
+
+        if (!container || this.gridResizeObserver) return;
+
+        this.gridResizeObserver = new ResizeObserver(
+            () => this.requestUpdate(),
+        );
+        this.gridResizeObserver.observe(container);
+    }
+
     /**
      * Secondary layout for the "after" virtualizer in
      * split mode.  Uses zero top padding so there is no
@@ -169,22 +207,49 @@ export class CoverGrid
         }
 
         const h = w + this.cardTextHeight;
-        const gap = CoverGrid.GRID_GAP;
-        const pad = CoverGrid.GRID_PADDING;
+
+        // The spacing is whatever the row could not spend on another
+        // card, shared out equally — so it is the same number between
+        // two cards, between two rows, and down each outside edge.
+        // See `utils/grid-spacing.ts` for why it is computed rather
+        // than handed to the virtualizer as `space-evenly`.
+        const spacing = this.spacingFor(
+            this.containerWidth,
+        );
+
+        if (!noTopPad) {
+            this.gridLayoutSpacing = spacing;
+        }
 
         return grid({
             itemSize: {
                 width: `${w}px`,
                 height: `${h}px`,
             },
-            gap: `${gap}px`,
+            gap: `${spacing}px`,
             padding: noTopPad
-                ? `0 ${pad}px ${pad}px`
-                : `${pad}px`,
-            justify: 'center',
+                ? `0 ${spacing}px ${spacing}px`
+                : `${spacing}px`,
+            justify: 'start',
         });
     }
 
+    /**
+     * The width the grid lays itself out in.
+     *
+     * Read from the scroll container when there is one; before the
+     * first render there is not, and the fallback only has to be
+     * plausible — the layout is rebuilt from the real width as soon as
+     * one exists.
+     */
+    private get containerWidth(): number {
+        return (
+            this.scrollContainer?.clientWidth ||
+            this.clientWidth ||
+            0
+        );
+    }
+
     private dragImageEl: HTMLElement | null = null;
 
     // -- Memoisation caches for filtered albums --
@@ -466,6 +531,9 @@ export class CoverGrid
         );
         this.wheelListenerAttached = false;
 
+        this.gridResizeObserver?.disconnect();
+        this.gridResizeObserver = null;
+
         this.scrollMgr.teardown();
         this.scrollMgr.revealContainer(
             this.scrollContainer,
@@ -603,10 +671,18 @@ export class CoverGrid
             this.wheelListenerAttached = true;
         }
 
-        // Recreate the virtualizer grid layout when
-        // the card size changes.
+        this.observeGridWidth();
+
+        // Recreate the virtualizer grid layout when the card size
+        // changes — or when the spacing the container width produces
+        // does, since that is now a derived number rather than a
+        // constant.  Keyed on the spacing rather than on the width, or
+        // every pixel of a drag rebuilds a layout that would come out
+        // the same.
         const cardSizeChanged =
-            this.gridLayoutWidth !== this.cardWidth;
+            this.gridLayoutWidth !== this.cardWidth ||
+            this.gridLayoutSpacing !==
+                this.spacingFor(this.containerWidth);
 
         if (cardSizeChanged) {
             this.gridLayout = this.createGridLayout();

frontend/src/components/cover-grid/scroll-manager.ts

@@ -6,12 +6,21 @@ import type { LibraryController } from '@store/controllers/library-controller';
 import type { GridEntry } from './cover-grid-types.js';
 
 /**
- * Grid spacing constants shared between the scroll
- * manager and the host component.
+ * Grid geometry, asked of the host rather than written down.
+ *
+ * These were two constants, `GRID_GAP` and `GRID_PADDING`, which stopped
+ * describing anything the moment the grid's spacing became elastic: the
+ * gap, the padding and the column count are all derived from the
+ * container width now, and a scroll position rebuilt from a stale 8px
+ * lands in the wrong row.
  */
 export interface GridConstants {
-    readonly GRID_GAP: number;
-    readonly GRID_PADDING: number;
+    /** Columns that fit across `width`. */
+    columnsFor(width: number): number;
+
+    /** The spacing `width` produces — between columns, between rows,
+     *  and around the outside, all the same number. */
+    spacingFor(width: number): number;
 }
 
 /**
@@ -275,8 +284,8 @@ export class ScrollManager {
                 return;
             }
 
-            const gap = this.gc.GRID_GAP;
-            const pad = this.gc.GRID_PADDING;
+            const gap = this.spacing(container);
+            const pad = gap;
             const rowStep =
                 this.host.cardHeight + gap;
 
@@ -293,7 +302,7 @@ export class ScrollManager {
             () => {
                 const rowStep =
                     this.host.cardHeight +
-                    this.gc.GRID_GAP;
+                    this.spacing(container);
 
                 if (this.pendingFocus === null) {
                     this.isResizing = true;
@@ -351,7 +360,7 @@ export class ScrollManager {
         container: HTMLElement,
         rowStep: number,
     ): void {
-        const pad = this.gc.GRID_PADDING;
+        const pad = this.spacing(container);
         const cols = this.currentColumnCount;
         const filtered =
             this.host.cachedFilteredAlbums;
@@ -410,17 +419,15 @@ export class ScrollManager {
     ): number {
         if (!container) return 1;
 
-        const gap = this.gc.GRID_GAP;
-        const pad = this.gc.GRID_PADDING;
-        const availableWidth =
-            container.clientWidth - pad * 2;
+        return this.gc.columnsFor(
+            container.clientWidth,
+        );
+    }
 
-        return Math.max(
-            1,
-            Math.floor(
-                (availableWidth + gap) /
-                    (this.host.cardWidth + gap),
-            ),
+    /** The grid's current spacing, which is also its padding. */
+    private spacing(container?: HTMLElement): number {
+        return this.gc.spacingFor(
+            container?.clientWidth ?? 800,
         );
     }
 
@@ -439,7 +446,7 @@ export class ScrollManager {
         container?: HTMLElement,
     ): number {
         const cols = this.getColumnCount(container);
-        const gap = this.gc.GRID_GAP;
+        const gap = this.spacing(container);
 
         return (
             cols * this.host.cardWidth +
@@ -460,7 +467,7 @@ export class ScrollManager {
 
         const cols = this.getColumnCount(container);
         const colIndex = idx % cols;
-        const gap = this.gc.GRID_GAP;
+        const gap = this.spacing(container);
 
         return (
             colIndex *
@@ -597,8 +604,8 @@ export class ScrollManager {
 
         if (!this.host.splitMode) return raw;
 
-        const gap = this.gc.GRID_GAP;
-        const pad = this.gc.GRID_PADDING;
+        const gap = this.spacing(container);
+        const pad = gap;
         const columns =
             this.getColumnCount(container);
         const rowStep = this.host.cardHeight + gap;
@@ -678,8 +685,8 @@ export class ScrollManager {
 
         if (expandedIndex < 0) return;
 
-        const gap = this.gc.GRID_GAP;
-        const pad = this.gc.GRID_PADDING;
+        const gap = this.spacing(container);
+        const pad = gap;
         const columns =
             this.getColumnCount(container);
         const rowStep = this.host.cardHeight + gap;
@@ -772,8 +779,8 @@ export class ScrollManager {
 
         if (idx < 0) return;
 
-        const gap = this.gc.GRID_GAP;
-        const pad = this.gc.GRID_PADDING;
+        const gap = this.spacing(container);
+        const pad = gap;
         const cols =
             this.getColumnCount(container);
         const rowStep = this.host.cardHeight + gap;
@@ -854,9 +861,8 @@ export class ScrollManager {
                         this.getExpandedAlbumIndex();
 
                     if (idx >= 0) {
-                        const gap = this.gc.GRID_GAP;
-                        const pad =
-                            this.gc.GRID_PADDING;
+                        const gap = this.spacing(container);
+                        const pad = gap;
                         const cols =
                             this.getColumnCount(
                                 container,

frontend/src/components/genres-view/genres-view.ts

@@ -10,6 +10,7 @@ import type {
     VisibilityChangedEvent,
 } from '@lit-labs/virtualizer';
 import { grid } from '@lit-labs/virtualizer/layouts/grid.js';
+import { gridSpacingFor } from '@utils/grid-spacing';
 import {
     GetFilePathsByGenres,
 } from '@go/library/library.js';
@@ -155,8 +156,6 @@ export class GenresView
 
     // ----- Grid spacing constants -----
 
-    private static readonly GRID_GAP = 8;
-    private static readonly GRID_PADDING = 8;
     private static readonly CARD_PADDING = 5;
 
     private get imageSize(): number {
@@ -185,20 +184,41 @@ export class GenresView
     private createGridLayout() {
         const w = this.cardSize ?? CARD_SIZE_DEFAULT;
         const h = w + this.cardTextHeight;
-        const gap = GenresView.GRID_GAP;
-        const pad = GenresView.GRID_PADDING;
+
+        // One number for the gap, the row gap and the padding: whatever
+        // a row could not spend on another card, shared out equally, so
+        // the outside is never wider than the inside.  See
+        // `utils/grid-spacing.ts`.
+        const spacing = this.spacingFor(this.containerWidth);
+
+        this.lastLayoutSpacing = spacing;
 
         return grid({
             itemSize: {
                 width: `${w}px`,
                 height: `${h}px`,
             },
-            gap: `${gap}px`,
-            padding: `${pad}px`,
-            justify: 'center',
+            gap: `${spacing}px`,
+            padding: `${spacing}px`,
+            justify: 'start',
         });
     }
 
+    /** The width the grid lays itself out in. */
+    private get containerWidth(): number {
+        return (
+            this.renderRoot?.querySelector<HTMLElement>(
+                '.grid-scroll-container',
+            )?.clientWidth ||
+            this.clientWidth ||
+            0
+        );
+    }
+
+    private spacingFor(width: number): number {
+        return gridSpacingFor(width, this.cardSize);
+    }
+
     /** Sort key and direction for the genre grid (H-19: it had none). */
     @state()
     private sortField: 'name' | 'tracks' = 'name';
@@ -483,6 +503,8 @@ export class GenresView
     override disconnectedCallback() {
         super.disconnectedCallback();
         this.detachWheelListener();
+        this.gridResizeObserver?.disconnect();
+        this.gridResizeObserver = null;
     }
 
     /** See artists-view: off-screen the grid cannot be scrolled, and
@@ -737,10 +759,34 @@ export class GenresView
      * ================================================================ */
 
     private lastLayoutWidth = 0;
+    private lastLayoutSpacing = 0;
+
+    /** Watches the scroller so a window resize rebuilds the layout:
+     *  the spacing is derived from its width, and nothing else asks
+     *  this view to update when only that changes. */
+    private gridResizeObserver: ResizeObserver | null = null;
+
+    private observeGridWidth() {
+        const container =
+            this.renderRoot?.querySelector<HTMLElement>(
+                '.grid-scroll-container',
+            );
+
+        if (!container || this.gridResizeObserver) return;
+
+        this.gridResizeObserver = new ResizeObserver(() =>
+            this.requestUpdate(),
+        );
+        this.gridResizeObserver.observe(container);
+    }
 
     private updateGridLayout() {
+        this.observeGridWidth();
+
         if (
-            this.cardSize === this.lastLayoutWidth
+            this.cardSize === this.lastLayoutWidth &&
+            this.lastLayoutSpacing ===
+                this.spacingFor(this.containerWidth)
         ) {
             return;
         }

frontend/src/utils/grid-spacing.ts

@@ -0,0 +1,58 @@
+/**
+ * Even spacing for the three card grids — albums, artists, genres.
+ *
+ * All three used `justify: 'center'` with a fixed 8px gap and 8px
+ * padding, which gives the row a fixed width and pushes everything left
+ * over to the two margins: on a 1440px window the albums grid drew its
+ * cards 16px apart inside 78px of nothing down each side. The outside
+ * was five times the inside.
+ *
+ * The fix is to spend the leftover on the spacing instead, so there is
+ * one number: between two cards, between two rows, and down each edge.
+ * The virtualizer has a word for that — `justify: 'space-evenly'` with
+ * `gap: 'auto'` — and it cannot be used, because it fits
+ * `floor(width / cardWidth)` columns without reserving the gap it is
+ * about to need: a width one card short of exact fits seven cards a
+ * pixel apart. Deciding the column count here is what puts a floor
+ * under the spacing, and the grid is then given plain numbers.
+ */
+
+/** The narrowest the spacing is allowed to get. */
+export const MIN_GRID_SPACING = 8;
+
+/**
+ * How many cards of `cardWidth` fit across `width`.
+ *
+ * A row of c cards spends c×cardWidth on cards and (c+1)×spacing on the
+ * spaces between and beside them, so c is bounded by
+ * (width − spacing) / (cardWidth + spacing) at the minimum spacing.
+ */
+export function gridColumnsFor(
+    width: number,
+    cardWidth: number,
+): number {
+    if (cardWidth <= 0) return 1;
+
+    const fit = Math.floor(
+        (width - MIN_GRID_SPACING) / (cardWidth + MIN_GRID_SPACING),
+    );
+
+    return Math.max(1, fit);
+}
+
+/**
+ * The spacing `width` produces — the gap, the row gap and the padding,
+ * which are all the same number.
+ */
+export function gridSpacingFor(
+    width: number,
+    cardWidth: number,
+): number {
+    const columns = gridColumnsFor(width, cardWidth);
+    const leftover = width - columns * cardWidth;
+
+    return Math.max(
+        MIN_GRID_SPACING,
+        Math.floor(leftover / (columns + 1)),
+    );
+}