From b304e841de5ee97834006b334818e1cb68dd7d10 Mon Sep 17 00:00:00 2001
From: Ilia Mashkov <hikkikomori7@gmail.com>
Date: Fri, 6 Feb 2026 12:04:32 +0300
Subject: [PATCH] feat(ComparisonSlider): integrate loader and add animations
 for appearance/disappearance

---
 .../ComparisonSlider/ComparisonSlider.svelte  | 64 +++++++++++--------
 .../components/ControlsWrapper.svelte         |  3 +
 .../ComparisonSlider/components/Labels.svelte |  3 +
 3 files changed, 43 insertions(+), 27 deletions(-)

diff --git a/src/widgets/ComparisonSlider/ui/ComparisonSlider/ComparisonSlider.svelte b/src/widgets/ComparisonSlider/ui/ComparisonSlider/ComparisonSlider.svelte
index 2120233..bcd3eef 100644
--- a/src/widgets/ComparisonSlider/ui/ComparisonSlider/ComparisonSlider.svelte
+++ b/src/widgets/ComparisonSlider/ui/ComparisonSlider/ComparisonSlider.svelte
@@ -15,8 +15,10 @@ import {
     createTypographyControl,
 } from '$shared/lib';
 import type { LineData } from '$shared/lib';
+import { Loader } from '$shared/ui';
 import { comparisonStore } from '$widgets/ComparisonSlider/model';
 import { Spring } from 'svelte/motion';
+import { fade } from 'svelte/transition';
 import CharacterSlot from './components/CharacterSlot.svelte';
 import ControlsWrapper from './components/ControlsWrapper.svelte';
 import Labels from './components/Labels.svelte';
@@ -26,6 +28,8 @@ import SliderLine from './components/SliderLine.svelte';
 const fontA = $derived(comparisonStore.fontA);
 const fontB = $derived(comparisonStore.fontB);
 
+const isLoading = $derived(comparisonStore.isLoading || !comparisonStore.isReady);
+
 let container: HTMLElement | undefined = $state();
 let controlsWrapperElement = $state<HTMLDivElement | null>(null);
 let measureCanvas: HTMLCanvasElement | undefined = $state();
@@ -164,31 +168,33 @@ $effect(() => {
     </div>
 {/snippet}
 
-{#if fontA && fontB}
-    <!-- Hidden canvas used for text measurement by the helper -->
-    <canvas bind:this={measureCanvas} class="hidden" width="1" height="1"></canvas>
+<!-- Hidden canvas used for text measurement by the helper -->
+<canvas bind:this={measureCanvas} class="hidden" width="1" height="1"></canvas>
 
-    <div class="relative">
-        <div
-            bind:this={container}
-            role="slider"
-            tabindex="0"
-            aria-valuenow={Math.round(sliderPos)}
-            aria-label="Font comparison slider"
-            onpointerdown={startDragging}
-            class="
-                group relative w-full py-16 px-24 sm:py-24 sm:px-24 overflow-hidden
-                rounded-[2.5rem]
-                select-none touch-none cursor-ew-resize min-h-100 flex flex-col justify-center
-                backdrop-blur-lg bg-gradient-to-br from-gray-100/70 via-white/50 to-gray-100/60
-                border border-gray-300/40
-                shadow-[inset_0_4px_12px_0_rgba(0,0,0,0.12),inset_0_2px_4px_0_rgba(0,0,0,0.08),0_1px_2px_0_rgba(255,255,255,0.8)]
-                before:absolute before:inset-0 before:rounded-[2.5rem] before:p-[1px]
-                before:bg-gradient-to-br before:from-black/5 before:via-black/2 before:to-transparent
-                before:-z-10 before:blur-sm
-            "
-        >
-            <!-- Text Rendering Container -->
+<div class="relative">
+    <div
+        bind:this={container}
+        role="slider"
+        tabindex="0"
+        aria-valuenow={Math.round(sliderPos)}
+        aria-label="Font comparison slider"
+        onpointerdown={startDragging}
+        class="
+            group relative w-full py-16 px-24 sm:py-24 sm:px-24 overflow-hidden
+            rounded-[2.5rem]
+            select-none touch-none cursor-ew-resize min-h-100 flex flex-col justify-center
+            backdrop-blur-lg bg-gradient-to-br from-gray-100/70 via-white/50 to-gray-100/60
+            border border-gray-300/40
+            shadow-[inset_0_4px_12px_0_rgba(0,0,0,0.12),inset_0_2px_4px_0_rgba(0,0,0,0.08),0_1px_2px_0_rgba(255,255,255,0.8)]
+            before:absolute before:inset-0 before:rounded-[2.5rem] before:p-[1px]
+            before:bg-gradient-to-br before:from-black/5 before:via-black/2 before:to-transparent
+            before:-z-10 before:blur-sm
+        "
+    >
+        <!-- Text Rendering Container -->
+        {#if isLoading}
+            <Loader size={24} />
+        {:else}
             <div
                 class="
                     relative flex flex-col items-center gap-4
@@ -197,6 +203,8 @@ $effect(() => {
                     drop-shadow-[0_3px_6px_rgba(255,255,255,0.9)]
                 "
                 style:perspective="1000px"
+                in:fade={{ duration: 300, delay: 300 }}
+                out:fade={{ duration: 300 }}
             >
                 {#each charComparison.lines as line, lineIndex}
                     <div
@@ -212,8 +220,10 @@ $effect(() => {
             </div>
 
             <SliderLine {sliderPos} {isDragging} />
-        </div>
+        {/if}
+    </div>
 
+    {#if fontA && fontB && !isLoading}
         <Labels {fontA} {fontB} {sliderPos} weight={weightControl.value} />
         <!-- Since there're slider controls inside we put them outside the main one -->
         <ControlsWrapper
@@ -226,5 +236,5 @@ $effect(() => {
             {sizeControl}
             {heightControl}
         />
-    </div>
-{/if}
+    {/if}
+</div>
diff --git a/src/widgets/ComparisonSlider/ui/ComparisonSlider/components/ControlsWrapper.svelte b/src/widgets/ComparisonSlider/ui/ComparisonSlider/components/ControlsWrapper.svelte
index c23106b..7dd0fe7 100644
--- a/src/widgets/ComparisonSlider/ui/ComparisonSlider/components/ControlsWrapper.svelte
+++ b/src/widgets/ComparisonSlider/ui/ComparisonSlider/components/ControlsWrapper.svelte
@@ -12,6 +12,7 @@ import { ComboControlV2 } from '$shared/ui';
 import { ExpandableWrapper } from '$shared/ui';
 import AArrowUP from '@lucide/svelte/icons/a-arrow-up';
 import { Spring } from 'svelte/motion';
+import { fade } from 'svelte/transition';
 
 interface Props {
     /**
@@ -121,6 +122,8 @@ $effect(() => {
         translateX({xSpring.current}px)
         rotateZ({rotateSpring.current}deg)
     "
+    in:fade={{ duration: 300, delay: 300 }}
+    out:fade={{ duration: 300, delay: 300 }}
 >
     <ExpandableWrapper
         bind:element={wrapper}
diff --git a/src/widgets/ComparisonSlider/ui/ComparisonSlider/components/Labels.svelte b/src/widgets/ComparisonSlider/ui/ComparisonSlider/components/Labels.svelte
index 2475288..71f0f53 100644
--- a/src/widgets/ComparisonSlider/ui/ComparisonSlider/components/Labels.svelte
+++ b/src/widgets/ComparisonSlider/ui/ComparisonSlider/components/Labels.svelte
@@ -17,6 +17,7 @@ import {
 } from '$shared/shadcn/ui/select';
 import { cn } from '$shared/shadcn/utils/shadcn-utils';
 import { comparisonStore } from '$widgets/ComparisonSlider/model';
+import { fade } from 'svelte/transition';
 
 interface Props<T> {
     /**
@@ -60,6 +61,8 @@ function selectFontB(font: UnifiedFont) {
     <div
         class="z-50 pointer-events-auto"
         onpointerdown={(e => e.stopPropagation())}
+        in:fade={{ duration: 300, delay: 300 }}
+        out:fade={{ duration: 300, delay: 300 }}
     >
         <SelectRoot type="single" disabled={!fontList.length}>
             <SelectTrigger