Image Compare

- The frame writes `--pos: <value>%`. The before layer uses
  `clip-path: inset(0 calc(100 - v)% 0 0)` (vertical: `inset(0 0 (100 - v)%
0)`), so both layers keep identical layout and nothing reflows while
  dragging. The divider is a 2px `bg-card` bar at `left: var(--pos)` with a
  hairline ring and `--elevation-sm`; it turns ember while dragging or
  focused (`group-has-focus-visible`).
- Pointer: `pointerdown` captures the pointer on the frame and maps
  `clientX` (or `clientY`) through the frame's rect to percent;
  `touch-none` keeps touch drags from scrolling the page. Hover mode
  updates on every non-touch `pointermove` and makes the knob
  `pointer-events-none` so it never blocks tracking.
- Knob: 36px circle with the lit-key recipe (`from-key-top to-key-bottom`,
  `ring-key-edge`, `--key-shine`), a two-chevron grip icon rotated 90° when
  vertical. Scale transitions at `--motion-fast` with `ease-enter`.
- Chips: `bg-card/85` + `backdrop-blur-sm` raised pills; opacity 0 when the
  value is within 18% (22% vertical) of their edge.

<!-- PEBBLE-LICENSE -->

registry/media/image-compare/image-compare.tsx

"use client";

/* PEBBLE-LICENSE
Built by Pebble. Component: image-compare.

First-party license: MIT

The following first-party terms apply only to original Pebble material.

MIT License

Copyright (c) 2026 Praxys Solutions LLC (Pebble)

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
END PEBBLE-LICENSE */

import * as React from "react";

import { cn } from "@/lib/utils";

export type ImageCompareProps = Omit<React.ComponentProps<"div">, "onChange" | "defaultValue"> & {
  /** Layer shown on the start side (left, or top when vertical). */
  before: React.ReactNode;
  /** Layer shown on the end side (right, or bottom when vertical). */
  after: React.ReactNode;
  /** Chip text over the before side. Empty hides it. */
  beforeLabel?: string;
  /** Chip text over the after side. Empty hides it. */
  afterLabel?: string;
  /** Handle position in percent when uncontrolled. */
  defaultValue?: number;
  /** Handle position in percent (controlled). */
  value?: number;
  /** Called with the new position in percent. */
  onValueChange?: (value: number) => void;
  /** Divider direction: a vertical line moving left/right, or a horizontal line moving up/down. */
  orientation?: "horizontal" | "vertical";
  /** `drag` follows a press; `hover` follows the pointer without pressing. */
  mode?: "drag" | "hover";
  /** Where the chips sit along the divider (horizontal only). */
  labelPosition?: "top" | "bottom";
  /** Accessible name of the slider. */
  label?: string;
};

const clamp = (n: number) => Math.min(100, Math.max(0, n));

export function ImageCompare({
  before,
  after,
  beforeLabel = "Before",
  afterLabel = "After",
  defaultValue = 50,
  value: valueProp,
  onValueChange,
  orientation = "horizontal",
  mode = "drag",
  labelPosition = "top",
  label = "Comparison position",
  className,
  style,
  ...props
}: ImageCompareProps) {
  const [inner, setInner] = React.useState(clamp(defaultValue));
  const value = clamp(valueProp ?? inner);
  const [dragging, setDragging] = React.useState(false);
  const rootRef = React.useRef<HTMLDivElement>(null);
  const handleRef = React.useRef<HTMLDivElement>(null);
  const horizontal = orientation === "horizontal";

  const commit = (next: number) => {
    const v = Math.round(clamp(next) * 10) / 10;
    if (v === value) return;
    if (valueProp === undefined) setInner(v);
    onValueChange?.(v);
  };

  const fromPointer = (event: React.PointerEvent) => {
    const rect = rootRef.current?.getBoundingClientRect();
    if (!rect || !rect.width || !rect.height) return;
    commit(
      horizontal
        ? ((event.clientX - rect.left) / rect.width) * 100
        : ((event.clientY - rect.top) / rect.height) * 100,
    );
  };

  // The before layer is clipped to the start side of the line.
  const clip = horizontal ? `inset(0 ${100 - value}% 0 0)` : `inset(0 0 ${100 - value}% 0)`;
  const valueText = `${Math.round(value)}% ${beforeLabel || "before"}, ${Math.round(100 - value)}% ${afterLabel || "after"}`;

  return (
    <div
      ref={rootRef}
      data-slot="image-compare"
      data-orientation={orientation}
      data-mode={mode}
      data-dragging={dragging || undefined}
      className={cn(
        "group/compare relative isolate touch-none overflow-hidden rounded-xl bg-muted select-none",
        "shadow-raised-md ring-1 inset-shadow-highlight ring-hairline",
        mode === "drag" && (horizontal ? "cursor-ew-resize" : "cursor-ns-resize"),
        className,
      )}
      style={{ "--pos": `${value}%`, ...style } as React.CSSProperties}
      onPointerDown={(event) => {
        if (mode !== "drag" || event.button !== 0) return;
        event.preventDefault();
        event.currentTarget.setPointerCapture(event.pointerId);
        setDragging(true);
        fromPointer(event);
        handleRef.current?.focus({ preventScroll: true });
      }}
      onPointerMove={(event) => {
        if (mode === "hover" ? event.pointerType !== "touch" || event.buttons > 0 : dragging)
          fromPointer(event);
      }}
      onPointerUp={(event) => {
        if (event.currentTarget.hasPointerCapture(event.pointerId))
          event.currentTarget.releasePointerCapture(event.pointerId);
        setDragging(false);
      }}
      onPointerCancel={() => setDragging(false)}
      {...props}
    >
      <div data-slot="image-compare-after" className="absolute inset-0 *:size-full">
        {after}
      </div>
      <div
        data-slot="image-compare-before"
        className="absolute inset-0 *:size-full"
        style={{ clipPath: clip }}
      >
        {before}
      </div>

      {beforeLabel && (
        <Chip
          className={cn("left-3", horizontal && labelPosition === "bottom" ? "bottom-3" : "top-3")}
          hidden={value < (horizontal ? 18 : 22)}
        >
          {beforeLabel}
        </Chip>
      )}
      {afterLabel && (
        <Chip
          className={cn(
            horizontal ? "right-3" : "left-3",
            horizontal && labelPosition === "top" ? "top-3" : "bottom-3",
          )}
          hidden={value > (horizontal ? 82 : 78)}
        >
          {afterLabel}
        </Chip>
      )}

      {/* Divider: a hairline of light with a soft shadow either side. */}
      <div
        aria-hidden
        className={cn(
          "pointer-events-none absolute z-10 bg-card shadow-[0_0_0_1px_var(--hairline),var(--elevation-sm)]",
          "transition-[background-color,box-shadow] duration-(--motion-fast)",
          "group-has-focus-visible/compare:bg-accent group-data-dragging/compare:bg-accent",
          horizontal
            ? "inset-y-0 left-(--pos) w-0.5 -translate-x-1/2"
            : "inset-x-0 top-(--pos) h-0.5 -translate-y-1/2",
        )}
      />

      <div
        ref={handleRef}
        role="slider"
        tabIndex={0}
        aria-label={label}
        aria-orientation={orientation}
        aria-valuemin={0}
        aria-valuemax={100}
        aria-valuenow={Math.round(value)}
        aria-valuetext={valueText}
        data-slot="image-compare-handle"
        onKeyDown={(event) => {
          const big = event.shiftKey ? 10 : 1;
          const map: Record<string, number> = {
            ArrowLeft: value - big,
            ArrowDown: horizontal ? value - big : value + big,
            ArrowRight: value + big,
            ArrowUp: horizontal ? value + big : value - big,
            PageDown: value - 10,
            PageUp: value + 10,
            Home: 0,
            End: 100,
          };
          if (!(event.key in map)) return;
          event.preventDefault();
          commit(map[event.key]);
        }}
        className={cn(
          "absolute z-20 grid size-9 place-items-center rounded-full outline-none",
          horizontal ? "top-1/2 left-(--pos)" : "top-(--pos) left-1/2",
          "-translate-x-1/2 -translate-y-1/2",
          // The lit key: gradient, edge ring, top shine.
          "bg-linear-to-b from-key-top to-key-bottom text-primary-foreground shadow-[var(--key-shine),var(--elevation-md)] ring-1 ring-key-edge",
          "cursor-grab transition-[scale,box-shadow] duration-(--motion-fast) ease-enter group-data-dragging/compare:cursor-grabbing",
          "group-data-dragging/compare:scale-[1.08] group-data-dragging/compare:shadow-[var(--key-shine),var(--elevation-lg)] hover:scale-105",
          "focus-visible:ring-2 focus-visible:ring-ring focus-visible:ring-offset-2 focus-visible:ring-offset-card",
          "motion-reduce:transition-none motion-reduce:group-data-dragging/compare:scale-100 motion-reduce:hover:scale-100",
          mode === "hover" && "pointer-events-none",
        )}
      >
        <svg
          viewBox="0 0 16 16"
          fill="none"
          stroke="currentColor"
          strokeWidth={1.5}
          strokeLinecap="round"
          strokeLinejoin="round"
          aria-hidden
          className={cn("size-4", !horizontal && "rotate-90")}
        >
          <path d="M5.5 4.5 2 8l3.5 3.5M10.5 4.5 14 8l-3.5 3.5" />
        </svg>
      </div>
    </div>
  );
}

function Chip({
  hidden,
  className,
  children,
}: {
  hidden: boolean;
  className?: string;
  children: React.ReactNode;
}) {
  return (
    <span
      aria-hidden
      className={cn(
        "pointer-events-none absolute z-10 rounded-full bg-card/85 px-2.5 py-1 text-xs font-medium text-foreground backdrop-blur-sm",
        "shadow-raised-xs ring-1 inset-shadow-highlight ring-hairline",
        "transition-opacity duration-(--motion-base) ease-enter motion-reduce:transition-none",
        hidden ? "opacity-0" : "opacity-100",
        className,
      )}
    >
      {children}
    </span>
  );
}