some more features and fixes (title and show info)

frontend/js/marquee.js

@@ -0,0 +1,51 @@
+window.App = window.App || {};
+App.marquee = App.marquee || {};
+
+// A title is always one line. When it doesn't fit its box it scrolls sideways
+// instead of wrapping or being silently cut off.
+//
+// Four surfaces show a title that way -- the grid card, the favorites bar card,
+// the fullscreen player, the reels slide -- and they must scroll at the same
+// speed to look like one app, so the measurement lives here rather than being
+// written out again next to each of them. Whether a given title is *currently*
+// scrolling is the caller's business (see the `is-title-active` handling in
+// videos.js and favorites.js): a whole grid of marching text is unreadable, so
+// most callers animate only the title the reader is actually looking at.
+(function() {
+    // Drive the duration off the distance so every title scrolls at the same
+    // gentle rate rather than a fixed duration, which made longer titles whip
+    // past. The floor keeps short ones from snapping.
+    const SPEED_PX_PER_SEC = 28;
+    const MIN_DURATION_S = 6;
+    // Sub-pixel rounding isn't overflow worth animating.
+    const OVERFLOW_SLACK_PX = 4;
+    // Trailing space so the last word clears the edge before it wraps around.
+    const TAIL_GAP_PX = 12;
+
+    // Measures `text` inside `wrap` and prepares the animation: sets
+    // --marquee-distance / --marquee-duration on `text`, and marks `wrap` with
+    // `has-marquee` so CSS can decide what to do about it. Returns whether the
+    // title overflows -- callers use that to skip the bookkeeping (scroll
+    // observers, hover handlers) that only scrolling titles need.
+    //
+    // Reads layout, so call it when the element is in the document and visible;
+    // a hidden element measures as zero-width and reports no overflow.
+    App.marquee.measure = function(wrap, text) {
+        if (!wrap || !text) return false;
+
+        const overflow = text.scrollWidth - wrap.clientWidth;
+        if (overflow <= OVERFLOW_SLACK_PX) {
+            wrap.classList.remove('has-marquee');
+            text.style.removeProperty('--marquee-distance');
+            text.style.removeProperty('--marquee-duration');
+            return false;
+        }
+
+        const distance = overflow + TAIL_GAP_PX;
+        const duration = Math.max(MIN_DURATION_S, distance / SPEED_PX_PER_SEC);
+        text.style.setProperty('--marquee-distance', `${distance}px`);
+        text.style.setProperty('--marquee-duration', `${duration.toFixed(2)}s`);
+        wrap.classList.add('has-marquee');
+        return true;
+    };
+})();