Add feature detection for WebKit

README.md

@@ -12,7 +12,7 @@ The polyfill for [the inline SVG slide][inline-svg] rendered by [Marpit].
 
 ### Supported browser
 
-- [WebKit](#webkit) based browser: Safari and iOS browsers (included Chrome and Firefox)
+- [WebKit](#webkit) based browser: Safari and iOS browsers (including iOS Chrome, iOS Firefox, iOS Edge, and so on...)
 
 ## Usage
 
@@ -36,13 +36,22 @@ The polyfill for [the inline SVG slide][inline-svg] rendered by [Marpit].
 
 [Marpit]'s [inline SVG slide][inline-svg] has a lot of advantages: No requires JavaScript, gives better performance for scaling, and has predicatable DOM structure.
 
-But unfortunately, WebKit browser has not scaled the wrapped HTML correctly. It is caused from a long standing [bug 23113](https://bugs.webkit.org/show_bug.cgi?id=23113), and it does not resolved in the last 10 years.
+But unfortunately, WebKit browser has not scaled the wrapped HTML correctly. It is caused from a long standing [bug 23113](https://bugs.webkit.org/show_bug.cgi?id=23113), and it does not resolved in the last 15 years.
 
 ![](https://raw.githubusercontent.com/marp-team/marpit-svg-polyfill/main/docs/webkit-bug.png)
 
-Through inspector, we have not confirmed that there is a wrong layout in SVG itself and around. Thus, the problem has in a rendering of the parent SVG.
-
-Actually, the nested SVG seems to be scaled correctly (e.g. `<!--fit-->` keyword in [Marp Core](https://github.com/marp-team/marp-core)).
+> **Note**
+> A brand-new SVG engine for WebKit called as [**"Layer-based SVG engine (LBSE)"**](https://blogs.igalia.com/nzimmermann/posts/2021-10-29-layer-based-svg-engine/) is currently under development, and it will finally bring glitch-free scaling without JS. (See also: [Status of the new SVG engine in WebKit](https://wpewebkit.org/blog/05-new-svg-engine.html))
+>
+> You can test LBSE in [Safari Technology Preview](https://developer.apple.com/safari/technology-preview/) by following these steps:
+>
+> 1. Install Safari Technology Preview
+> 1. Run `defaults write com.apple.SafariTechnologyPreview IncludeInternalDebugMenu 1` in terminal
+> 1. Open Safari Technology Preview
+> 1. Turn on **"Layer-based SVG engine (LBSE)"** from "Debug" menu → "WebKit Internal Features"
+> 1. Restart app
+>
+> marpit-svg-polyfill v2.1.0 and later will try to detect whether or not enabled LBSE, and does not apply polyfill if LBSE was available.
 
 ## Solutions
 
@@ -55,23 +64,32 @@ We try to simulate scaling and centering by applying `transform` / `transform-or
 ```html
 <svg viewBox="0 0 1280 960">
   <foreignObject width="1280" height="960">
-    <section
-      style="transform-origin:0 0;transform:translate(123px,456px) scale(0.36666);"
-    >
+    <section style="transform-origin:0 0;transform:matrix(......);">
       ...
     </section>
   </foreignObject>
 </svg>
 ```
 
-We have to get the computed size of SVG element, so the polyfill would make a sacrifice of zero-JS feature.
+marpit-svg-polyfill uses the result of `getScreenCTM()` method, so the polyfill will sacrifice "zero-JS slide", the key feature of inline SVG.
 
 #### Repainting
 
-WebKit browser would not trigger repainting even if modified the contents of slide. It becomes a problem when supporting the live preview feature in [Marp Web](https://web.marp.app/).
+WebKit browser would not trigger repainting even if modified the contents of slide. It becomes a problem when supporting the live preview feature in Marp tools.
 
 Fortunately, [a genius already resolved this problem only in CSS!](https://stackoverflow.com/a/21947628) `transform:translateZ(0)` would trigger re-painting immidiately when modified contents.
 
+#### Animation GIF
+
+People like to put GIF animation in the slide. However, GIF in polyfilled slides have glitches. GIF updates only a cropped part somewhere.
+
+Applying `transform:translateZ(0.0001px)` to each `<section>` elements within SVG is a magic to resolve that. 🪄
+
+> **Warning**
+> This style brings slightly blurred contents too. Our polyfill prefers to render animated contents correctly.
+
+<!--
+
 ## Advanced
 
 ### Apply polyfill manually
@@ -97,6 +115,8 @@ We have confirmed a similar rendering bug to WebKit in a few Blink based browser
 
 We are not applied polyfill for Blink browsers because [they are working toward to resolve this.](https://bugs.chromium.org/p/chromium/issues/detail?id=467484) But you may apply `webkit()` manually if you required.
 
+-->
+
 ## Contributing
 
 We are following [the contributing guideline of marp-team projects](https://github.com/marp-team/.github/blob/master/CONTRIBUTING.md). Please read these guidelines this before starting work in this repository.

package.json

@@ -43,6 +43,9 @@
     "preset": "ts-jest",
     "restoreMocks": true,
     "testEnvironment": "jest-environment-jsdom",
+    "testEnvironmentOptions": {
+      "resources": "usable"
+    },
     "testMatch": [
       "<rootDir>/test/**/!(@(.|_))*.[jt]s"
     ]
@@ -81,6 +84,7 @@
     "@types/node": "^18.11.19",
     "@typescript-eslint/eslint-plugin": "^5.50.0",
     "@typescript-eslint/parser": "^5.50.0",
+    "canvas": "^2.11.0",
     "eslint": "^8.33.0",
     "eslint-config-prettier": "^8.6.0",
     "eslint-plugin-import": "^2.27.5",

src/polyfill.ts

@@ -1,10 +1,25 @@
+import { isRequiredPolyfill } from './utils/feature-detection'
+
 const msgPrefix = 'marpitSVGPolyfill:setZoomFactor,'
 
-export type PolyfillOption = { target?: ParentNode }
+type PolyfillsRawArray = Array<(opts: PolyfillOption) => void>
+type PolyfillsArray = PolyfillsRawArray & PromiseLike<PolyfillsRawArray>
+
+export type PolyfillOption = {
+  /** The parent node to observe. It's useful for observing Marpit slides inside shadow DOM. */
+  target?: ParentNode
+}
 
 export const observerSymbol = Symbol()
 export const zoomFactorRecieverSymbol = Symbol()
 
+/**
+ * Start observing DOM to apply polyfills.
+ *
+ * @param target The parent node to observe. It's useful for observing Marpit
+ *     slides inside shadow DOM. Default is `document`.
+ * @returns A function for stopping and cleaning up observation.
+ */
 export function observe(target: ParentNode = document): () => void {
   if (target[observerSymbol]) return target[observerSymbol]
 
@@ -20,21 +35,70 @@ export function observe(target: ParentNode = document): () => void {
     value: cleanup,
   })
 
-  const observedPolyfills = polyfills()
+  let polyfillsArray: PolyfillsRawArray = []
+  let polyfillsPromiseDone = false
 
-  if (observedPolyfills.length > 0) {
-    const observer = () => {
-      for (const polyfill of observedPolyfills) polyfill({ target })
-      if (enableObserver) window.requestAnimationFrame(observer)
+  ;(async () => {
+    try {
+      polyfillsArray = await polyfills()
+    } finally {
+      polyfillsPromiseDone = true
     }
-    observer()
+  })()
+
+  const observer = () => {
+    for (const polyfill of polyfillsArray) polyfill({ target })
+
+    if (polyfillsPromiseDone && polyfillsArray.length === 0) return
+    if (enableObserver) window.requestAnimationFrame(observer)
   }
+  observer()
 
   return cleanup
 }
 
-export const polyfills = (): Array<(opts: PolyfillOption) => void> =>
-  navigator.vendor === 'Apple Computer, Inc.' ? [webkit] : []
+/**
+ * Returns an array of polyfill functions that must call for the current browser
+ * environment.
+ *
+ * Including polyfills in the returned array are simply determined by the kind of
+ * browser. If you want detailed polyfills that were passed accurate feature
+ * detections, call asyncronous version by `polyfills().then()` or
+ * `await polyfills()`.
+ *
+ * ```js
+ * import { polyfills } from '@marp-team/marpit-svg-polyfill'
+ *
+ * polyfills().then((polyfills) => {
+ *  for (const polyfill of polyfills) polyfill()
+ * })
+ * ```
+ *
+ * @returns A thenable array including polyfill functions
+ */
+export const polyfills = (): PolyfillsArray => {
+  const isSafari = navigator.vendor === 'Apple Computer, Inc.'
+
+  // Sync version of polyfills() has no feature detection. Detect only by the
+  // kind of browser.
+  const polyfillsSync: PolyfillsRawArray = isSafari ? [webkit] : []
+
+  const polyfillsPromiseLike: PromiseLike<PolyfillsRawArray> = {
+    then: ((resolve) => {
+      if (isSafari) {
+        isRequiredPolyfill().then((required) => {
+          resolve?.(required ? [webkit] : [])
+        })
+      } else {
+        resolve?.([])
+      }
+
+      return polyfillsPromiseLike
+    }) as PolyfillsArray['then'],
+  }
+
+  return Object.assign(polyfillsSync, polyfillsPromiseLike)
+}
 
 let previousZoomFactor: number
 let zoomFactorFromParent: number | undefined
@@ -46,7 +110,14 @@ export const _resetCachedZoomFactor = () => {
 
 _resetCachedZoomFactor()
 
-export function webkit(opts?: number | (PolyfillOption & { zoom?: number })) {
+export function webkit(
+  opts?:
+    | number
+    | (PolyfillOption & {
+        /** A zoom factor applied in the current view. You have to specify manually because there is not a reliable way to get the actual zoom factor in the browser. */
+        zoom?: number
+      })
+) {
   const target = (typeof opts === 'object' && opts.target) || document
   const zoom = typeof opts === 'object' ? opts.zoom : opts
 
@@ -56,6 +127,11 @@ export function webkit(opts?: number | (PolyfillOption & { zoom?: number })) {
       value: true,
     })
 
+    // Repaint viewport forcibly when initial observing, to clear buggy SVG debris
+    document.body.style['zoom'] = 1.0001
+    void document.body.offsetHeight
+    document.body.style['zoom'] = 1
+
     window.addEventListener('message', ({ data, origin }) => {
       if (origin !== window.origin) return
 
@@ -79,9 +155,9 @@ export function webkit(opts?: number | (PolyfillOption & { zoom?: number })) {
     (svg) => {
       if (!svg.style.transform) svg.style.transform = 'translateZ(0)'
 
-      // NOTE: Safari reflects a zoom level to SVG's currentScale property, but
-      // the other browsers will always return 1. You have to specify the zoom
-      // factor manually if used in outdated Blink engine. (e.g. Electron)
+      // Safari 16.3 and eariler versions had applied the current scale factor
+      // of the view to `currentScale` property. In others, it becomes `1` as
+      // long as not set the custom scale to SVG element.
       const zoomFactor = zoom || zoomFactorFromParent || svg.currentScale || 1
 
       if (previousZoomFactor !== zoomFactor) {

src/utils/feature-detection.ts

@@ -0,0 +1,27 @@
+let _isRequiredPolyfill: boolean | undefined
+
+export const isRequiredPolyfill = async () => {
+  if (_isRequiredPolyfill === undefined) {
+    const canvas = document.createElement('canvas')
+    canvas.width = 10
+    canvas.height = 10
+
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const ctx = canvas.getContext('2d')!
+
+    const svgImg = new Image(10, 10)
+    const svgOnLoadPromise = new Promise<void>((resolve) => {
+      svgImg.addEventListener('load', () => resolve())
+    })
+
+    svgImg.crossOrigin = 'anonymous'
+    svgImg.src =
+      'data:image/svg+xml;charset=utf8,%3Csvg%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%20width%3D%2210%22%20height%3D%2210%22%20viewBox%3D%220%200%201%201%22%3E%3CforeignObject%20width%3D%221%22%20height%3D%221%22%20requiredExtensions%3D%22http%3A%2F%2Fwww.w3.org%2F1999%2Fxhtml%22%3E%3Cdiv%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1999%2Fxhtml%22%20style%3D%22width%3A%201px%3B%20height%3A%201px%3B%20background%3A%20red%3B%20position%3A%20relative%22%3E%3C%2Fdiv%3E%3C%2FforeignObject%3E%3C%2Fsvg%3E'
+
+    await svgOnLoadPromise
+    ctx.drawImage(svgImg, 0, 0)
+
+    _isRequiredPolyfill = ctx.getImageData(5, 5, 1, 1).data[3] < 128
+  }
+  return _isRequiredPolyfill
+}

test/polyfill.ts

@@ -19,23 +19,40 @@ describe('Marpit SVG polyfill', () => {
     let spy: jest.SpyInstance
 
     beforeEach(() => {
-      spy = jest.spyOn(window, 'requestAnimationFrame')
+      document.body.innerHTML = '<svg data-marpit-svg></svg>'
+      spy = jest.spyOn(window, 'requestAnimationFrame').mockImplementation()
     })
 
-    it('has no operations when running in not supported browser', () => {
+    it('has no operations when running in not supported browser', async () => {
       observe()
-      expect(spy).not.toHaveBeenCalled()
+      expect(spy).toHaveBeenCalledTimes(1)
+
+      // Wait for detecting whether polyfill is required
+      await new Promise((res) => setTimeout(res, 0))
+      spy.mock.calls[0][0]()
+
+      const svg = document.querySelector<SVGElement>('svg[data-marpit-svg]')
+      expect(svg?.style.transform).toBeFalsy()
     })
 
-    it('applies polyfill once when running in WebKit browser', () => {
+    it('applies polyfill once when running in WebKit browser', async () => {
       vendor.mockImplementation(() => 'Apple Computer, Inc.')
 
       observe()
       expect(spy).toHaveBeenCalledTimes(1)
 
-      // Call requestAnimationFrame only once
-      observe()
-      expect(spy).toHaveBeenCalledTimes(1)
+      const observer = spy.mock.calls[0][0]
+
+      // Wait for detecting whether polyfill is required
+      await new Promise((res) => setTimeout(res, 0))
+      observer()
+
+      // And wait canvas rendering for feature detection
+      await new Promise((res) => setTimeout(res, 0))
+      observer()
+
+      const svg = document.querySelector<SVGElement>('svg[data-marpit-svg]')
+      expect(svg?.style.transform).toBeTruthy()
     })
 
     describe('Clean-up function', () => {
@@ -53,19 +70,23 @@ describe('Marpit SVG polyfill', () => {
     })
 
     describe('Different target', () => {
-      it('availables observation for different target', () => {
+      it('availables observation for different target', async () => {
         vendor.mockImplementation(() => 'Apple Computer, Inc.')
 
         const element = document.createElement('div')
         const querySpy = jest.spyOn(element, 'querySelectorAll')
         const cleanup = observe(element)
+        expect(spy).toHaveBeenCalledTimes(1)
+
+        // Wait for detecting whether polyfill is required
+        await new Promise((res) => setTimeout(res, 0))
+        spy.mock.calls[0][0]()
 
         expect(element[observerSymbol]).toStrictEqual(cleanup)
         expect(querySpy).toHaveBeenCalled()
 
         // Returns always same clean-up function even if observing some times
         expect(observe(element)).toStrictEqual(cleanup)
-        expect(spy).toHaveBeenCalledTimes(1)
       })
     })
   })
@@ -84,11 +105,11 @@ describe('Marpit SVG polyfill', () => {
     })
 
     it('applies transform style to SVG element for repainting', () => {
-      const svg = <SVGElement>document.querySelector('svg[data-marpit-svg]')
-      expect(svg.style.transform).not.toContain('translateZ(0)')
+      const svg = document.querySelector<SVGElement>('svg[data-marpit-svg]')
+      expect(svg?.style.transform).not.toContain('translateZ(0)')
 
       webkit()
-      expect(svg.style.transform).toContain('translateZ(0)')
+      expect(svg?.style.transform).toContain('translateZ(0)')
     })
 
     it('applies calculated transform style to section elements for scaling', () => {

tsconfig.json

@@ -7,5 +7,5 @@
     "resolveJsonModule": true,
     "sourceMap": true
   },
-  "include": ["src", "test"]
+  "include": ["src"]
 }