Glass card

import { GlassSurface } from "@/components/ui/glass-surface";
import { cn } from "@/lib/utils";

type GlassCardProps = React.ComponentProps<typeof GlassSurface>;

/** A 12px card of glass. Put it over an image or a gradient, since glass only reads over something. */
export function GlassCard({ className, ...props }: GlassCardProps) {
  return (
    <GlassSurface
      data-slot="glass-card"
      radius={12}
      className={cn("flex flex-col gap-1.5 rounded-lg bg-background/60 p-4 text-foreground", className)}
      {...props}
    />
  );
}

export function GlassCardTitle({ className, ...props }: React.ComponentProps<"h3">) {
  return <h3 data-slot="glass-card-title" className={cn("text-sm font-medium", className)} {...props} />;
}

export function GlassCardDescription({ className, ...props }: React.ComponentProps<"p">) {
  return <p data-slot="glass-card-description" className={cn("text-sm text-foreground", className)} {...props} />;
}

"use client";

import * as React from "react";

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

type GlassSurfaceProps = React.ComponentProps<"div"> & {
  /** Corner radius in pixels. Keep it equal to the rounded class on the surface, so the rim follows the edge. */
  radius?: number;
  /** Width of the bent rim in pixels. */
  rim?: number;
  /** How far the rim pushes what is behind it, in pixels. */
  strength?: number;
  /** Frost behind the glass, in pixels. */
  blur?: number;
};

/** Distance from a point to the edge of a rounded rectangle centred on the origin. Negative is inside. */
function roundedBoxDistance(x: number, y: number, halfWidth: number, halfHeight: number, radius: number) {
  const qx = Math.abs(x) - halfWidth + radius;
  const qy = Math.abs(y) - halfHeight + radius;
  return Math.hypot(Math.max(qx, 0), Math.max(qy, 0)) + Math.min(Math.max(qx, qy), 0) - radius;
}

/**
 * Paints a displacement map: red and green hold how far each pixel is pushed, 128 is no push.
 * Inside the rim the push points along the edge normal and falls off with a quarter circle, the
 * profile of a lens edge, so the centre of the glass stays flat.
 */
function paintRefractionMap(width: number, height: number, radius: number, rim: number) {
  const canvas = document.createElement("canvas");
  canvas.width = width;
  canvas.height = height;
  const context = canvas.getContext("2d");
  if (!context) return null;
  const image = context.createImageData(width, height);
  const halfWidth = width / 2;
  const halfHeight = height / 2;
  for (let py = 0; py < height; py++) {
    for (let px = 0; px < width; px++) {
      const x = px + 0.5 - halfWidth;
      const y = py + 0.5 - halfHeight;
      const edge = roundedBoxDistance(x, y, halfWidth, halfHeight, radius);
      const depth = Math.min(Math.max(-edge / rim, 0), 1);
      const bend = 1 - Math.sqrt(1 - (1 - depth) * (1 - depth));
      // The edge normal, by central differences on the distance field.
      const nx = roundedBoxDistance(x + 1, y, halfWidth, halfHeight, radius) - roundedBoxDistance(x - 1, y, halfWidth, halfHeight, radius);
      const ny = roundedBoxDistance(x, y + 1, halfWidth, halfHeight, radius) - roundedBoxDistance(x, y - 1, halfWidth, halfHeight, radius);
      const length = Math.hypot(nx, ny) || 1;
      const at = (py * width + px) * 4;
      image.data[at] = 128 - (nx / length) * bend * 127;
      image.data[at + 1] = 128 - (ny / length) * bend * 127;
      image.data[at + 2] = 128;
      image.data[at + 3] = 255;
    }
  }
  context.putImageData(image, 0, 0);
  return canvas.toDataURL();
}

/**
 * A pane of glass. Chromium bends what is behind it with an SVG filter; every other browser gets the
 * frosted fallback, which is the same surface without the bent rim. Either way the pane keeps enough
 * fill to hold text, and it turns solid for people who ask for less transparency.
 */
function GlassSurface({
  radius = 12,
  rim = 14,
  strength = 40,
  blur = 6,
  className,
  style,
  children,
  ...props
}: GlassSurfaceProps) {
  const id = React.useId().replace(/[^a-zA-Z0-9]/g, "");
  const surface = React.useRef<HTMLDivElement>(null);
  const [map, setMap] = React.useState<string | null>(null);

  React.useEffect(() => {
    const el = surface.current;
    if (!el) return;
    // backdrop-filter with a url() only renders in Chromium, and other browsers can parse it and draw nothing.
    if (!("userAgentData" in navigator) || !CSS.supports("backdrop-filter", "url(#a)")) return;
    const paint = () => {
      const width = Math.round(el.clientWidth);
      const height = Math.round(el.clientHeight);
      if (width > 0 && height > 0) setMap(paintRefractionMap(width, height, radius, rim));
    };
    const observer = new ResizeObserver(paint);
    observer.observe(el);
    return () => observer.disconnect();
  }, [radius, rim]);

  const refracting = map !== null;
  return (
    <div
      ref={surface}
      data-slot="glass-surface"
      data-refracting={refracting || undefined}
      className={cn(
        "relative border bg-background/50 shadow-[inset_0_1px_0_0_color-mix(in_oklab,var(--foreground)_8%,transparent)] backdrop-blur-md contrast-more:bg-background [@media(prefers-reduced-transparency:reduce)]:bg-background [@media(prefers-reduced-transparency:reduce)]:backdrop-blur-none",
        className,
      )}
      style={refracting ? { ...style, backdropFilter: `url(#${id})` } : style}
      {...props}
    >
      {refracting ? (
        <svg aria-hidden="true" width="0" height="0" className="absolute">
          <filter id={id} x="0" y="0" width="100%" height="100%" colorInterpolationFilters="sRGB">
            <feImage href={map ?? undefined} preserveAspectRatio="none" result="map" />
            <feGaussianBlur in="SourceGraphic" stdDeviation={blur} result="frost" />
            <feDisplacementMap in="frost" in2="map" scale={strength} xChannelSelector="R" yChannelSelector="G" />
          </filter>
        </svg>
      ) : null}
      {children}
    </div>
  );
}

export { GlassSurface };