feat(backgrounds): add snowfall background

src/components/ui/backgrounds/registry.ts

@@ -19,6 +19,7 @@ const backgroundImports: Record<Exclude<BackgroundType, 'none'>, () => Promise<u
   spotlight: () => import('./spotlight-bg'),
   ripple: () => import('./background-ripple'),
   fireflies: () => import('./fireflies'),
+  snowfall: () => import('./snowfall'),
 };
 
 /** Prefetch the JS chunk for a background type (call early to avoid lazy-load delay) */
@@ -49,6 +50,7 @@ export const backgroundComponents: Record<
   spotlight: lazy(() => import('./spotlight-bg')),
   ripple: lazy(() => import('./background-ripple')),
   fireflies: lazy(() => import('./fireflies')),
+  snowfall: lazy(() => import('./snowfall')),
 };
 
 // Registry of all background definitions with settings for the editor
@@ -616,4 +618,40 @@ export const backgroundRegistry: BackgroundDefinition[] = [
       },
     ],
   },
+  {
+    type: 'snowfall',
+    labelKey: 'admin.backgrounds.snowfall',
+    descriptionKey: 'admin.backgrounds.snowfallDesc',
+    category: 'canvas',
+    settings: [
+      { key: 'color', label: 'admin.backgrounds.particleColor', type: 'color', default: '#ffffff' },
+      {
+        key: 'density',
+        label: 'admin.backgrounds.density',
+        type: 'number',
+        min: 20,
+        max: 400,
+        step: 10,
+        default: 150,
+      },
+      {
+        key: 'speed',
+        label: 'admin.backgrounds.speed',
+        type: 'number',
+        min: 0.1,
+        max: 3,
+        step: 0.1,
+        default: 1,
+      },
+      {
+        key: 'wind',
+        label: 'admin.backgrounds.wind',
+        type: 'number',
+        min: -3,
+        max: 3,
+        step: 0.5,
+        default: 0.5,
+      },
+    ],
+  },
 ];

src/components/ui/backgrounds/snowfall.tsx

@@ -0,0 +1,114 @@
+import { useEffect, useRef } from 'react';
+import { sanitizeColor, clampNumber } from './types';
+import { useAnimationLoop, getMobileDpr } from '@/hooks/useAnimationLoop';
+
+interface Props {
+  settings: Record<string, unknown>;
+}
+
+interface Flake {
+  x: number;
+  y: number;
+  radius: number;
+  fallSpeed: number;
+  phase: number;
+  opacity: number;
+}
+
+interface SnowfallState {
+  ctx: CanvasRenderingContext2D;
+  flakes: Flake[];
+  w: number;
+  h: number;
+  dpr: number;
+}
+
+export default function SnowfallBackground({ settings }: Props) {
+  const canvasRef = useRef<HTMLCanvasElement>(null);
+  const stateRef = useRef<SnowfallState | null>(null);
+
+  const color = sanitizeColor(settings.color, '#ffffff');
+  const density = clampNumber(settings.density, 20, 400, 150);
+  const speed = clampNumber(settings.speed, 0.1, 3, 1);
+  const wind = clampNumber(settings.wind, -3, 3, 0.5);
+
+  useEffect(() => {
+    const canvas = canvasRef.current;
+    if (!canvas) return;
+
+    const dpr = getMobileDpr();
+    const parent = canvas.parentElement;
+    const w = parent?.offsetWidth ?? window.innerWidth;
+    const h = parent?.offsetHeight ?? window.innerHeight;
+    canvas.width = w * dpr;
+    canvas.height = h * dpr;
+    canvas.style.width = `${w}px`;
+    canvas.style.height = `${h}px`;
+
+    const ctx = canvas.getContext('2d');
+    if (!ctx) return;
+    ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
+
+    const flakes: Flake[] = Array.from({ length: Math.floor(density) }, () => ({
+      x: Math.random() * w,
+      y: Math.random() * h,
+      radius: 0.8 + Math.random() * 2.2,
+      fallSpeed: 0.4 + Math.random() * 1.2,
+      phase: Math.random() * Math.PI * 2,
+      opacity: 0.3 + Math.random() * 0.7,
+    }));
+
+    stateRef.current = { ctx, flakes, w, h, dpr };
+
+    const onResize = () => {
+      const nw = parent?.offsetWidth ?? window.innerWidth;
+      const nh = parent?.offsetHeight ?? window.innerHeight;
+      canvas.width = nw * dpr;
+      canvas.height = nh * dpr;
+      canvas.style.width = `${nw}px`;
+      canvas.style.height = `${nh}px`;
+      if (stateRef.current) {
+        stateRef.current.ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
+        stateRef.current.w = nw;
+        stateRef.current.h = nh;
+      }
+    };
+
+    window.addEventListener('resize', onResize);
+    return () => window.removeEventListener('resize', onResize);
+  }, [density]);
+
+  useAnimationLoop(
+    (time) => {
+      const state = stateRef.current;
+      if (!state) return;
+
+      const { ctx, flakes, w, h } = state;
+
+      ctx.clearRect(0, 0, w, h);
+      ctx.fillStyle = color;
+
+      for (const f of flakes) {
+        f.y += f.fallSpeed * speed;
+        f.x += wind * f.fallSpeed * 0.6 + Math.sin(time / 1800 + f.phase) * 0.4;
+
+        if (f.y > h + 5) {
+          f.y = -5;
+          f.x = Math.random() * w;
+        }
+        if (f.x > w + 5) f.x = -5;
+        if (f.x < -5) f.x = w + 5;
+
+        ctx.globalAlpha = f.opacity;
+        ctx.beginPath();
+        ctx.arc(f.x, f.y, f.radius, 0, Math.PI * 2);
+        ctx.fill();
+      }
+
+      ctx.globalAlpha = 1;
+    },
+    [color, density, speed, wind],
+  );
+
+  return <canvas ref={canvasRef} className="absolute inset-0 h-full w-full" />;
+}

src/components/ui/backgrounds/types.ts

@@ -15,6 +15,7 @@ export type BackgroundType =
   | 'spotlight'
   | 'ripple'
   | 'fireflies'
+  | 'snowfall'
   | 'none';
 
 export interface AnimationConfig {