Show how to theme a complete layout

README.md

@@ -22,6 +22,7 @@
   <a href="#quick-start">Quick start</a> ·
   <a href="#packages">Packages</a> ·
   <a href="#unicode-aware-layout">Layout</a> ·
+  <a href="#theme-a-whole-layout">Theming</a> ·
   <a href="#documentation">Documentation</a> ·
   <a href="#contributing">Contributing</a>
 </p>
@@ -62,6 +63,43 @@ and naturally flowing content in HTML.
 
 ![The same MarkupString figure rendered as ANSI terminal art and an HTML image](docs/assets/showcase-image-drawing.png)
 
+## Theme a whole layout
+
+A theme changes semantic parts together: borders, titles, labels, bullets, guides, gauges, table
+headings, and striped rows. Presets can change the drawing characters too; generated palettes build
+accessible colour roles from a single seed.
+
+```csharp
+var registry = MarkupRegistry.Empty.WithAnsi().WithHtml();
+
+var sheet = new Stack(
+[
+    new Fields(
+    [
+        new Field(MarkupText.Plain("Name"), MarkupText.Plain("Lyra Vale")),
+        new Field(MarkupText.Plain("Role"), MarkupText.Plain("Wayfinder")),
+    ]),
+    new Gauge(7, 10) { Label = MarkupText.Plain("Trail") },
+]).Bordered(MarkupText.Plain("WAYFINDER'S JOURNAL"));
+
+var fantasy = sheet.Themed(ThemePalette.Preset("fantasy")!.ToLayoutTheme());
+var housePalette = ThemePalette.Generate(
+    new RgbColor(34, 211, 238),
+    ThemeHarmony.Triadic,
+    contrast: 0.35);
+var house = sheet.Themed(housePalette.ToLayoutTheme());
+
+var value = BlockLayout.Build(house, width: 46);
+var ansi = value.Render(MarkupFormat.Ansi, registry);
+var html = value.Render(MarkupFormat.Html, registry);
+```
+
+![The same MarkupString layout rendered with a fantasy preset and a generated triadic palette](docs/assets/showcase-theming.png)
+
+Use `.Themed(...)` to override the surrounding theme, or `.ThemedUnder(...)` to provide defaults
+that a reader's theme can replace. See [themes and palettes](docs/layout.md#themes-and-palettes) for
+the built-in presets, light and dark modes, custom glyphs, base16 schemes, JSON, and contrast checks.
+
 ## Why MarkupString?
 
 - **One source of truth** — keep content and semantics together, then choose the output format at

docs/showcase/Program.cs

@@ -74,14 +74,77 @@
 		figureValue,
 		registry);
 
+var character = new Stack(
+[
+		new Fields(
+		[
+				new Field(P("Name"), P("Lyra Vale")),
+				new Field(P("Role"), P("Wayfinder")),
+				new Field(P("Region"), P("Glasswood")),
+				new Field(P("Status"), P("Ready")),
+		]) { Columns = 2, Gap = 3, Leader = P("·") },
+		new Rule(P("CURRENT QUEST")),
+		new Gauge(7, 10) { Label = P("Trail"), Show = GaugeShow.Percent },
+		new Bullets([P("Map the moonwell"), P("Return before dawn")]),
+]).Bordered(P("WAYFINDER'S JOURNAL"));
+
+var fantasy = BlockLayout.Build(character.Themed(ThemePalette.Preset("fantasy")!.ToLayoutTheme()), 46);
+var generatedPalette = ThemePalette.Generate(new RgbColor(34, 211, 238), ThemeHarmony.Triadic, contrast: 0.35);
+var generated = BlockLayout.Build(character.Themed(generatedPalette.ToLayoutTheme()), 46);
+WriteThemePage(
+		Path.Combine(output, "theming.html"),
+		"One layout, a whole new world",
+		"Presets and generated palettes recolour every semantic part — and can change the shapes too.",
+		fantasy,
+		generated,
+		registry);
+
 static MarkupText P(string text) => MarkupText.Plain(text);
 
 static void WritePage(string path, string title, string subtitle, MarkupText value, MarkupRegistry registry)
 {
 	var ansi = value.Render(MarkupFormat.Ansi, registry);
 	var ansiForBrowser = AnsiEscapeParser.Parse(ansi).Render(MarkupFormat.Html, registry);
 	var html = value.Render(MarkupFormat.Html, registry);
-	var escapedAnsi = WebUtility.HtmlEncode(ansi.Replace("\u001b", "\\e", StringComparison.Ordinal));
+	WriteComparisonPage(
+			path, title, subtitle, "MarkupText <span>→</span> renderer <span>→</span> native output",
+			"ANSI terminal", "SGR + cells", "terminal", ansiForBrowser,
+			"HTML browser", "semantic elements", "browser", html);
+}
+
+static void WriteThemePage(
+	string path,
+	string title,
+	string subtitle,
+	MarkupText preset,
+	MarkupText generated,
+	MarkupRegistry registry)
+{
+	var presetHtml = AnsiEscapeParser.Parse(preset.Render(MarkupFormat.Ansi, registry)).Render(MarkupFormat.Html, registry);
+	var generatedHtml = AnsiEscapeParser.Parse(generated.Render(MarkupFormat.Ansi, registry)).Render(MarkupFormat.Html, registry);
+	WriteComparisonPage(
+			path, title, subtitle, "layout <span>→</span> palette <span>→</span> themed output",
+			"Fantasy preset", "colours + glyphs", "terminal", presetHtml,
+			"Generated palette", "triadic harmony", "terminal", generatedHtml);
+}
+
+static void WriteComparisonPage(
+	string path,
+	string title,
+	string subtitle,
+	string flowHtml,
+	string leftLabel,
+	string leftNative,
+	string leftClass,
+	string leftContent,
+	string rightLabel,
+	string rightNative,
+	string rightClass,
+	string rightContent)
+{
+	static string PanelBody(string cssClass, string content) => cssClass == "terminal"
+			? "<pre class=\"terminal\">" + content + "</pre>"
+			: "<div class=\"browser\">" + content + "</div>";
 
 	File.WriteAllText(path, $$"""
 <!doctype html>
@@ -117,26 +180,24 @@ static void WritePage(string path, string title, string subtitle, MarkupText val
 .browser .ms-figure-image { max-width: 220px; margin: 0 20px 14px 0; filter: drop-shadow(0 10px 20px rgba(0, 0, 0, .35)); }
 .browser .ms-figure { font-family: "DejaVu Sans", sans-serif; }
 .browser .ms-text { line-height: 1.65; }
-.source { display: none; }
 </style>
 </head>
 <body>
 <main>
   <header>
     <div><h1>{{WebUtility.HtmlEncode(title)}}</h1><p class="subtitle">{{WebUtility.HtmlEncode(subtitle)}}</p></div>
-    <div class="flow">MarkupText <span>→</span> renderer <span>→</span> native output</div>
+    <div class="flow">{{flowHtml}}</div>
   </header>
   <section class="comparison">
     <article class="panel">
-      <div class="panel-head"><i class="dot"></i><span class="label">ANSI terminal</span><span class="native">SGR + cells</span></div>
-      <pre class="terminal">{{ansiForBrowser}}</pre>
+      <div class="panel-head"><i class="dot"></i><span class="label">{{WebUtility.HtmlEncode(leftLabel)}}</span><span class="native">{{WebUtility.HtmlEncode(leftNative)}}</span></div>
+      {{PanelBody(leftClass, leftContent)}}
     </article>
     <article class="panel">
-      <div class="panel-head"><i class="dot"></i><span class="label">HTML browser</span><span class="native">semantic elements</span></div>
-      <div class="browser">{{html}}</div>
+      <div class="panel-head"><i class="dot"></i><span class="label">{{WebUtility.HtmlEncode(rightLabel)}}</span><span class="native">{{WebUtility.HtmlEncode(rightNative)}}</span></div>
+      {{PanelBody(rightClass, rightContent)}}
     </article>
   </section>
-  <pre class="source">{{escapedAnsi}}</pre>
 </main>
 </body>
 </html>

docs/showcase/README.md

@@ -1,6 +1,6 @@
 # README showcase captures
 
-The two README screenshots are generated from MarkupString values rather than recreated by hand.
+The README screenshots are generated from MarkupString values rather than recreated by hand.
 The checked-in captures use this supported Linux x64 environment:
 
 - the .NET SDK selected by the repository's `global.json`;
@@ -23,7 +23,9 @@ present. After restoring the repository once, run from its root:
 docs/showcase/capture.sh
 ```
 
-Each page places the same value's ANSI rendering beside its semantic HTML rendering. The ANSI side
-is parsed back only to make its terminal styling visible in the browser capture; its text and SGR
-styling come from `Render(MarkupFormat.Ansi)`. The capture script applies rounded alpha masks and
-transparent padding so the dark cards sit cleanly on both GitHub README themes.
+The format pages place the same value's ANSI rendering beside its semantic HTML rendering. The
+theme page places the same layout under a preset and a generated palette. ANSI is parsed back only
+to make its terminal styling visible in the browser capture; its text and SGR styling come from
+`Render(MarkupFormat.Ansi)`. The capture script applies rounded alpha masks and transparent padding
+so the dark cards sit cleanly on both GitHub README themes, and omits volatile PNG timestamps so a
+repeat capture is byte-for-byte identical.

docs/showcase/capture.sh

@@ -58,8 +58,10 @@ capture() {
         "$raw"
 
     magick composite -compose CopyOpacity "$mask" "$raw" "$clipped"
-    magick "$clipped" -bordercolor none -border 18 "$asset_dir/$asset"
+    magick "$clipped" -bordercolor none -border 18 \
+        -define png:exclude-chunk=date,time "$asset_dir/$asset"
 }
 
 capture box-drawing.html showcase-box-drawing.png
 capture image-drawing.html showcase-image-drawing.png
+capture theming.html showcase-theming.png