[markdown-preview] Optimize re-rendering of content in a preview pane…

packages/markdown-preview/lib/main.js

@@ -12,10 +12,18 @@ const isMarkdownPreviewView = function (object) {
 }
 
 module.exports = {
-  activate () {
+  activate() {
     this.disposables = new CompositeDisposable()
     this.commandSubscriptions = new CompositeDisposable()
 
+    this.style = new CSSStyleSheet()
+
+    // When we upgrade Electron, we can push onto `adoptedStyleSheets`
+    // directly. For now, we have to do this silly thing.
+    let styleSheets = Array.from(document.adoptedStyleSheets ?? [])
+    styleSheets.push(this.style)
+    document.adoptedStyleSheets = styleSheets
+
     this.disposables.add(
       atom.config.observe('markdown-preview.grammars', grammars => {
         this.commandSubscriptions.dispose()
@@ -53,6 +61,22 @@ module.exports = {
       })
     )
 
+    this.disposables.add(
+      atom.config.observe('editor.fontFamily', (fontFamily) => {
+        // Keep the user's `fontFamily` setting in sync with preview styles.
+        // `pre` blocks will use this font automatically, but `code` elements
+        // need a specific style rule.
+        //
+        // Since this applies to all content, we should declare this only once,
+        // instead of once per preview view.
+        this.style.replaceSync(`
+          .markdown-preview code {
+            font-family: ${fontFamily} !important;
+          }
+        `)
+      })
+    )
+
     const previewFile = this.previewFile.bind(this)
     for (const extension of [
       'markdown',
@@ -94,12 +118,12 @@ module.exports = {
     )
   },
 
-  deactivate () {
+  deactivate() {
     this.disposables.dispose()
     this.commandSubscriptions.dispose()
   },
 
-  createMarkdownPreviewView (state) {
+  createMarkdownPreviewView(state) {
     if (state.editorId || fs.isFileSync(state.filePath)) {
       if (MarkdownPreviewView == null) {
         MarkdownPreviewView = require('./markdown-preview-view')
@@ -108,7 +132,7 @@ module.exports = {
     }
   },
 
-  toggle () {
+  toggle() {
     if (isMarkdownPreviewView(atom.workspace.getActivePaneItem())) {
       atom.workspace.destroyActivePaneItem()
       return
@@ -129,11 +153,11 @@ module.exports = {
     }
   },
 
-  uriForEditor (editor) {
+  uriForEditor(editor) {
     return `markdown-preview://editor/${editor.id}`
   },
 
-  removePreviewForEditor (editor) {
+  removePreviewForEditor(editor) {
     const uri = this.uriForEditor(editor)
     const previewPane = atom.workspace.paneForURI(uri)
     if (previewPane != null) {
@@ -144,7 +168,7 @@ module.exports = {
     }
   },
 
-  addPreviewForEditor (editor) {
+  addPreviewForEditor(editor) {
     const uri = this.uriForEditor(editor)
     const previousActivePane = atom.workspace.getActivePane()
     const options = { searchAllPanes: true }
@@ -161,7 +185,7 @@ module.exports = {
       })
   },
 
-  previewFile ({ target }) {
+  previewFile({ target }) {
     const filePath = target.dataset.path
     if (!filePath) {
       return
@@ -178,7 +202,7 @@ module.exports = {
     })
   },
 
-  async copyHTML () {
+  async copyHTML() {
     const editor = atom.workspace.getActiveTextEditor()
     if (editor == null) {
       return
@@ -191,13 +215,14 @@ module.exports = {
     const html = await renderer.toHTML(
       text,
       editor.getPath(),
-      editor.getGrammar()
+      editor.getGrammar(),
+      editor.id
     )
 
     atom.clipboard.write(html)
   },
 
-  saveAsHTML () {
+  saveAsHTML() {
     const activePaneItem = atom.workspace.getActivePaneItem()
     if (isMarkdownPreviewView(activePaneItem)) {
       atom.workspace.getActivePane().saveItemAs(activePaneItem)

packages/markdown-preview/lib/markdown-preview-view.js

@@ -1,4 +1,5 @@
 const path = require('path')
+const morphdom = require('morphdom')
 
 const { Emitter, Disposable, CompositeDisposable, File } = require('atom')
 const _ = require('underscore-plus')
@@ -17,6 +18,7 @@ module.exports = class MarkdownPreviewView {
     this.element = document.createElement('div')
     this.element.classList.add('markdown-preview')
     this.element.tabIndex = -1
+
     this.emitter = new Emitter()
     this.loaded = false
     this.disposables = new CompositeDisposable()
@@ -32,6 +34,7 @@ module.exports = class MarkdownPreviewView {
         })
       )
     }
+    this.editorCache = new renderer.EditorCache(editorId)
   }
 
   serialize() {
@@ -52,6 +55,7 @@ module.exports = class MarkdownPreviewView {
   destroy() {
     this.disposables.dispose()
     this.element.remove()
+    this.editorCache.destroy()
   }
 
   registerScrollCommands() {
@@ -83,7 +87,7 @@ module.exports = class MarkdownPreviewView {
     return this.emitter.on('did-change-title', callback)
   }
 
-  onDidChangeModified(callback) {
+  onDidChangeModified(_callback) {
     // No op to suppress deprecation warning
     return new Disposable()
   }
@@ -270,7 +274,22 @@ module.exports = class MarkdownPreviewView {
     return this.getMarkdownSource()
       .then(source => {
         if (source != null) {
-          return this.renderMarkdownText(source)
+          if (this.loaded) {
+            return this.renderMarkdownText(source);
+          } else {
+            // If we haven't loaded yet, defer before we render the Markdown
+            // for the first time. This allows the pane to appear and to
+            // display the loading indicator. Otherwise the first render
+            // happens before the pane is even visible.
+            //
+            // This doesn't slow anything down; it just shifts the work around
+            // so that the pane appears earlier in the cycle.
+            return new Promise((resolve) => {
+              setTimeout(() => {
+                resolve(this.renderMarkdownText(source))
+              }, 0)
+            })
+          }
         }
       })
       .catch(reason => this.showError({ message: reason }))
@@ -309,18 +328,34 @@ module.exports = class MarkdownPreviewView {
 
   async renderMarkdownText(text) {
     const { scrollTop } = this.element
-
     try {
-      const domFragment = await renderer.toDOMFragment(
+      const [domFragment, done] = await renderer.toDOMFragment(
         text,
         this.getPath(),
-        this.getGrammar()
+        this.getGrammar(),
+        this.editorId
       )
 
       this.loading = false
       this.loaded = true
-      this.element.textContent = ''
-      this.element.appendChild(domFragment)
+
+      // Clone the existing container
+      let newElement = this.element.cloneNode(false)
+      newElement.appendChild(domFragment)
+
+      morphdom(this.element, newElement, {
+        onBeforeNodeDiscarded(node) {
+          // Don't discard `atom-text-editor` elements despite the fact that
+          // they don't exist in the new content.
+          if (node.nodeName === 'ATOM-TEXT-EDITOR') {
+            return false
+          }
+        }
+      })
+
+      await done(this.element)
+      this.element.classList.remove('loading')
+
       this.emitter.emit('did-change-markdown')
       this.element.scrollTop = scrollTop
     } catch (error) {
@@ -400,7 +435,7 @@ module.exports = class MarkdownPreviewView {
       .join('\n')
       .replace(/atom-text-editor/g, 'pre.editor-colors')
       .replace(/:host/g, '.host') // Remove shadow-dom :host selector causing problem on FF
-      .replace(cssUrlRegExp, function (match, assetsName, offset, string) {
+      .replace(cssUrlRegExp, function (_match, assetsName, _offset, _string) {
         // base64 encode assets
         const assetPath = path.join(__dirname, '../assets', assetsName)
         const originalData = fs.readFileSync(assetPath, 'binary')
@@ -413,6 +448,7 @@ module.exports = class MarkdownPreviewView {
 
   showError(result) {
     this.element.textContent = ''
+    this.element.classList.remove('loading')
     const h2 = document.createElement('h2')
     h2.textContent = 'Previewing Markdown Failed'
     this.element.appendChild(h2)
@@ -425,11 +461,7 @@ module.exports = class MarkdownPreviewView {
 
   showLoading() {
     this.loading = true
-    this.element.textContent = ''
-    const div = document.createElement('div')
-    div.classList.add('markdown-spinner')
-    div.textContent = 'Loading Markdown\u2026'
-    this.element.appendChild(div)
+    this.element.classList.add('loading')
   }
 
   selectAll() {