Custom emoji, downvotes, blurhash and focal points on the cards

What other platforms send now shows as they meant it:
- custom emoji (a post's or account's :shortcode:) as their pictures in
  posts, names, content warnings, bios and fields: only the shortcodes the
  server listed, only http(s) pictures, never inside a tag, the shortcode
  kept as alt text;
- a threadiverse post's downvotes next to its favourites;
- blurhash placeholders until a picture loads (wwwroot/js/blurhash.js, a
  small decoder that watches the page), and a picture's focal point;
- an event's online link, participants and capacity, and whether it is
  tentative or cancelled.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw

CLAUDE.md

@@ -224,6 +224,11 @@ supplies:
   with its own `PublicAct`: joining an event (owner decision 2026-10-05) is asked once more, since the event's server
   shows who takes part. An event card shows the persona's participation (`privapub.event.participation`: pending,
   accepted, rejected) with Join or Leave, except for events by invitation or taken on another site (`join_mode`).
+- **What a card shows of other platforms:** custom emoji (`Helpers/CustomEmojis.cs`: a post's or account's `:shortcode:`
+  in its text, name, warning, bio and fields, as the picture the server listed, never inside a tag), a threadiverse
+  post's downvotes next to its favourites, blurhash placeholders until a picture loads (`wwwroot/js/blurhash.js`
+  watches the page for `img[data-blurhash]`), a picture's focal point (`object-position`), and an event's online
+  link, participants and status.
 - **Profiles and search** (`Pages/Profile.razor` at `/account/{id}`, `Pages/Search.razor` at `/search?q=`): a card's
   author and a notification's account open the profile in the app; "Open original" is the only way to the remote site.
   A card in a fixed-height flex column with `overflow-hidden` needs `flex-none`, or it collapses to nothing.

Components/Content.razor

@@ -54,7 +54,7 @@
 			{
 				<p class="inline-flex flex-1 items-center gap-2 min-w-0 text-xs">
 					<i class="ion-md-repeat text-info" aria-hidden="true"></i>
-					<a class="font-bold truncate" href="@booster.Url" target="_blank" rel="noopener noreferrer" title="@booster.Acct">@booster.Name</a>
+					<a class="font-bold truncate" href="@booster.Url" target="_blank" rel="noopener noreferrer" title="@booster.Acct">@CustomEmojis.Text(booster.Name, booster.Emojis)</a>
 					<span>@Localizer["boosted"]</span>
 				</p>
 			}
@@ -81,7 +81,7 @@
 				<header class="flex flex-wrap items-baseline gap-x-2 gap-y-1 min-w-0 justify-between text-xs md:text-sm">
 					<NerdTip Heading="@Localizer["Author"]" Rows="AuthorRows()" Pending="isReadingServer" OnOpen="ReadServer" Align="DTooltipAlign.Start" Class="min-w-0 flex-1">
 						<span class="inline-flex gap-2 min-w-0 max-w-full">
-							<b class="shrink truncate" title="@status.Account?.Name">@status.Account?.Name</b>
+							<b class="shrink truncate" title="@status.Account?.Name">@CustomEmojis.Text(status.Account?.Name, status.Account?.Emojis ?? [])</b>
 							<span class="flex-1 min-w-6 opacity-50 truncate self-center text-xs">@("@" + status.Account?.Acct)</span>
 						</span>
 					</NerdTip>
@@ -137,7 +137,7 @@
 						<DCollapse @bind-IsOpen="isSpoilerOpen" Icon="DCollapseIcon.Arrow" class="rounded-lg neo-xs" HeaderClass="text-sm py-2 min-h-0"
 								   ContentClass="text-sm">
 							<Header>
-								<span class="inline-flex gap-2 items-center"><i class="ion-md-warning text-warning"></i>@spoiler</span>
+								<span class="inline-flex gap-2 items-center"><i class="ion-md-warning text-warning"></i>@CustomEmojis.Text(spoiler, status.Emojis)</span>
 							</Header>
 							<ChildContent>
 								@Body(status)
@@ -229,6 +229,13 @@
 										<span>@status.FavouritesCount</span>
 									}
 								</DButton>
+								@* a threadiverse post's downvotes: its upvotes are its favourites *@
+								@if (status.Privapub?.Votes is { Down: > 0 } votes)
+								{
+									<span class="inline-flex items-center gap-1 px-1 text-sm opacity-70 tabular-nums" title="@Localizer["Downvotes"]" data-downvotes>
+										<i aria-hidden="true" class="ion-md-arrow-down"></i>@votes.Down
+									</span>
+								}
 								<DButton Size="DSize.Sm" Active="status.Bookmarked" Disabled="IsDefaultDisabled || isActing"
 										 OnClick="() => Act(status.Bookmarked ? StatusAction.Unbookmark : StatusAction.Bookmark)" title="@Localizer["Bookmark"]">
 									<i aria-hidden="true" class="ion-md-bookmark text-lg @(status.Bookmarked ? "text-warning" : null)"></i>
@@ -400,7 +407,7 @@
 	RenderFragment Body(Status status) => @<div class="flex flex-col gap-3">
 		@if (status.Content is { Length: > 0 } content)
 		{
-			<div class="post-content text-sm md:text-base break-words">@((MarkupString)content)</div>
+			<div class="post-content text-sm md:text-base break-words">@((MarkupString)CustomEmojis.Html(content, status.Emojis))</div>
 		}
 
 		@if (status.MediaAttachments.Count > 0)
@@ -492,6 +499,25 @@
 				{
 					<span class="inline-flex gap-2 items-center"><i class="ion-md-pin"></i>@(venue.Name ?? venue.Address ?? venue.Url)</span>
 				}
+				@if (IsWebLink(happening.OnlineUrl))
+				{
+					<a class="inline-flex gap-2 items-center link" href="@happening.OnlineUrl" target="_blank" rel="noopener noreferrer"><i class="ion-md-globe"></i>@Localizer["Online"]</a>
+				}
+				@if (happening.Participants is { } going)
+				{
+					<span class="inline-flex gap-2 items-center tabular-nums">
+						<i class="ion-md-people"></i>@(happening.Capacity is { } capacity ? Localizer["{0} of {1} going", going, capacity] : Localizer["{0} going", going])
+					</span>
+				}
+				@switch (happening.Status?.ToUpperInvariant())
+				{
+					case "CANCELLED":
+						<span class="badge badge-error badge-sm">@Localizer["Cancelled"]</span>
+						break;
+					case "TENTATIVE":
+						<span class="badge badge-warning badge-sm">@Localizer["Tentative"]</span>
+						break;
+				}
 				@if (CanJoin(happening))
 				{
 					<div class="flex flex-wrap gap-2 items-center" data-participation="@(happening.Participation ?? "none")">
@@ -544,7 +570,7 @@
 	{
 		"image" => @<a class="block w-full" href="@media.Url" target="_blank" rel="noopener noreferrer">
 			<img alt="@media.Description" title="@media.Description" loading="lazy" class="w-full rounded-lg object-cover @(several ? "aspect-square" : "max-h-[60vh]")"
-				 src="@(media.PreviewUrl ?? media.Url)" />
+				 src="@(media.PreviewUrl ?? media.Url)" data-blurhash="@media.Blurhash" style="@FocalPoint(media)" />
 		</a>,
 		"gifv" => @<video class="w-full rounded-lg" autoplay muted loop playsinline title="@media.Description" src="@media.Url"></video>,
 		"video" => @<video class="w-full max-h-[50vh] aspect-video rounded-lg neo-inset neo-2xs" controls playsinline preload="metadata"
@@ -785,6 +811,13 @@
 
 	static string Number(double? value) => value?.ToString("0.#", System.Globalization.CultureInfo.CurrentCulture) ?? "?";
 
+	// where a cropped picture keeps its subject: Mastodon's focus runs from -1 to 1, left to right and bottom to top
+	static string FocalPoint(MediaAttachment media) => media.Meta?.Focus is { } focus
+		? string.Create(System.Globalization.CultureInfo.InvariantCulture, $"object-position: {(focus.X + 1) * 50:0.#}% {(1 - focus.Y) * 50:0.#}%")
+		: null;
+
+	static bool IsWebLink(string url) => Uri.TryCreate(url, UriKind.Absolute, out var uri) && uri.Scheme is "https" or "http";
+
 	static string CardHost(string url) => Uri.TryCreate(url, UriKind.Absolute, out var uri) ? uri.Host : url;
 
 	// PrivaPub (like Mastodon) answers a placeholder for a missing header: /media/missing-header.png.

Helpers/CustomEmojis.cs

@@ -0,0 +1,47 @@
+using System.Net;
+using System.Text.RegularExpressions;
+
+using decePubClient.Models.Mastodon;
+
+using Microsoft.AspNetCore.Components;
+
+namespace decePubClient.Helpers
+{
+	/// <summary>
+	/// A post's or an account's custom emoji (`:shortcode:` among its <c>emojis</c>) shown as their pictures. The shortcode
+	/// stays as the picture's alt text, so it is what a screen reader reads and what is copied. Only shortcodes the
+	/// server listed for that post or account are replaced, and only with an http(s) picture.
+	/// </summary>
+	public static partial class CustomEmojis
+	{
+		[GeneratedRegex(@":([A-Za-z0-9_+-]{1,64}):")]
+		private static partial Regex Shortcode();
+
+		[GeneratedRegex(@"(<[^>]*>)")]
+		private static partial Regex Tag();
+
+		/// <summary>Plain text (a name, a content warning): escaped, then its shortcodes as pictures.</summary>
+		public static MarkupString Text(string text, IReadOnlyCollection<CustomEmoji> emojis) =>
+			new(Replace(WebUtility.HtmlEncode(text ?? string.Empty), emojis));
+
+		/// <summary>HTML the server sanitized: the shortcodes in its text, never inside a tag.</summary>
+		public static string Html(string html, IReadOnlyCollection<CustomEmoji> emojis) =>
+			emojis.Count == 0 || string.IsNullOrEmpty(html)
+				? html
+				: string.Concat(Tag().Split(html).Select(part => part.StartsWith('<') ? part : Replace(part, emojis)));
+
+		static string Replace(string text, IReadOnlyCollection<CustomEmoji> emojis)
+		{
+			if (emojis.Count == 0 || !text.Contains(':'))
+				return text;
+			var known = new Dictionary<string, string>(StringComparer.Ordinal);
+			foreach (var emoji in emojis)
+				if (!string.IsNullOrEmpty(emoji.Shortcode) && Uri.TryCreate(emoji.Url, UriKind.Absolute, out var url)
+					&& url.Scheme is "https" or "http")
+					known.TryAdd(emoji.Shortcode, url.AbsoluteUri);
+			return Shortcode().Replace(text, match => known.TryGetValue(match.Groups[1].Value, out var url)
+				? $"<img class=\"custom-emoji\" src=\"{WebUtility.HtmlEncode(url)}\" alt=\"{match.Value}\" title=\"{match.Value}\" draggable=\"false\" />"
+				: match.Value);
+		}
+	}
+}

Pages/Profile.razor

@@ -39,7 +39,7 @@
 					<img alt="" class="h-20 w-20 md:h-24 md:w-24 flex-none object-cover rounded-full neo-raised neo-2xs bg-base-100"
 						 src="@(account.Avatar ?? "imgs/icon-192.png")" />
 					<div class="flex flex-col min-w-0 flex-1 pb-1">
-						<b class="text-lg truncate">@account.Name</b>
+						<b class="text-lg truncate">@CustomEmojis.Text(account.Name, account.Emojis)</b>
 						<span class="text-sm opacity-70 truncate">@("@" + FullAcct)</span>
 					</div>
 					@if (!IsOwn)
@@ -111,7 +111,7 @@
 
 				@if (!string.IsNullOrWhiteSpace(account.Note))
 				{
-					<div class="post-content px-4 pt-3 text-sm md:text-base break-words">@((MarkupString)account.Note)</div>
+					<div class="post-content px-4 pt-3 text-sm md:text-base break-words">@((MarkupString)CustomEmojis.Html(account.Note, account.Emojis))</div>
 				}
 
 				@if (account.Fields.Count > 0)
@@ -119,8 +119,8 @@
 					<dl class="grid grid-cols-[minmax(0,10rem)_minmax(0,1fr)] gap-x-3 gap-y-1 px-4 pt-3 text-sm">
 						@foreach (var field in account.Fields)
 						{
-							<dt class="font-semibold truncate">@field.Name</dt>
-							<dd class="post-content break-words min-w-0">@((MarkupString)field.Value)</dd>
+							<dt class="font-semibold truncate">@CustomEmojis.Text(field.Name, account.Emojis)</dt>
+							<dd class="post-content break-words min-w-0">@((MarkupString)CustomEmojis.Html(field.Value, account.Emojis))</dd>
 						}
 					</dl>
 				}

Resources/AllStrings.it.resx

@@ -1577,4 +1577,22 @@
   <data name="The event&#x27;s server shows who takes part, {0} included. Your other personas are never named." xml:space="preserve">
     <value>Il server dell'evento mostra chi partecipa, {0} compreso. Le tue altre persone non vengono mai nominate.</value>
   </data>
+  <data name="Downvotes" xml:space="preserve">
+    <value>Voti negativi</value>
+  </data>
+  <data name="Online" xml:space="preserve">
+    <value>Online</value>
+  </data>
+  <data name="{0} going" xml:space="preserve">
+    <value>{0} partecipano</value>
+  </data>
+  <data name="{0} of {1} going" xml:space="preserve">
+    <value>{0} su {1} partecipano</value>
+  </data>
+  <data name="Cancelled" xml:space="preserve">
+    <value>Annullato</value>
+  </data>
+  <data name="Tentative" xml:space="preserve">
+    <value>Da confermare</value>
+  </data>
 </root>

Resources/AllStrings.resx

@@ -1577,4 +1577,22 @@
   <data name="The event&#x27;s server shows who takes part, {0} included. Your other personas are never named." xml:space="preserve">
     <value>The event's server shows who takes part, {0} included. Your other personas are never named.</value>
   </data>
+  <data name="Downvotes" xml:space="preserve">
+    <value>Downvotes</value>
+  </data>
+  <data name="Online" xml:space="preserve">
+    <value>Online</value>
+  </data>
+  <data name="{0} going" xml:space="preserve">
+    <value>{0} going</value>
+  </data>
+  <data name="{0} of {1} going" xml:space="preserve">
+    <value>{0} of {1} going</value>
+  </data>
+  <data name="Cancelled" xml:space="preserve">
+    <value>Cancelled</value>
+  </data>
+  <data name="Tentative" xml:space="preserve">
+    <value>Tentative</value>
+  </data>
 </root>

Styles/feed.css

@@ -25,6 +25,16 @@
 		display: none;
 	}
 
+	/* a custom emoji (CustomEmojis): the height of the text it sits in */
+	.custom-emoji {
+		display: inline;
+		height: 1.3em;
+		width: auto;
+		max-width: 3em;
+		vertical-align: -0.25em;
+		object-fit: contain;
+	}
+
 	.post-content .ellipsis::after {
 		content: "…";
 	}

wwwroot/index.html

@@ -28,6 +28,7 @@
 	<script>navigator.serviceWorker.register('service-worker.js');</script>
 	<script type="module" src="vendor/cally.js"></script>
 	<script src="main.js"></script>
+	<script src="js/blurhash.js"></script>
 </body>
 
 </html>

wwwroot/js/blurhash.js

@@ -0,0 +1,95 @@
+// Blurhash placeholders (https://blurha.sh): an image carrying data-blurhash shows the colours its hash encodes,
+// decoded into a small canvas, until it has loaded. The page is watched, so the cards rendered later get theirs too.
+(() => {
+	const alphabet = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz#$%*+,-.:;=?@[]^_{|}~"
+	const size = 32
+
+	const base83 = (text) => {
+		let value = 0
+		for (const c of text) {
+			const digit = alphabet.indexOf(c)
+			if (digit < 0)
+				throw new Error("not a blurhash")
+			value = value * 83 + digit
+		}
+		return value
+	}
+	const toLinear = (value) => {
+		const v = value / 255
+		return v <= 0.04045 ? v / 12.92 : Math.pow((v + 0.055) / 1.055, 2.4)
+	}
+	const toSrgb = (value) => {
+		const v = Math.max(0, Math.min(1, value))
+		return Math.round(v <= 0.0031308 ? v * 12.92 * 255 : (1.055 * Math.pow(v, 1 / 2.4) - 0.055) * 255)
+	}
+	const signedSquare = (value) => Math.sign(value) * value * value
+
+	// the hash's pixels at size × size, or null when it is not a blurhash
+	function decode(hash) {
+		if (!hash || hash.length < 6)
+			return null
+		const dimensions = base83(hash[0])
+		const columns = (dimensions % 9) + 1, rows = Math.floor(dimensions / 9) + 1
+		if (hash.length !== 4 + 2 * columns * rows)
+			return null
+		const maximum = (base83(hash[1]) + 1) / 166
+		const average = base83(hash.slice(2, 6))
+		const colours = [[toLinear(average >> 16), toLinear((average >> 8) & 255), toLinear(average & 255)]]
+		for (let i = 1; i < columns * rows; i++) {
+			const value = base83(hash.slice(4 + i * 2, 6 + i * 2))
+			const channel = (quantised) => signedSquare((quantised - 9) / 9) * maximum
+			colours.push([channel(Math.floor(value / 361)), channel(Math.floor(value / 19) % 19), channel(value % 19)])
+		}
+		const pixels = new Uint8ClampedArray(size * size * 4)
+		for (let y = 0; y < size; y++)
+			for (let x = 0; x < size; x++) {
+				let r = 0, g = 0, b = 0
+				for (let j = 0; j < rows; j++)
+					for (let i = 0; i < columns; i++) {
+						const basis = Math.cos(Math.PI * x * i / size) * Math.cos(Math.PI * y * j / size)
+						const colour = colours[i + j * columns]
+						r += colour[0] * basis
+						g += colour[1] * basis
+						b += colour[2] * basis
+					}
+				const p = 4 * (x + y * size)
+				pixels[p] = toSrgb(r)
+				pixels[p + 1] = toSrgb(g)
+				pixels[p + 2] = toSrgb(b)
+				pixels[p + 3] = 255
+			}
+		return pixels
+	}
+
+	function paint(image) {
+		if (image.dataset.blurhashPainted || (image.complete && image.naturalWidth))
+			return
+		image.dataset.blurhashPainted = "1"
+		try {
+			const pixels = decode(image.dataset.blurhash)
+			if (!pixels)
+				return
+			const canvas = document.createElement("canvas")
+			canvas.width = size
+			canvas.height = size
+			canvas.getContext("2d").putImageData(new ImageData(pixels, size, size), 0, 0)
+			image.style.backgroundImage = `url(${canvas.toDataURL()})`
+			image.style.backgroundSize = "cover"
+			image.addEventListener("load", () => image.style.removeProperty("background-image"), { once: true })
+		} catch (e) {
+			window.logFromJs?.(e.message, "blurhash")
+		}
+	}
+
+	const scan = (root) => root.querySelectorAll("img[data-blurhash]").forEach(paint)
+	new MutationObserver(records => {
+		for (const record of records)
+			for (const node of record.addedNodes)
+				if (node.nodeType === Node.ELEMENT_NODE) {
+					if (node.matches("img[data-blurhash]"))
+						paint(node)
+					scan(node)
+				}
+	}).observe(document.documentElement, { childList: true, subtree: true })
+	scan(document)
+})()