Not just plain text: rendering Markdown in Compose

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NOTJUST PLAINTEXT RENDERING MARKDOWN IN COMPOSE Sebastiano Poggi @sebastiano.dev @seb@androiddev.social

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HAS THIS EVER HAPPENED TO YOU?

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“I want to display rich text in this label” — You, a fancy cursive-speaking person

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Reticulate splines Enable spline reticulation algorithms Learn more “I want to display rich text in this label” — You, a fancy cursive-speaking person

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Web HTML & CSS

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Web HTML & CSS Swing HTML & CSS

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Web HTML & CSS Swing HTML & CSS **

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Web HTML & CSS Swing HTML & CSS ** Android views HTML, to some extent

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Web HTML & CSS Swing HTML & CSS ** Android views HTML, to some extent Jetpack Compose HTML, to some extent

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Web HTML & CSS Swing HTML & CSS ** Android views HTML, to some extent Jetpack Compose HTML, to some extent Compose for Desktop Well, err… DIY

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WE CAN DO BETTER

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Small detour

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** HTML & CSS

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** a lot of heavy lifting

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https://www.codewiththeitalians.it/

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https://www.codewiththeitalians.it/

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https://www.codewiththeitalians.it/ Fix with CSS! overflow-wrap: break-word;

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https://www.codewitht heitalians.it/ overflow-wrap: break-word; Fix with CSS!

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overflow-wrap: break-word; …does not work https://www.codewiththeitalians.it/ Fix with CSS!

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What do we do, then?

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IF YOU GUESSED HERE’S YOUR TROPHY ! HACKS What do we do, then?

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Inject strategically https://www.codewiththeitalians.it/

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https://www.codewiththeitalians.it/ Inject strategically

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https://www. codewiththeitalians.it/ Inject strategically

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https://www.codewitht heitalians.it/ EVERYTHING IS A LIE Inject strategically

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DO NOT WANT /end of detour

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WHAT DO WE DO? MARKDOWN maybe slightly spoiled by the talk title

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Why Markdown Easy to read and write Does not allow users to de!ne styling Good for my use case ! Great for UI text and i18n

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Why Markdown Easy to read and write Does not allow users to de!ne styling Good for my use case ! Great for UI text and i18n

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Hello world!"font>

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Hello world!"font> Hello world

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Hello world!"font> Hello world

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world Hello world Hello world!"font>

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world Hello world Hello world!"font>

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Hello world Hello world!"font>

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Can’t happen in Markdown!

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Can’t happen in Markdown! bold strong emphasis

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Hello **world**

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Hello **world** Hello world!"strong>

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Hello **world** Hello world Hello world!"strong>

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Hello **world** Hello world Hello world!"strong>

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Hello **world** Hello world Hello world!"strong>

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Hello **world** Hello world Hello world!"strong>

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WE WANT NORMAL

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WHAT IS NORMAL, ANYWAY?

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what’s expected normal

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what’s expected normal

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GitHub GitLab Issue trackers Google Docs Blog post composers StackOver"ow …and more

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Intuitive expectations GitHub GitLab Issue trackers Google Docs Blog post composers StackOver"ow …and more

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Intuitive expectations MARKDOWN IS A LIE

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Time for another rabbit hole? "

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John Gruber’s Daring Fireball — 2004

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John Gruber’s Daring Fireball — 2004 Loves Apple Tech opinionist

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John Gruber’s Daring Fireball — 2004 Reference parser The spec lives here (intentionally) Vague

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Reference parser …written in Perl

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Reference parser …written in Perl “write-only language”

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Markdown specs are limited

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Missing “expected” features: Tables Syntax highlighting Emojis Footnotes Strikethrough …

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VAGUE SPECS MISSING FEATURES BAD REFERENCE # "

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Many incompatible implementations

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Many incompatible implementations Babelmark

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Many incompatible implementations GitHub Flavored Markdown

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Many incompatible implementations GFM

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What is the !x?

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No content

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COMMONMARK Born in 2014 as Standard Markdown

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CommonMark GFM GLFM StackOver"ow …

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“FUN” FACT GFM is also poorly specced Features de!ned in docs but not specs

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HOWEVER For many Markdown is ~GFM CommonMark has a nice parser

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Let’s use CommonMark! commonmark-java, not jetbrains/markdown

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Let’s use CommonMark! commonmark-java, not jetbrains/markdown Kotlin-based, extensible Missing GFM features Not fully compliant

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Let’s use CommonMark! commonmark-java, not jetbrains/markdown Java-based, extensible GFM extensions Fully compliant

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HOW TO RENDER MARKDOWN IN TWO EASY* STEPS

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Small detour

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Jewel Compose for Desktop theme & components code lives here

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End of detour

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MARKDOWN

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MARKDOWN ...how?

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Raw MarkDown Parse as AST Emit UI components Raw Markdown

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Raw MarkDown Parse as AST Emit UI components step 1 step 2 Raw Markdown

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Step 1: Parse as AST commonmark-java AST

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Step 1: Parse as AST commonmark-java AST outside the composition

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Block Block Block Block …

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Block Block Block Block … Block Block or Inline node Inline node … …

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Can’t use CommonMark models as-is No equals() and hashCode() No random access to children

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Parse as AST List ✅

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Step 2a: Render block nodes Step 2b: Render inline nodes Step 2: Emit UI components

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Step 2a: Render block nodes Step 2b: Render inline nodes Step 2: Emit UI components inside the composition

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Step 2a: Render block nodes Step 2b: Render inline nodes inside the composition

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Step 2a: Render block nodes Step 2b: Render inline nodes inside the composition MarkdownBlocks composables

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Block Block … Block … Block How do we handle nested blocks? Block

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RECURSION $

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Blockquote Bullet list Paragraph Header 1 Image Divider Paragraph Code block Paragraph … … Simple item Complex item …

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Paragraph … Blockquote Complex item Simple item … Bullet list Paragraph Header 1 Image Divider Paragraph Code block … render( )

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Blockquote Paragraph … Complex item Simple item … Bullet list Paragraph Header 1 Image Divider Paragraph Code block … render( )

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Blockquote Paragraph … Blockquote Complex item Simple item … Bullet list Paragraph Header 1 Image Divider Paragraph Code block … render( )

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Blockquote Paragraph Header 1 Image Divider Paragraph Code block … Paragraph … Complex item Simple item … Bullet list render( render( )

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Blockquote Paragraph Header 1 Image Divider Paragraph Code block … Paragraph … Complex item Simple item … Bullet list render( render( )

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YEAH BUT ACTUALLY WHAT ABOUT HTML?

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No HTML. Don’t want to implement a browser

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No HTML. Don’t want to implement a browser May have special casing

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Step 2a: Step 2b: Render inline nodes ✅ Render block nodes

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Paragraph Inline node Inline node … No recursion needed %

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Step 2a: Render block nodes InlineMarkdown inside the composition AnnotatedString Step 2b: Render inline nodes

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WE HAVE A PROBLEM AnnotatedString

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WE HAVE A PROBLEM AnnotatedString limited by TextStyle capabilities

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Case study: inline code RAW MARKDOWN RENDERED MARKDOWN This PR adds animations to the `Onboarding` flow.

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Case study: inline code RAW MARKDOWN RENDERED MARKDOWN This PR adds animations to the Onboarding "ow. This PR adds animations to the `Onboarding` flow.

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Case study: inline code This PR adds animations to the `Onboarding` flow. RAW MARKDOWN This PR adds animations to the Onboarding "ow. RENDERED MARKDOWN Onboa &

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Case study: inline code This PR adds animations to the `Onboarding` flow. RAW MARKDOWN RENDERED MARKDOWN This PR adds animations to the Onboarding "ow. Onboardin '

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Case study: inline code I reckon you could improve it by using `animateFloatAsState(target, tween(1000, 1500))` ! RAW MARKDOWN RENDERED MARKDOWN I reckon you could improve it by using animateFloatAsState (target, tween(1000, 1500)) ! (

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inline images and links

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inline images and links doable, but wip InlineTextContent Coil for loading Layout jumps unavoidable

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inline images and links Use LinkAnnotation Stateful styling Can’t draw focus ring

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inline images and links Use LinkAnnotation Stateful styling Can’t draw focus ring Reticulate splines Enable spline reticulation algorithms Learn more

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IT WILL GET BETTER (I hope)

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PUTTING IT ALL TOGETHER

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Two-pass processing: Parse as AST Emit UI components

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Two-pass processing: Parse as AST Parse as AST Emit UI components Emit UI components Outside the composition Run only when raw Markdown changes

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Two-pass processing: Parse as AST Emit UI components Outside the composition Run only when raw Markdown changes Inside the composition Run when raw Markdown changes Run when theme changes Run when editor scheme changes Builds AnnotatedStrings: expensive?

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Display rich text Render large !le vs

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Display rich text Render large !le vs many small instances minimise overhead

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Display rich text Render large !le vs many small instances lazy container editor mode minimise overhead

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Display rich text Render large !le vs many small instances lazy container editor mode scroll sync (wip) minimise overhead

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ONE LAST THING ) ☝️

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WYSIWYG is not possible

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LET’S SEE THIS IN ACTION

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No content

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Good enough* to render its readme Has missing/WIP features Extensible: GFM features

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I SWEAR THIS IS ALMOST OVER

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Forked by OpenAI for ChatGPT Android A HAT TIP TO https://halilibo.com/compose-richtext/ the one from the keynote

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The OG Markdown renderer inspo ANOTHER HAT TIP TO https://github.com/ErikHellman/MarkdownComposer

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SO WHAT I MEANT TO SAY ALL ALONG IS…

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Markdown is great Especially for i18n and server-driven UI Try out Markdown in Jewel …or make your own renderer

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THANK YOU ♥️ @sebastiano.dev @seb@androiddev.social