perf: frame-rate independent animation + Scroll-Driven progress bar

- MatrixRain: add delta time for consistent speed across 60/120/144Hz displays
- ReadingProgress: use Scroll-Driven Animations API with JS fallback
- Fallback to scroll events for unsupported browsers (Firefox) and prefers-reduced-motion

Co-authored-by: Cursor <cursoragent@cursor.com>

components/matrix-rain.tsx

@@ -58,9 +58,14 @@ export function MatrixRain({
     }));
 
     let animationId: number;
+    let lastTime: number | null = null;
 
-    const draw = () => {
+    const draw = (timestamp: number) => {
       const rect = canvas.getBoundingClientRect();
+      const delta =
+        lastTime !== null ? (timestamp - lastTime) / 1000 : 1 / 60;
+      lastTime = timestamp;
+
       ctx.fillStyle = 'rgba(15, 23, 42, 0.05)';
       ctx.fillRect(0, 0, rect.width, rect.height);
 
@@ -83,7 +88,8 @@ export function MatrixRain({
           );
         }
 
-        drop.y += drop.speed * fontSize;
+        // Frame-rate independent: scale by delta, 60fps as baseline
+        drop.y += drop.speed * fontSize * delta * 60;
         if (drop.y > rect.height + 100) {
           drop.y = -50;
           drop.charIndex = (drop.charIndex + 1) % 20;
@@ -95,7 +101,7 @@ export function MatrixRain({
       animationId = requestAnimationFrame(draw);
     };
 
-    draw();
+    animationId = requestAnimationFrame(draw);
 
     return () => {
       cancelAnimationFrame(animationId);

components/reading-progress.tsx

@@ -3,16 +3,34 @@
 import { useEffect, useState } from 'react';
 import { createPortal } from 'react-dom';
 
+function supportsScrollDrivenAnimations(): boolean {
+  if (typeof CSS === 'undefined') return false;
+  return CSS.supports?.('animation-timeline', 'scroll()') ?? false;
+}
+
 export function ReadingProgress() {
   const [mounted, setMounted] = useState(false);
   const [progress, setProgress] = useState(0);
+  const [useScrollDriven, setUseScrollDriven] = useState(false);
 
   useEffect(() => {
     setMounted(true);
+    const updateMode = () => {
+      const prefersReducedMotion = window.matchMedia(
+        '(prefers-reduced-motion: reduce)'
+      ).matches;
+      setUseScrollDriven(
+        supportsScrollDrivenAnimations() && !prefersReducedMotion
+      );
+    };
+    updateMode();
+    const mq = window.matchMedia('(prefers-reduced-motion: reduce)');
+    mq.addEventListener('change', updateMode);
+    return () => mq.removeEventListener('change', updateMode);
   }, []);
 
   useEffect(() => {
-    if (!mounted) return;
+    if (!mounted || useScrollDriven) return;
 
     const handleScroll = () => {
       const { scrollTop, scrollHeight, clientHeight } = document.documentElement;
@@ -28,21 +46,38 @@ export function ReadingProgress() {
     handleScroll();
     window.addEventListener('scroll', handleScroll, { passive: true });
     return () => window.removeEventListener('scroll', handleScroll);
-  }, [mounted]);
-
+  }, [mounted, useScrollDriven]);
 
   if (!mounted) return null;
 
   return createPortal(
     <div className="pointer-events-none fixed inset-x-0 top-0 z-[1200] h-1.5 bg-transparent">
       <div className="relative h-1.5 w-full overflow-visible">
-        <div
-          className="absolute inset-y-0 left-0 w-full origin-left rounded-full bg-gradient-to-r from-[rgba(124,58,237,0.9)] via-[rgba(167,139,250,0.9)] to-[rgba(14,165,233,0.8)] shadow-[0_0_12px_rgba(124,58,237,0.5)] transition-[transform,opacity] duration-300 ease-out"
-          style={{ transform: `scaleX(${progress / 100})`, opacity: progress > 0 ? 1 : 0 }}
-        >
-          <span className="absolute -right-2 top-1/2 h-3 w-3 -translate-y-1/2 rounded-full bg-white/80 blur-[1px] dark:bg-slate-900/80" aria-hidden="true" />
-        </div>
-        <span className="absolute inset-x-0 top-2 h-px bg-gradient-to-r from-transparent via-blue-200/40 to-transparent blur-sm dark:via-blue-900/30" aria-hidden="true" />
+        {useScrollDriven ? (
+          <div className="reading-progress-bar-scroll-driven absolute inset-y-0 left-0 w-full origin-left rounded-full bg-gradient-to-r from-[rgba(124,58,237,0.9)] via-[rgba(167,139,250,0.9)] to-[rgba(14,165,233,0.8)] shadow-[0_0_12px_rgba(124,58,237,0.5)]">
+            <span
+              className="absolute -right-2 top-1/2 h-3 w-3 -translate-y-1/2 rounded-full bg-white/80 blur-[1px] dark:bg-slate-900/80"
+              aria-hidden="true"
+            />
+          </div>
+        ) : (
+          <div
+            className="absolute inset-y-0 left-0 w-full origin-left rounded-full bg-gradient-to-r from-[rgba(124,58,237,0.9)] via-[rgba(167,139,250,0.9)] to-[rgba(14,165,233,0.8)] shadow-[0_0_12px_rgba(124,58,237,0.5)] transition-[transform,opacity] duration-300 ease-out"
+            style={{
+              transform: `scaleX(${progress / 100})`,
+              opacity: progress > 0 ? 1 : 0
+            }}
+          >
+            <span
+              className="absolute -right-2 top-1/2 h-3 w-3 -translate-y-1/2 rounded-full bg-white/80 blur-[1px] dark:bg-slate-900/80"
+              aria-hidden="true"
+            />
+          </div>
+        )}
+        <span
+          className="absolute inset-x-0 top-2 h-px bg-gradient-to-r from-transparent via-blue-200/40 to-transparent blur-sm dark:via-blue-900/30"
+          aria-hidden="true"
+        />
       </div>
     </div>,
     document.body

styles/globals.css

@@ -97,6 +97,17 @@
   }
 }
 
+/* Reading progress bar - Scroll-Driven Animations API (Chrome 115+, Safari 26+, Edge 115+) */
+@keyframes reading-progress-grow {
+  from { transform: scaleX(0); }
+  to { transform: scaleX(1); }
+}
+
+.reading-progress-bar-scroll-driven {
+  animation: reading-progress-grow auto linear forwards;
+  animation-timeline: scroll(block root);
+}
+
 :root {
   --motion-duration-short: 180ms;
   --motion-duration-medium: 260ms;