Add button and drag to swap colors

src/lib/components/colors/Header.svelte

@@ -4,6 +4,7 @@
 
   import CopyButton from '$lib/components/util/CopyButton.svelte';
   import type { ColorFormatId } from '$lib/constants';
+  import { switchColors } from '$lib/stores';
   import { getSpaceFromFormatId } from '$lib/utils';
 
   interface Props {
@@ -12,6 +13,8 @@
     format: ColorFormatId;
   }
 
+  const CUSTOM_MIMETYPE = 'text/odd';
+
   let { type, color, format }: Props = $props();
 
   let targetSpace = $derived(getSpaceFromFormatId(format));
@@ -20,6 +23,7 @@
   let editing = $state(false);
   let inputValue = $state('');
   let hasError = $state(false);
+  let isDragging = false;
 
   // When not editing, sync input value with color (e.g. when sliders change)
   $effect(() => {
@@ -80,6 +84,32 @@
         break;
     }
   };
+
+  const onDragStart = (event: DragEvent) => {
+    isDragging = true;
+    if (!event.dataTransfer) return;
+    event.dataTransfer.clearData();
+    event.dataTransfer.setData(CUSTOM_MIMETYPE, type);
+  };
+
+  const onDrop = (event: DragEvent | undefined) => {
+    const droppedType = event?.dataTransfer?.getData(CUSTOM_MIMETYPE);
+    const dragIsFromOther =
+      type === 'fg' ? droppedType === 'bg' : droppedType === 'fg';
+    if (dragIsFromOther) {
+      switchColors();
+    }
+  };
+
+  const makeDropable = (event: DragEvent) => {
+    // DataTransfer values are not available on dragover, but because the types
+    // of items is available, we can use a custom mimetype to check if a swatch
+    // is the drag target.
+    if (!isDragging && event?.dataTransfer?.types.includes(CUSTOM_MIMETYPE)) {
+      // Cancelling the event signals that the dragged item can be dropped here.
+      event.preventDefault();
+    }
+  };
 </script>
 
 <div
@@ -88,7 +118,16 @@
   data-column="tool"
   data-needs-changes={hasError}
 >
-  <div class="swatch {type}"></div>
+  <div
+    role="complementary"
+    class="swatch {type}"
+    draggable="true"
+    ondrop={onDrop}
+    ondragenter={makeDropable}
+    ondragover={makeDropable}
+    ondragstart={onDragStart}
+    ondragend={() => (isDragging = false)}
+  ></div>
   <label for="{type}-color" data-label>
     {displayType} Color
   </label>

src/lib/components/colors/SwitchButton.svelte

@@ -0,0 +1,9 @@
+<script lang="ts">
+  import Icon from '$lib/components/util/Icon.svelte';
+  import { switchColors } from '$lib/stores';
+</script>
+
+<button type="button" onclick={switchColors} data-btn="icon switch">
+  <Icon name="switch" />
+  <span class="sr-only">Swap colors</span></button
+>

src/lib/components/colors/index.svelte

@@ -4,6 +4,8 @@
   import Sliders from '$lib/components/colors/Sliders.svelte';
   import SupportWarning from '$lib/components/colors/SupportWarning.svelte';
   import { bg, fg, format } from '$lib/stores';
+
+  import SwitchButton from './SwitchButton.svelte';
 </script>
 
 <h2 class="sr-only">Check the contrast ratio between two colors</h2>
@@ -13,12 +15,14 @@
 <form data-form="contrast-checker" data-layout="color-form">
   <Header type="bg" color={bg} format={$format} />
   <Sliders type="bg" color={bg} format={$format} />
-
+  <div data-actions="swap-colors">
+    <SwitchButton />
+  </div>
   <Header type="fg" color={fg} format={$format} />
   <Sliders type="fg" color={fg} format={$format} />
 </form>
 
-<div data-layout="split">
+<div data-layout="color-formats">
   <Formats type="bg" color={$bg} format={$format} />
   <Formats type="fg" color={$fg} format={$format} />
 </div>
@@ -31,6 +35,11 @@
   }
 
   [data-layout] {
-    column-gap: var(--triple-gutter);
+    column-gap: var(--gutter);
+  }
+
+  [data-actions='swap-colors'] {
+    display: grid;
+    place-content: center;
   }
 </style>

src/lib/components/util/Icon.svelte

@@ -12,6 +12,7 @@
   import OddBird from '$lib/icons/OddBird.svelte';
   import Twitter from '$lib/icons/Twitter.svelte';
   import Warning from '$lib/icons/Warning.svelte';
+  import Switch from '$src/lib/icons/Switch.svelte';
 
   const icons: Record<string, Component> = {
     check: Check,
@@ -25,6 +26,7 @@
     oddbird: OddBird,
     linkedin: LinkedIn,
     mastodon: Mastodon,
+    switch: Switch,
   };
 
   interface Props {

src/lib/icons/Switch.svelte

@@ -0,0 +1,17 @@
+<script lang="ts">
+  let props = $props();
+</script>
+
+<svg
+  xmlns="http://www.w3.org/2000/svg"
+  viewBox="0 0 512 512"
+  width="26"
+  height="26"
+  {...props}
+>
+  <path
+    id="switch"
+    data-name="switch"
+    d="M406.6 374.6l96-96c12.5-12.5 12.5-32.8 0-45.3l-96-96c-12.5-12.5-32.8-12.5-45.3 0s-12.5 32.8 0 45.3L402.7 224l-293.5 0 41.4-41.4c12.5-12.5 12.5-32.8 0-45.3s-32.8-12.5-45.3 0l-96 96c-12.5 12.5-12.5 32.8 0 45.3l96 96c12.5 12.5 32.8 12.5 45.3 0s12.5-32.8 0-45.3L109.3 288l293.5 0-41.4 41.4c-12.5 12.5-12.5 32.8 0 45.3s32.8 12.5 45.3 0z"
+  />
+</svg>

src/lib/stores.ts

@@ -10,7 +10,7 @@ import {
   REC_2020,
   sRGB,
 } from 'colorjs.io/fn';
-import { writable } from 'svelte/store';
+import { get, writable } from 'svelte/store';
 
 // eslint-disable-next-line import/no-unresolved
 import { browser, dev } from '$app/environment';
@@ -57,6 +57,12 @@ export const reset = () => {
   fg.set(INITIAL_FG);
 };
 
+export const switchColors = () => {
+  const temp = get(bg);
+  bg.set(get(fg));
+  fg.set(temp);
+};
+
 /* c8 ignore next 5 */
 if (browser && dev) {
   bg.subscribe(($bg) => (window.bg = $bg));

src/sass/config/scale/_ui.scss

@@ -15,3 +15,6 @@ $icon-medium: 1.5em;
 $ratio-width: 10rem;
 $range-thumb-size: 1.35rem;
 $range-input: 0.85rem;
+$triangle-width: var(--shim);
+$triangle-height: var(--shim-plus);
+$switch-space: var(--double-gutter);

src/sass/initial/_layout.scss

@@ -69,20 +69,28 @@ body {
   grid-template-columns: auto 1fr;
 }
 
-[data-layout~='split'] {
+[data-layout~='color-formats'] {
   display: grid;
 
   @include config.above('sm-page-break') {
-    grid-template-columns: 1fr 1fr;
+    grid-template-columns: 1fr var(--switch-space) 1fr;
+  }
+}
+
+[data-content='formats'] {
+  @include config.above('sm-page-break') {
+    &:last-of-type {
+      grid-column: 3;
+    }
   }
 }
 
 [data-layout='color-form'] {
   @include config.above('sm-page-break') {
     display: grid;
     grid-template:
-      'bginput fginput' auto
-      'bgslide fgslide' auto / 1fr 1fr;
+      'bginput switch fginput' auto
+      'bgslide . fgslide' auto / 1fr var(--switch-space) 1fr;
   }
 }
 

src/sass/patterns/_buttons.scss

@@ -1,6 +1,8 @@
 /// # Button Pattern
 /// @group buttons
 
+@use '../config';
+
 button {
   font-family: inherit;
   font-size: inherit;
@@ -25,7 +27,8 @@ button {
     var(--btn-padding-inline, var(--gutter));
   transition:
     color var(--fast),
-    background-color var(--fast) transform var(--fast);
+    background-color var(--fast),
+    transform var(--fast);
 
   &:hover,
   &:focus {
@@ -47,3 +50,27 @@ button {
     transform: scale(1.15);
   }
 }
+
+[data-btn~='switch'] {
+  --icon-size: var(--icon-medium);
+
+  block-size: fit-content;
+  margin-block-end: var(--spacer);
+
+  @include config.below('sm-page-break') {
+    [data-icon] {
+      transform: rotate(90deg);
+    }
+  }
+
+  &:hover,
+  &:focus {
+    --outline-width: thin;
+
+    transform: var(--transform, rotate(180deg));
+
+    @media (prefers-reduced-motion: reduce) {
+      --transform: scale(1.1);
+    }
+  }
+}