Enable auto-scaling features in theme metadata explicitly

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Breaking
+
+- Change auto-scaling features to require enabling by `@auto-scaling` metadata of theme CSS explicitly ([#81](https://github.com/marp-team/marp-core/pull/81))
+
 ### Changed
 
 - Upgrade Marpit to [v0.9.0](https://github.com/marp-team/marpit/releases/v0.9.0) ([#80](https://github.com/marp-team/marp-core/pull/80))

README.md

@@ -121,9 +121,29 @@ $$
 </tbody>
 </table>
 
-### Auto scaling features
+### Auto-scaling features
 
-Auto scaling is available only if enabled [Marpit's `inlineSVG` mode](https://github.com/marp-team/marpit#inline-svg-slide-experimental). You have to run [`Marp.ready()`](#marpready) on browser context.
+Auto-scaling is available only if enabled [Marpit's `inlineSVG` mode](https://github.com/marp-team/marpit#inline-svg-slide-experimental) and defined `@auto-scaling` meta data in an using theme CSS. In addition, you have to run [`Marp.ready()`](#marpready) on browser context.
+
+```css
+/*
+ * @theme enable-all-auto-scaling
+ * @auto-scaling true
+ */
+```
+
+Marp Core's scaling features will be realized by manipulating the original DOM to use inline SVG. So the theme author must take care of updated DOM in styling. Refer to [the source code of offical themes][themes].
+
+`@auto-scaling` meta can also pick the favorite features to enable by using keyword(s).
+
+```css
+/*
+ * @theme enable-auto-scaling-for-fitting-header-and-math
+ * @auto-scaling fittingHeader,math
+ */
+```
+
+> :warning: In the math block and the code block, Marp Core won't detect whether they actually protrude from the slide. It might not work scaling correctly when there are many elements in a slide.
 
 #### Fitting header
 
@@ -135,27 +155,29 @@ When the headings contains `<!-- fit -->` comment, the size of headings will res
 
 This syntax is similar to [Deckset's `[fit]` keyword](https://docs.decksetapp.com/English.lproj/Formatting/01-headings.html), but we use HTML comment to hide a fit keyword on Markdown rendered as document.
 
+> :information_source: `@auto-scaling fittingHeader` is a keyword of the `@auto-scaling` meta to enable fitting header.
+
 #### Math block
 
 We can scale-down the viewing size of math block (surrounded by `$$`) to fit a slide automatically.
 
-|              Traditional rendering               |              Auto scaling               |
+|              Traditional rendering               |              Auto-scaling               |
 | :----------------------------------------------: | :-------------------------------------: |
-| ![Traditional rendering](https://bit.ly/2NXoHuW) | ![Auto scaling](https://bit.ly/2M6LyCk) |
+| ![Traditional rendering](https://bit.ly/2NXoHuW) | ![Auto-scaling](https://bit.ly/2M6LyCk) |
 
-#### Code block (Only for `default` and `gaia` theme)
+> :information_source: `@auto-scaling math` is a keyword of the `@auto-scaling` meta to enable math block scaling.
+
+#### Code block
 
 Several themes also can scale-down the viewing size of the code block to fit a slide.
 
-|              Traditional rendering               |              Auto scaling               |
+|              Traditional rendering               |              Auto-scaling               |
 | :----------------------------------------------: | :-------------------------------------: |
-| ![Traditional rendering](https://bit.ly/2LyEnmi) | ![Auto scaling](https://bit.ly/2N4yWQZ) |
+| ![Traditional rendering](https://bit.ly/2LyEnmi) | ![Auto-scaling](https://bit.ly/2N4yWQZ) |
 
 These features means that the contents on a slide are not cropped, and not shown unnecessary scrollbars in code.
 
-> :information_source: `uncover` theme has disabled scaling for code block because we use elastic style that has not compatible with it.
-
-> :warning: We won't detect whether the math and code block actually protrudes from the slide. It might not work scaling correctly when there are many elements in a slide.
+> :information_source: `@auto-scaling code` is a keyword of the `@auto-scaling` meta to enable code block scaling. `uncover` theme has disabled code block scaling because we use elastic style that has not compatible with it.
 
 ## Constructor options
 

package.json

@@ -90,7 +90,7 @@
     "typescript": "^3.3.3333"
   },
   "dependencies": {
-    "@marp-team/marpit": "^0.9.0",
+    "@marp-team/marpit": "^0.9.1",
     "@marp-team/marpit-svg-polyfill": "^0.3.0",
     "emoji-regex": "^8.0.0",
     "highlight.js": "^9.15.6",

src/fitting/fitting.ts

@@ -1,6 +1,7 @@
 import marpitPlugin from '@marp-team/marpit/lib/markdown/marpit_plugin'
 import fittingCSS from './fitting.scss'
 import { Marp } from '../marp'
+import { getThemeMeta } from '../theme'
 
 export const css = fittingCSS
 export const attr = 'data-marp-fitting'
@@ -9,41 +10,35 @@ export const math = 'data-marp-fitting-math'
 export const svgContentAttr = 'data-marp-fitting-svg-content'
 export const svgContentWrapAttr = 'data-marp-fitting-svg-content-wrap'
 
-export type ThemeResolver = () => string | undefined
+const codeMatcher = /^(<pre[^>]*?><code[^>]*?>)([\s\S]*)(<\/code><\/pre>\n*)$/
 
-function wrapTokensByFittingToken(token, tokens: any[]): any[] {
-  const open = new token('marp_fitting_open', 'span', 1)
-  open.attrSet(attr, 'plain')
-
-  return [open, ...tokens, new token('marp_fitting_close', 'span', -1)]
+const isEnabledAutoScaling = (marp: Marp, key?: string): boolean => {
+  const meta = getThemeMeta(marp, 'auto-scaling') || ''
+  return !!(meta === 'true' || (key && meta.includes(key)))
 }
 
 // Wrap code block and fence renderer by fitting elements.
-function fittingCode(md, themeResolver: ThemeResolver): void {
+function fittingCode(md): void {
   const { code_block, fence } = md.renderer.rules
 
-  const codeMatcher = /^(<pre[^>]*?><code[^>]*?>)([\s\S]*)(<\/code><\/pre>\n*)$/
-
   const replacedRenderer = func => (...args) => {
     const rendered: string = func(...args)
 
-    const { fittingCode } = md.marpit.themeSet.getThemeProp(
-      themeResolver()!,
-      'meta'
-    )
-    if (fittingCode === 'false') return rendered
+    if (isEnabledAutoScaling(md.marpit, 'code')) {
+      return rendered.replace(codeMatcher, (_, start, content, end) => {
+        if (md.marpit.options.inlineSVG) {
+          return [
+            `${start}<svg ${attr}="svg" ${code}><foreignObject>`,
+            `<span ${svgContentAttr}><span ${svgContentWrapAttr}>`,
+            content,
+            `</span></span></foreignObject></svg>${end}`,
+          ].join('')
+        }
+        return `${start}<span ${attr}="plain">${content}</span>${end}`
+      })
+    }
 
-    return rendered.replace(codeMatcher, (_, start, content, end) => {
-      if (md.marpit.options.inlineSVG) {
-        return [
-          `${start}<svg ${attr}="svg" ${code}><foreignObject>`,
-          `<span ${svgContentAttr}><span ${svgContentWrapAttr}>`,
-          content,
-          `</span></span></foreignObject></svg>${end}`,
-        ].join('')
-      }
-      return `${start}<span ${attr}="plain">${content}</span>${end}`
-    })
+    return rendered
   }
 
   md.renderer.rules.code_block = replacedRenderer(code_block)
@@ -71,10 +66,14 @@ function fittingHeader(md): void {
           }
 
           if (requireWrapping) {
-            token.children = wrapTokensByFittingToken(
-              state.Token,
-              token.children
-            )
+            const open = new state.Token('marp_fitting_open', 'span', 1)
+            open.attrSet(attr, 'plain')
+
+            token.children = [
+              open,
+              ...token.children,
+              new state.Token('marp_fitting_close', 'span', -1),
+            ]
           }
         } else if (token.type === 'heading_close') {
           target = undefined
@@ -83,39 +82,47 @@ function fittingHeader(md): void {
     }
   })
 
-  if (md.marpit.options.inlineSVG) {
-    Object.assign(md.renderer.rules, {
-      marp_fitting_open: () =>
-        `<svg ${attr}="svg"><foreignObject><span ${svgContentAttr}>`,
-      marp_fitting_close: () => '</span></foreignObject></svg>',
-    })
-  }
+  md.renderer.rules.marp_fitting_open = () =>
+    isEnabledAutoScaling(md.marpit, 'fittingHeader')
+      ? md.marpit.options.inlineSVG
+        ? `<svg ${attr}="svg"><foreignObject><span ${svgContentAttr}>`
+        : `<span ${attr}="plain">`
+      : ''
+
+  md.renderer.rules.marp_fitting_close = () =>
+    isEnabledAutoScaling(md.marpit, 'fittingHeader')
+      ? `</span>${md.marpit.options.inlineSVG ? '</foreignObject></svg>' : ''}`
+      : ''
 }
 
 function fittingMathBlock(md): void {
   const { marp_math_block } = md.renderer.rules
   if (!marp_math_block) return
 
-  const replacedRenderer = func => (...args) => {
+  md.renderer.rules.marp_math_block = (...args) => {
     // Rendered math block is wrapped by `<p>` tag in math plugin
-    const katex: string = func(...args).slice(3, -4)
-
-    if (md.marpit.options.inlineSVG) {
-      return [
-        `<p><svg ${attr}="svg" ${math}><foreignObject>`,
-        `<span ${svgContentAttr}><span ${svgContentWrapAttr}>`,
-        katex,
-        `</span></span></foreignObject></svg></p>`,
-      ].join('')
+    const rendered: string = marp_math_block(...args)
+
+    if (isEnabledAutoScaling(md.marpit, 'math')) {
+      const katex = rendered.slice(3, -4)
+
+      if (md.marpit.options.inlineSVG) {
+        return [
+          `<p><svg ${attr}="svg" ${math}><foreignObject>`,
+          `<span ${svgContentAttr}><span ${svgContentWrapAttr}>`,
+          katex,
+          `</span></span></foreignObject></svg></p>`,
+        ].join('')
+      }
+      return `<p><span ${attr}="plain">${katex}</span></p>`
     }
-    return `<p><span ${attr}="plain">${katex}</span></p>`
-  }
 
-  md.renderer.rules.marp_math_block = replacedRenderer(marp_math_block)
+    return rendered
+  }
 }
 
-export const markdown = marpitPlugin((md, themeResolver: ThemeResolver) => {
+export const markdown = marpitPlugin(md => {
   md.use(fittingHeader)
-  md.use(fittingCode, themeResolver)
-  md.use(fittingMathBlock)
+    .use(fittingCode)
+    .use(fittingMathBlock)
 })

src/marp.ts

@@ -74,10 +74,7 @@ export class Marp extends Marpit {
     md.use(htmlPlugin.markdown)
       .use(emojiPlugin.markdown)
       .use(mathPlugin.markdown, flag => (this.renderedMath = flag))
-      .use(
-        fittingPlugin.markdown,
-        () => (this.lastGlobalDirectives || {}).theme
-      )
+      .use(fittingPlugin.markdown)
   }
 
   highlighter(code: string, lang: string): string {

src/theme.ts

@@ -0,0 +1,8 @@
+import Marp from './marp'
+
+export function getThemeMeta(marp: Marp, meta: string): string | undefined {
+  const { lastGlobalDirectives } = marp as any
+  const theme = lastGlobalDirectives ? lastGlobalDirectives.theme : undefined
+
+  return marp.themeSet.getThemeProp(theme, `meta.${meta}`)
+}

test/marp.ts

@@ -492,7 +492,7 @@ describe('Marp', () => {
         expect($('pre').text()).toContain('CODE BLOCK')
       })
 
-      it('does not wrap by svg when specified theme has fittingCode meta as false', () => {
+      it('does not wrap by svg when specified uncover theme', () => {
         const instance = marp()
         const theme = instance.themeSet.get('uncover')!
         theme.meta.fittingCode = 'false'

themes/README.md

@@ -1,6 +1,6 @@
-# Marp-core built-in themes
+# Marp Core built-in themes
 
-We provide some nice official themes in marp-core. You can choose a favorite theme by using [Marpit `theme` directive](https://marpit.marp.app/directives?id=theme) in your Markdown.
+We provide some nice official themes in Marp Core. You can choose a favorite theme by using [Marpit `theme` directive](https://marpit.marp.app/directives?id=theme) in your Markdown.
 
 Screenshots were taken from the rendered result of [an example][example].
 
@@ -14,6 +14,8 @@ The all of built-in themes support `invert` class to use the inverted color sche
 <!-- class: invert -->
 ```
 
+---
+
 ## Default
 
 [![](https://user-images.githubusercontent.com/3993388/48039490-53be1b80-e1b8-11e8-8179-0e6c11d285e2.png)][example]
@@ -101,4 +103,23 @@ Uncover theme has three design concepts: simple, minimal, and modern. It's inspi
 
 ### :warning: Restrictions
 
-[Auto scaling for code block](https://github.com/marp-team/marp-core#auto-scaling-features) is disabled because uncover theme uses the elastic style that has not compatible with it.
+[Auto-scaling for code block](https://github.com/marp-team/marp-core#auto-scaling-features) is disabled because uncover theme uses the elastic style that has not compatible with it.
+
+---
+
+## Metadata for additional features
+
+Marp Core will recognize the metadata to be able to enable extra features whose side effect through manipulation to rendered DOM structure.
+
+In other words, the enabled feature requires taking care of manipulated DOM when styling.
+
+### `@auto-scaling`
+
+Enable [auto-scaling features](https://github.com/marp-team/marp-core#auto-scaling-features).
+
+- `true`: Enable all features.
+- `fittingHeader`: Enable fitting header.
+- `math`: Enable scaling for math block.
+- `code`: Enable scaling for code block.
+
+Through separating by comma, it can select multiple keywords for individual features. (e.g. `@auto-scaling fittingHeader,math`)

themes/default.scss

@@ -2,6 +2,9 @@
  * Marp default theme.
  *
  * @theme default
+ * @author Yuki Hattori
+ *
+ * @auto-scaling true
  */
 
 @import '~github-markdown-css';

themes/gaia.scss

@@ -3,6 +3,8 @@
  *
  * @theme gaia
  * @author Yuki Hattori
+ *
+ * @auto-scaling true
  */
 
 $color-light: #fff8e1;

themes/uncover.scss

@@ -3,7 +3,8 @@
  *
  * @theme uncover
  * @author Yuki Hattori
- * @fittingCode false
+ *
+ * @auto-scaling fittingHeader,math
  */
 
 @mixin color-scheme($bg: #fdfcff, $text: #202228, $highlight: #009dd5) {

yarn.lock

@@ -302,13 +302,14 @@
   dependencies:
     detect-browser "^4.1.0"
 
-"@marp-team/marpit@^0.9.0":
-  version "0.9.0"
-  resolved "https://registry.yarnpkg.com/@marp-team/marpit/-/marpit-0.9.0.tgz#5a12f00a97832907806af81933d8d2f5e25cb4e6"
-  integrity sha512-nPtIXu2leY/EDKsjvu3g4tsa98yRAXpM1w2bpUUKLtPC0wirdhxIJWGjW8W24Hm0+c+F/f3jibE7B15fTCVweA==
+"@marp-team/marpit@^0.9.1":
+  version "0.9.1"
+  resolved "https://registry.yarnpkg.com/@marp-team/marpit/-/marpit-0.9.1.tgz#6d25110b370f079378a0ef153776b3aa3d891163"
+  integrity sha512-+60TACjL4M/dGP9KG5WJse1iLbaD4RAMkBpCq7qfwm7JU730WjM6zdTfSXJ6U2o6U/yoJsaDq5UYJ4MNGMwRMA==
   dependencies:
     color-string "^1.5.3"
     js-yaml "^3.13.0"
+    lodash.get "^4.4.2"
     lodash.kebabcase "^4.1.1"
     markdown-it "^8.4.2"
     markdown-it-front-matter "^0.1.2"