perf(grid): improve layout responsiveness and remove selection transitions (#2400)

This PR addresses performance issues in the media grid by disabling
resource-intensive CSS transitions and ensuring immediate layout
updates. Previously, the default `0.2s` transition duration for grid
reshuffling was causing browser overloads on devices with multiple live
video viewers, leading to stuttering and occasionally missing
short-lived video events.

## Changes

### 1. Disable Masonry Transitions
- Set `transitionDuration` to `0` in the Masonry configuration to
eliminate CSS-driven animations during layout.
- Set `stagger` to `0` to ensure all items move simultaneously and
instantly.
- Set `resize` to `false` in the Masonry config, as window resizing is
already efficiently handled by the controller's `ResizeObserver`.

### 2. Immediate Layout Updates
- Introduced a `_forceLayout()` method in `MediaGridController` that:
- Cancels any pending throttled layout calls to avoid redundant work.
- Triggers a browser reflow via `getBoundingClientRect()` to ensure all
element dimensions are synchronized before the next draw.
    - Forces an immediate Masonry layout.
- Integrated `_forceLayout()` into `selectCell()` and `unselectAll()` to
guarantee the grid updates at the exact moment a user interacts with it.

### 3. Test Alignment
- Updated `tests/components-lib/media-grid-controller.test.ts` to
reflect the changes.

## Performance Impact
By eliminating timed transitions, we significantly reduce the peak CPU
and GPU load during grid selection changes. This results in a much
snappier UI where video viewers snap into position instantly, preventing
the "shuttering" effect and ensuring that time-critical video playback
is not interrupted by heavy animation cycles.

---------

Co-authored-by: dermotduffy <dermot.duffy@gmail.com>

src/components-lib/media-grid-controller.ts

@@ -3,6 +3,7 @@ import Masonry from 'masonry-layout';
 import { ViewDisplayConfig } from '../config/schema/common/display';
 import { MediaLoadedInfo } from '../types';
 import {
+  forceReflow,
   getChildrenFromElement,
   setOrRemoveAttribute,
   setOrRemoveStyleProperty,
@@ -58,13 +59,10 @@ export class MediaGridController {
   private _idAttribute: string;
   private _widthFactorAttribute: string;
 
-  private _throttledLayout = throttle(
-    () => this._masonry?.layout?.(),
-    // Throttle layout calls to larger than the masonry.js transitionDuration
-    // value specified below.
-    300,
-    { trailing: true, leading: false },
-  );
+  private _throttledLayout = throttle(() => this._masonry?.layout?.(), 300, {
+    leading: true,
+    trailing: true,
+  });
 
   // If the order in which the observers are declared changes, the unittest must
   // be updated in triggerResizeObserver and triggerMutationObserver.
@@ -186,10 +184,7 @@ export class MediaGridController {
     this._sortItemsInGrid();
     this._updateSelectedStylesOnElements();
 
-    // Sizes and positions may change when an element is selected, so re-do the
-    // layout (must come after the call to _updateStylesOnElements in order to
-    // ensure the right styles are applied first).
-    this._throttledLayout();
+    this._forceLayout();
   }
 
   public unselectAll() {
@@ -199,6 +194,19 @@ export class MediaGridController {
     }
     this._selected = null;
     this._updateSelectedStylesOnElements();
+
+    this._forceLayout();
+  }
+
+  protected _forceLayout(): void {
+    // Cancel possible pending layout
+    this._throttledLayout.cancel();
+
+    // Force browser reflow so masonry measures the updated element size
+    forceReflow(this._host);
+
+    // Sizes and positions may change when an element is selected, so re-do the layout
+    this._masonry?.layout?.();
   }
 
   private _calculateGridContentsFromHost = (): void => {
@@ -318,7 +326,11 @@ export class MediaGridController {
       columnWidth: this._getColumnSize(),
       initLayout: false,
       percentPosition: true,
-      transitionDuration: '0.2s',
+      transitionDuration: 0,
+      stagger: 0,
+
+      // This controller handles resizes.
+      resize: false,
       gutter: MEDIA_GRID_HORIZONTAL_GUTTER_WIDTH,
     }) as ExtendedMasonry;
     this._masonry.addItems?.([...this._gridContents.values()]);

tests/components-lib/media-grid-controller.test.ts

@@ -17,7 +17,11 @@ import {
 
 vi.mock('lodash-es', async () => ({
   ...(await vi.importActual('lodash-es')),
-  throttle: vi.fn((fn) => fn),
+  throttle: vi.fn((fn) => {
+    const throttled = vi.fn(fn) as unknown as { cancel: () => void };
+    throttled.cancel = vi.fn();
+    return throttled;
+  }),
 }));
 
 const masonry = mock<ExtendedMasonry>();
@@ -394,7 +398,7 @@ describe('MediaGridController', () => {
       expect.objectContaining({
         initLayout: false,
         percentPosition: true,
-        transitionDuration: '0.2s',
+        transitionDuration: 0,
       }),
     );
   });