src/app/ui/Layout.svelte

@@ -49,8 +49,6 @@ onMount(async () => {
     }
     fontsReady = true;
 });
-
-$inspect(fontsReady);
 </script>
 
 <svelte:head>

src/entities/Font/model/store/appliedFontsStore/appliedFontsStore.svelte.ts

@@ -112,7 +112,7 @@ export class AppliedFontsManager {
             const internalName = `f_${config.id}`;
             const weightRange = config.isVariable ? '100 900' : `${config.weight}`;
 
-            const font = new FontFace(config.name, `url(${config.url})`, {
+            const font = new FontFace(config.name, `url(${config.url}) format('woff2')`, {
                 weight: weightRange,
                 style: 'normal',
                 display: 'swap',

src/entities/Font/ui/FontApplicator/FontApplicator.svelte

@@ -6,30 +6,24 @@
     - Adds smooth transition when font appears
 -->
 <script lang="ts">
+import { getFontUrl } from '$entities/Font/lib';
 import { cn } from '$shared/shadcn/utils/shadcn-utils';
 import type { Snippet } from 'svelte';
 import { prefersReducedMotion } from 'svelte/motion';
-import { appliedFontsManager } from '../../model';
+import {
+    type UnifiedFont,
+    appliedFontsManager,
+} from '../../model';
 
 interface Props {
     /**
-     * Font name to set
+     * Applied font
      */
-    name: string;
+    font: UnifiedFont;
-    /**
-     * Font id to load
-     */
-    id: string;
-    /** */
-    url: string;
     /**
      * Font weight
      */
     weight?: number;
-    /**
-     * Variable font flag
-     */
-    isVariable?: boolean;
     /**
      * Additional classes
      */
@@ -40,12 +34,12 @@ interface Props {
     children?: Snippet;
 }
 
-let { name, id, url, weight = 400, isVariable = false, className, children }: Props = $props();
+let { font, weight = 400, className, children }: Props = $props();
 let element: Element;
 
 // Track if the user has actually scrolled this into view
 let hasEnteredViewport = $state(false);
-const status = $derived(appliedFontsManager.getFontStatus(id, weight, isVariable));
+const status = $derived(appliedFontsManager.getFontStatus(font.id, weight, font.features.isVariable));
 
 $effect(() => {
     if (status === 'loaded' || status === 'error') {
@@ -56,17 +50,19 @@ $effect(() => {
     const observer = new IntersectionObserver(entries => {
         if (entries[0].isIntersecting) {
             hasEnteredViewport = true;
-
+            const url = getFontUrl(font, weight);
             // Touch ensures it's in the queue.
             // It's safe to call this even if VirtualList called it
             // (Manager dedupes based on key)
+            if (url) {
                 appliedFontsManager.touch([{
-                id,
+                    id: font.id,
                     weight,
-                name,
+                    name: font.name,
                     url,
-                isVariable,
+                    isVariable: font.features.isVariable,
                 }]);
+            }
 
             observer.unobserve(element);
         }
@@ -88,7 +84,7 @@ const transitionClasses = $derived(
 
 <div
     bind:this={element}
-    style:font-family={shouldReveal ? `'${name}'` : 'system-ui, -apple-system, sans-serif'}
+    style:font-family={shouldReveal ? `'${font.name}'` : 'system-ui, -apple-system, sans-serif'}
     class={cn(
         transitionClasses,
         // If reduced motion is on, we skip the transform/blur entirely

src/features/DisplayFont/ui/FontSampler/FontSampler.svelte

@@ -84,8 +84,7 @@ const letterSpacing = $derived(controlManager.spacing);
     </div>
 
     <div class="p-4 sm:p-5 md:p-8 relative z-10">
-        <!-- TODO: Fix this ! -->
+        <FontApplicator {font} weight={fontWeight}>
-        <FontApplicator id={font.id} name={font.name} url={font.styles.regular!}>
             <ContentEditable
                 bind:text={text}
                 {...restProps}

src/shared/ui/ComboControlV2/ComboControlV2.svelte

@@ -109,7 +109,7 @@ function calculateScale(index: number): number | string {
 {#snippet ComboControl()}
     <div
         class={cn(
-            'flex gap-4 sm:p-4 rounded-xl transition-all duration-300',
+            'flex gap-4 sm:py-4 sm:px-1 rounded-xl transition-all duration-300',
             'backdrop-blur-md',
             orientation === 'horizontal' ? 'flex-row items-end w-full' : 'flex-col items-center h-full',
             className,

src/shared/ui/ExpandableWrapper/ExpandableWrapper.svelte

@@ -3,6 +3,7 @@
     Animated wrapper for content that can be expanded and collapsed.
 -->
 <script lang="ts">
+import { debounce } from '$shared/lib/utils';
 import { cn } from '$shared/shadcn/utils/shadcn-utils';
 import type { Snippet } from 'svelte';
 import { cubicOut } from 'svelte/easing';
@@ -38,6 +39,10 @@ interface Props extends HTMLAttributes<HTMLDivElement> {
      * Optional badge to render
      */
     badge?: Snippet<[{ expanded?: boolean; disabled?: boolean }]>;
+    /**
+     * Callback for when the element's size changes
+     */
+    onResize?: (rect: DOMRectReadOnly) => void;
     /**
      * Rotation animation direction
      * @default 'clockwise'
@@ -56,6 +61,7 @@ let {
     visibleContent,
     hiddenContent,
     badge,
+    onResize,
     rotation = 'clockwise',
     class: className = '',
     containerClassName = '',
@@ -64,7 +70,7 @@ let {
 
 let timeoutId = $state<ReturnType<typeof setTimeout> | null>(null);
 
-export const xSpring = new Spring(0, {
+const xSpring = new Spring(0, {
     stiffness: 0.14, // Lower is slower
     damping: 0.5, // Settle
 });
@@ -79,7 +85,7 @@ const scaleSpring = new Spring(1, {
     damping: 0.65,
 });
 
-export const rotateSpring = new Spring(0, {
+const rotateSpring = new Spring(0, {
     stiffness: 0.12,
     damping: 0.55,
 });
@@ -107,6 +113,9 @@ function handleKeyDown(e: KeyboardEvent) {
     }
 }
 
+// Create debounced recize callback
+const debouncedResize = debounce((entry: ResizeObserverEntry) => onResize?.(entry.contentRect), 50);
+
 // Elevation and scale on activation
 $effect(() => {
     if (expanded && !disabled) {
@@ -149,6 +158,21 @@ $effect(() => {
         expanded = false;
     }
 });
+
+// Use an effect to watch the element's actual physical size
+$effect(() => {
+    if (!element) return;
+
+    const observer = new ResizeObserver(entries => {
+        const entry = entries[0];
+        if (entry) {
+            debouncedResize(entry);
+        }
+    });
+
+    observer.observe(element);
+    return () => observer.disconnect();
+});
 </script>
 
 <div
@@ -158,7 +182,7 @@ $effect(() => {
     role="button"
     tabindex={0}
     class={cn(
-        'will-change-transform duration-300',
+        'will-change-[transform, width, height] duration-300',
         disabled ? 'pointer-events-none' : 'pointer-events-auto',
         className,
     )}

src/widgets/ComparisonSlider/model/stores/comparisonStore.svelte.ts

@@ -34,6 +34,7 @@ class ComparisonStore {
     #fontB = $state<UnifiedFont | undefined>();
     #sampleText = $state('The quick brown fox jumps over the lazy dog');
     #isRestoring = $state(true);
+    #fontsReady = $state(false);
     #typography = createTypographyControlManager(DEFAULT_TYPOGRAPHY_CONTROLS_DATA, 'glyphdiff:comparison:typography');
 
     constructor() {
@@ -49,6 +50,7 @@ class ComparisonStore {
 
                 // If we already have a selection, do nothing
                 if (this.#fontA && this.#fontB) {
+                    this.#checkFontsLoaded();
                     return;
                 }
 
@@ -66,6 +68,48 @@ class ComparisonStore {
         });
     }
 
+    /**
+     * Checks if fonts are actually loaded in the browser at current weight.
+     * Uses CSS Font Loading API to prevent FOUT.
+     */
+    async #checkFontsLoaded() {
+        if (!('fonts' in document)) {
+            this.#fontsReady = true;
+            return;
+        }
+
+        this.#fontsReady = false;
+
+        const weight = this.#typography.weight;
+        const size = this.#typography.renderedSize;
+        const fontAName = this.#fontA?.name;
+        const fontBName = this.#fontB?.name;
+
+        if (!fontAName || !fontBName) return;
+
+        try {
+            // Step 1: Load fonts into memory
+            await Promise.all([
+                document.fonts.load(`${weight} ${size}px "${fontAName}"`),
+                document.fonts.load(`${weight} ${size}px "${fontBName}"`),
+            ]);
+
+            // Step 2: Wait for browser to be ready to render
+            await document.fonts.ready;
+
+            // Step 3: Force a layout/paint cycle (critical!)
+            await new Promise(resolve => {
+                requestAnimationFrame(() => {
+                    requestAnimationFrame(resolve); // Double rAF ensures paint completes
+                });
+            });
+
+            this.#fontsReady = true;
+        } catch (error) {
+            console.warn('[ComparisonStore] Font loading failed:', error);
+            setTimeout(() => this.#fontsReady = true, 1000);
+        }
+    }
     /**
      * Restore state from persistent storage
      */
@@ -141,13 +185,12 @@ class ComparisonStore {
      * Check if both fonts are selected
      */
     get isReady() {
-        return !!this.#fontA && !!this.#fontB;
+        return !!this.#fontA && !!this.#fontB && this.#fontsReady;
     }
 
     get isLoading() {
-        return this.#isRestoring;
+        return this.#isRestoring || !this.#fontsReady;
     }
-
     /**
      * Public initializer (optional, as constructor starts it)
      * Kept for compatibility if manual re-init is needed

src/widgets/ComparisonSlider/ui/ComparisonSlider/ComparisonSlider.svelte

@@ -167,10 +167,6 @@ $effect(() => {
                     {char}
                     {proximity}
                     {isPast}
-                    weight={typography.weight}
-                    size={typography.renderedSize}
-                    fontAName={fontA.name}
-                    fontBName={fontB.name}
                 />
             {/if}
         {/each}
@@ -202,7 +198,9 @@ $effect(() => {
     >
         <!-- Text Rendering Container -->
         {#if isLoading}
+            <div out:fade={{ duration: 300 }}>
                 <Loader size={24} />
+            </div>
         {:else}
             <div
                 class="

src/widgets/ComparisonSlider/ui/ComparisonSlider/components/CharacterSlot.svelte

@@ -3,7 +3,10 @@
     Renders a character with particular styling based on proximity, isPast, weight, fontAName, and fontBName.
 -->
 <script lang="ts">
+import { appliedFontsManager } from '$entities/Font';
+import { getFontUrl } from '$entities/Font/lib';
 import { cn } from '$shared/shadcn/utils/shadcn-utils';
+import { comparisonStore } from '../../../model';
 
 interface Props {
     /**
@@ -18,35 +21,51 @@ interface Props {
      * Flag indicating whether character needed to be changed
      */
     isPast: boolean;
-    /**
-     * Font weight of the character
-     */
-    weight: number;
-    /**
-     * Font size of the character
-     */
-    size: number;
-    /**
-     * Name of the font for the character after the change
-     */
-    fontAName: string;
-    /**
-     * Name of the font for the character before the change
-     */
-    fontBName: string;
 }
 
-let { char, proximity, isPast, weight, size, fontAName, fontBName }: Props = $props();
+let { char, proximity, isPast }: Props = $props();
+
+const fontA = $derived(comparisonStore.fontA);
+const fontB = $derived(comparisonStore.fontB);
+const typography = $derived(comparisonStore.typography);
+
+$effect(() => {
+    if (!fontA || !fontB) {
+        return;
+    }
+
+    const urlA = getFontUrl(fontA, typography.weight);
+    const urlB = getFontUrl(fontB, typography.weight);
+
+    if (!urlA || !urlB) {
+        return;
+    }
+
+    appliedFontsManager.touch([{
+        id: fontA.id,
+        weight: typography.weight,
+        name: fontA.name,
+        url: urlA,
+        isVariable: fontA.features.isVariable,
+    }, {
+        id: fontB.id,
+        weight: typography.weight,
+        name: fontB.name,
+        url: urlB,
+        isVariable: fontB.features.isVariable,
+    }]);
+});
 </script>
 
+{#if fontA && fontB}
     <span
         class={cn(
             'inline-block transition-all duration-300 ease-out will-change-transform',
             isPast ? 'text-indigo-500' : 'text-neutral-950',
         )}
-    style:font-family={isPast ? fontBName : fontAName}
+        style:font-family={isPast ? fontB.name : fontA.name}
-    style:font-weight={weight}
+        style:font-weight={typography.weight}
-    style:font-size={`${size}px`}
+        style:font-size={`${typography.renderedSize}px`}
         style:transform="
         scale({1 + proximity * 0.3})
         translateY({-proximity * 12}px)
@@ -58,6 +77,7 @@ let { char, proximity, isPast, weight, size, fontAName, fontBName }: Props = $pr
     >
         {char === ' ' ? '\u00A0' : char}
     </span>
+{/if}
 
 <style>
 span {

src/widgets/ComparisonSlider/ui/ComparisonSlider/components/Controls.svelte

@@ -1,4 +1,6 @@
 <script lang="ts">
+import { appliedFontsManager } from '$entities/Font';
+import { getFontUrl } from '$entities/Font/lib';
 import type { ResponsiveManager } from '$shared/lib';
 import { cn } from '$shared/shadcn/utils/shadcn-utils';
 import {
@@ -23,8 +25,27 @@ let { sliderPos, isDragging, typographyControls = $bindable<HTMLDivElement | nul
 const fontA = $derived(comparisonStore.fontA);
 const fontB = $derived(comparisonStore.fontB);
 const isLoading = $derived(comparisonStore.isLoading || !comparisonStore.isReady);
+const weight = $derived(comparisonStore.typography.weight);
 
 const responsive = getContext<ResponsiveManager>('responsive');
+
+$effect(() => {
+    if (!fontA || !fontB) {
+        return;
+    }
+
+    const fontAUrl = getFontUrl(fontA, weight);
+    const fontBUrl = getFontUrl(fontB, weight);
+
+    if (!fontAUrl || !fontBUrl) {
+        return;
+    }
+
+    const fontAConfig = { id: fontA.id, name: fontA.name, url: fontAUrl, weight: weight };
+    const fontBConfig = { id: fontB.id, name: fontB.name, url: fontBUrl, weight: weight };
+
+    appliedFontsManager.touch([fontAConfig, fontBConfig]);
+});
 </script>
 
 {#if responsive.isMobile}

src/widgets/ComparisonSlider/ui/ComparisonSlider/components/SelectComparedFonts.svelte

@@ -70,7 +70,7 @@ function selectFontB(font: UnifiedFont) {
                 )}
             >
                 <div class="text-left flex-1 min-w-0">
-                    <FontApplicator name={font.name} id={font.id} {url}>
+                    <FontApplicator {font} weight={typography.weight}>
                         {font.name}
                     </FontApplicator>
                 </div>
@@ -95,9 +95,8 @@ function selectFontB(font: UnifiedFont) {
                                 onclick={handleClick}
                             >
                                 <FontApplicator
-                                    name={fontListItem.name}
+                                    font={fontListItem}
-                                    id={fontListItem.id}
+                                    weight={typography.weight}
-                                    url={getFontUrl(fontListItem, typography.weight) ?? ''}
                                 >
                                     {fontListItem.name}
                                 </FontApplicator>

src/widgets/ComparisonSlider/ui/ComparisonSlider/components/SliderLine.svelte

@@ -4,6 +4,8 @@
 -->
 <script lang="ts">
 import { cn } from '$shared/shadcn/utils/shadcn-utils';
+import { cubicOut } from 'svelte/easing';
+import { fade } from 'svelte/transition';
 
 interface Props {
     /**
@@ -27,6 +29,7 @@ let { sliderPos, isDragging }: Props = $props();
     )}
     style:left="{sliderPos}%"
     style:will-change={isDragging ? 'left' : 'auto'}
+    in:fade={{ duration: 300, delay: 150, easing: cubicOut }}
 >
     <!-- We use part of lucide cursor svg icon as a handle -->
     <svg

src/widgets/ComparisonSlider/ui/ComparisonSlider/components/TypographyControls.svelte

@@ -14,6 +14,7 @@ import {
 import { comparisonStore } from '$widgets/ComparisonSlider/model';
 import AArrowUP from '@lucide/svelte/icons/a-arrow-up';
 import { type Orientation } from 'bits-ui';
+import { untrack } from 'svelte';
 import { Spring } from 'svelte/motion';
 import { fade } from 'svelte/transition';
 
@@ -74,7 +75,10 @@ function handleInputFocus() {
 
 // Movement Logic
 $effect(() => {
-    if (containerWidth === 0 || panelWidth === 0 || staticPosition) return;
+    if (containerWidth === 0 || panelWidth === 0 || staticPosition) {
+        return;
+    }
+
     const sliderX = (sliderPos / 100) * containerWidth;
     const buffer = 40;
     const leftTrigger = margin + panelWidth + buffer;
@@ -88,21 +92,29 @@ $effect(() => {
 });
 
 $effect(() => {
-    const targetX = side === 'right' ? containerWidth - panelWidth - margin * 2 : 0;
+    // Trigger only when side changes
+    const currentSide = side;
+
+    untrack(() => {
         if (containerWidth > 0 && panelWidth > 0) {
+            const targetX = currentSide === 'right'
+                ? containerWidth - panelWidth - margin * 2
+                : 0;
+
             // On side change set the position and the rotation
             xSpring.target = targetX;
-        rotateSpring.target = side === 'right' ? 3.5 : -3.5;
+            rotateSpring.target = currentSide === 'right' ? 3.5 : -3.5;
+
+            if (timeoutId) clearTimeout(timeoutId);
 
             timeoutId = setTimeout(() => {
                 rotateSpring.target = 0;
             }, 600);
         }
+    });
 
     return () => {
-        if (timeoutId) {
+        if (timeoutId) clearTimeout(timeoutId);
-            clearTimeout(timeoutId);
-        }
     };
 });
 </script>