Novolis.Markup.Mermaid.Rendering

name: Mermaid Rendering package overview: Add Novolis.Markup.Mermaid.Rendering in novolis-markup with IMermaidable extension methods for SVG (Mermaider) and PNG (Svg.Skia), then thin Avalonia.Mermaid to consume it instead of owning Mermaider. todos:

• id: scaffold-pkg

content: Scaffold Novolis.Markup.Mermaid.Rendering csproj, packages.json, slnx, Directory.Packages.props (Mermaider + Svg.Skia) status: completed

• id: svg-png-api

content: Implement MermaidSvgRenderer, MermaidPngRenderer, MermaidRenderTheme, IMermaidable extension methods status: completed

• id: unit-tests

content: Add Markup.Unit Rendering tests for SVG/PNG/export/themes status: completed

• id: docs-map

content: Package README + Generate-Platform-Slnx.ps1 regen status: completed

• id: avalonia-thin

content: "After markup GPR: Avalonia.Mermaid wraps Rendering; drop direct Mermaider ref" status: completed isProject: false

Context

• There is no Mermaid base class. Diagrams implement `IMermaidable`; emit via `GetMermaidString()`.
• SVG rendering already lives in Avalonia as `MermaidSvg` (Mermaider RenderSvg only — no PNG).
• Naming precedent: `Novolis.Markup.Markdown.Rendering` — Avalonia-free export beside the fluent builder.

Package

Public API

Extensions on IMermaidable (and parallel string helpers for raw Mermaid source):

using Novolis.Markup.Mermaid;
using Novolis.Markup.Mermaid.Rendering;

var chart = new Flowchart(Direction.TopToBottom);
// ...
string? svg = chart.ToSvg();                    // Mermaider
byte[]? png = chart.ToPng(scale: 2f);           // Mermaider → Svg.Skia
chart.ExportSvg(@"d:\out\diagram.svg");
chart.ExportPng(@"d:\out\diagram.png");

Supporting types (moved/adapted from Avalonia):

• MermaidRenderTheme — StudioDark / GitHubLight (same palettes as current MermaidTheme)
• MermaidSvgRenderer — static TryRenderSvg / theme→RenderOptions (core of today’s MermaidSvg)
• MermaidPngRenderer — SVG string → PNG bytes via SKSvg
• MermaidRenderExtensions — ToSvg / ToPng / ExportSvg / ExportPng on IMermaidable
• Soft-fail: Try* / To* return null on blank/invalid (match Avalonia); Export* return bool

HTML <img> / fallback <pre> stay in Avalonia (UI host concern), not this package.

flowchart LR
  builder[IMermaidable]
  text[Mermaid source string]
  mermaider[Mermaider RenderSvg]
  svg[SVG string]
  skia[Svg.Skia]
  png[PNG bytes]
  builder -->|GetMermaidString| text
  text --> mermaider --> svg
  svg --> skia --> png

Avalonia follow-up (same effort, after markup publish)

In `novolis-avalonia`:

• Replace direct Mermaider PackageReference with Novolis.Markup.Mermaid.Rendering
• Make MermaidSvg.TryRenderSvg / OptionsFor thin wrappers over MermaidSvgRenderer
• Map MermaidTheme ↔ MermaidRenderTheme (keep Avalonia enum for API stability; Markdown preview mapping unchanged)
• Update unit tests that assert theme options

Publish order: markup first (GPR), then Avalonia. Local ProjectRef via Novolis.Platform.slnx covers both before GPR.

Repo wiring (novolis-markup)

• Add project to `Novolis.Markup.slnx`
• Register in `.novolis/packages.json`
• Central versions in `Directory.Packages.props`: Mermaider, Svg.Skia
• ProjectReference from `Novolis.Markup.Unit`
• Package README (brand header + quick start, mirror Markdown.Rendering)
• Regen platform map: pwsh -File d:\novolis\novolis-governance\build\Generate-Platform-Slnx.ps1

Tests

Under tests/Novolis.Markup.Unit/Mermaid/Rendering/:

• Flowchart/sequence ToSvg contains <svg
• Blank / invalid → null
• ToPng non-empty, PNG signature 89 50 4E 47
• Theme StudioDark vs GitHubLight changes background options
• ExportSvg / ExportPng write files

Out of scope

• Dogfooding demo app
• Changing fluent Mermaid builders
• Moving HTML image helpers into Markup
• Touching Novolis.Rendering.* GPU stack