Update math equation rendering

This commit changes nothing in the RCE, but changes how canvas renders
equations in the resulting page. Rather than
adding mathml in a hidden span adjacent to the equation image for
MathJax to process, this change replaces the image with a span containing
the LaTex source for MathJax to format.  This is better for a couple
reasons.

MathJax is not intended for formatting equations as they are
being edited and dealing with MathJax processed equations in the RCE when you
may want to edit an existing equation is never going to work well.

The visible MathJax-ified equations in the resulting page provides the
accessiblity we require.

This approach will update all existing content with math images,
so old content gets the benefit too.

Contrary to what some believe, you will not be able to select, copy
and paste parts of an equation.

closes: LS-1401
flag=new_math_equation_handling

test plan:
  - with new_math_equation_handling flag on
  - insert a math equation in the RCE
  > notice that when you click on the equation's image, you do not
    get the "Image Options" popup button
  - click on the equation
  > expect the "Edit Equation" popup button, not "Image Options"
  - edit the equation and save
  > expect it to be updated
  - save the page
  > expect the equation to fade into view after being processed by MathJax.
  > expect the MathJax menu when you right click in it
  > expect screenreaders read it nicely
  - edit the page again
  > expect the equation as an image again.
  > expect to be able to edit the equation
  - switch your user to a different language
  - open a page with an equation and right-click in the eq.
  > expect the mathjax context menu to be in the user's language
    (assuming mathjax supports it)

Change-Id: Ieac6785d51c0cab475b1176712f46fc2c964ff71
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/247471
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Jackson Howe <jackson.howe@instructure.com>
QA-Review: Daniel Sasaki <dsasaki@instructure.com>
Product-Review: Peyton Craighill <pcraighill@instructure.com>

app/controllers/application_controller.rb

@@ -214,7 +214,7 @@ class ApplicationController < ActionController::Base
 
   # put feature checks on Account.site_admin and @domain_root_account that we're loading for every page in here
   # so altogether we can get them faster the vast majority of the time
-  JS_ENV_SITE_ADMIN_FEATURES = [:cc_in_rce_video_tray, :featured_help_links, :rce_lti_favorites].freeze
+  JS_ENV_SITE_ADMIN_FEATURES = [:cc_in_rce_video_tray, :featured_help_links, :rce_lti_favorites, :new_math_equation_handling].freeze
   JS_ENV_ROOT_ACCOUNT_FEATURES = [
     :direct_share, :assignment_bulk_edit, :responsive_awareness, :recent_history,
     :responsive_misc, :product_tours, :module_dnd, :files_dnd, :unpublished_courses, :bulk_delete_pages
@@ -2138,7 +2138,7 @@ class ApplicationController < ActionController::Base
         is_public: is_public
       ).processed_url
     end
-    UserContent.escape(rewriter.translate_content(str), request.host_with_port)
+    UserContent.escape(rewriter.translate_content(str), request.host_with_port, Account.site_admin.feature_enabled?(:new_math_equation_handling))
   end
   helper_method :public_user_content
 

app/stylesheets/base/_ic_utilities.scss

@@ -80,28 +80,63 @@
   visibility: hidden;
 }
 
+.math_equation_latex {
+  visibility: hidden;
+  display: inline-block;
+}
+.fade-in-equation {
+  visibility: visible;
+  animation: fadein ease 0.3s;
+}
+@keyframes fadein {
+  from {
+    opacity: 0;
+  }
+  to {
+    opacity: 1;
+  }
+}
+
 // Visibility utilities
 
 // For desktops
-.hidden-phone      { }
-.hidden-tablet     { }
-.hidden-desktop    { display: none !important; }
-.visible-desktop   { display: inherit !important; }
+.hidden-phone {
+}
+.hidden-tablet {
+}
+.hidden-desktop {
+  display: none !important;
+}
+.visible-desktop {
+  display: inherit !important;
+}
 
 // Tablets & small desktops only
 @media (min-width: 768px) and (max-width: 979px) {
   // Hide everything else
-  .hidden-desktop    { display: inherit !important; }
-  .visible-desktop   { display: none !important ; }
+  .hidden-desktop {
+    display: inherit !important;
+  }
+  .visible-desktop {
+    display: none !important ;
+  }
   // Hide
-  .hidden-tablet     { display: none !important; }
+  .hidden-tablet {
+    display: none !important;
+  }
 }
 
 // Phones only
 @media (max-width: 767px) {
   // Hide everything else
-  .hidden-desktop    { display: inherit !important; }
-  .visible-desktop   { display: none !important; }
+  .hidden-desktop {
+    display: inherit !important;
+  }
+  .visible-desktop {
+    display: none !important;
+  }
   // Hide
-  .hidden-phone      { display: none !important; }
+  .hidden-phone {
+    display: none !important;
+  }
 }

config/feature_flags/learning_activities_release_flags.yml

@@ -56,3 +56,11 @@ enable_fullstory:
   description: |-
     Include FullStory recording of the user's session
   applies_to: SiteAdmin
+new_math_equation_handling:
+  state: hidden
+  display_name: Updated math equation display
+  description: |-
+    Replaces the existing image of the math equation plus the hidden mathml
+    with a MathJax formatted version. This provides better accessibility
+    and many options for the reader to interact with the equation on the page.
+  applies_to: SiteAdmin

lib/user_content.rb

@@ -20,7 +20,7 @@ require 'ritex'
 require 'securerandom'
 
 module UserContent
-  def self.escape(str, current_host = nil)
+  def self.escape(str, current_host = nil, use_updated_math_rendering = false)
     html = Nokogiri::HTML::DocumentFragment.parse(str)
     find_user_content(html) do |obj, uc|
       uuid = SecureRandom.uuid
@@ -55,13 +55,23 @@ module UserContent
 
     find_equation_images(html) do |node|
       equation = node['data-equation-content'] || node['alt']
-      mathml = UserContent.latex_to_mathml(equation)
-      next if mathml.blank?
+      next if equation.blank?
+      if use_updated_math_rendering
+        # replace the equation image with a span containing the
+        # LaTex, which MathJAX will typeset once we're in the browser
+        latex_span = Nokogiri::HTML::DocumentFragment.parse(
+          "<span class=\"math_equation_latex\">\\(#{equation}\\)</span>"
+        )
+        node.replace(latex_span)
+      else
+        mathml = UserContent.latex_to_mathml(equation)
+        next if mathml.blank?
         
-      mathml_span = Nokogiri::HTML::DocumentFragment.parse(
-        "<span class=\"hidden-readable\">#{mathml}</span>"
-      )
-      node.add_next_sibling(mathml_span)
+        mathml_span = Nokogiri::HTML::DocumentFragment.parse(
+          "<span class=\"hidden-readable\">#{mathml}</span>"
+        )
+        node.add_next_sibling(mathml_span)
+      end
     end
 
     html.to_s.html_safe

packages/canvas-rce/src/rce/plugins/instructure_equation/plugin.js

@@ -53,6 +53,25 @@ tinymce.create('tinymce.plugins.InstructureEquation', {
         return () => ed.off('NodeChange', toggleActive)
       }
     })
+
+    function isEquationImage(node) {
+      return node.tagName === 'IMG' && node.classList.contains('equation_image')
+    }
+
+    ed.ui.registry.addButton('instructure-equation-options', {
+      onAction(/* buttonApi */) {
+        ed.execCommand('instructureEquation')
+      },
+
+      text: formatMessage('Edit Equation')
+    })
+
+    ed.ui.registry.addContextToolbar('instructure-equation-toolbar', {
+      items: 'instructure-equation-options',
+      position: 'node',
+      predicate: isEquationImage,
+      scope: 'node'
+    })
   }
 })
 

packages/canvas-rce/src/rce/plugins/instructure_image/plugin.js

@@ -120,6 +120,10 @@ tinymce.create('tinymce.plugins.InstructureImagePlugin', {
      * Register the Image "Options" button that will open the Image Options
      * tray.
      */
+
+    function canUpdateImageProps(node) {
+      return !node.classList.contains('equation_image') && isImageEmbed(node)
+    }
     const buttonAriaLabel = formatMessage('Show image options')
     editor.ui.registry.addButton('instructure-image-options', {
       onAction(/* buttonApi */) {
@@ -134,7 +138,7 @@ tinymce.create('tinymce.plugins.InstructureImagePlugin', {
     editor.ui.registry.addContextToolbar('instructure-image-toolbar', {
       items: 'instructure-image-options',
       position: 'node',
-      predicate: isImageEmbed,
+      predicate: canUpdateImageProps,
       scope: 'node'
     })
   },

public/javascripts/mathml.js

@@ -25,24 +25,37 @@ const localConfig = {
   }
 }
 
-export function loadMathJax(configFile, cb = null) {
+export function loadMathJax(configFile = 'TeX-MML-AM_HTMLorMML', cb = null) {
   if (!isMathJaxLoaded()) {
+    const locale = ENV.locale || 'en'
     // signal local config to mathjax as it loads
     window.MathJax = localConfig
     $.getScript(
-      `//cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.5/MathJax.js?config=${configFile}`,
-      cb
+      `//cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.5/MathJax.js?config=${configFile}&locale=${locale}`,
+      () => {
+        window.MathJax.Hub.Register.MessageHook('End Math', function(message) {
+          message[1]
+            .querySelectorAll('.math_equation_latex')
+            .forEach(m => m.classList.add('fade-in-equation'))
+        })
+
+        cb?.()
+      }
     )
-  } else if (typeof cb === 'function') {
+  } else {
     // Make sure we always call the callback if it is loaded already and make sure we
     // also reprocess the page since chances are if we are requesting MathJax again,
     // something has changed on the page and needs to get pulled into the MathJax ecosystem
     window.MathJax.Hub.Reprocess()
-    cb()
+    cb?.()
   }
 }
 
 export function isMathMLOnPage() {
+  // handle the change from image + hidden mathml to mathjax formatted latex
+  if (document.querySelector('.math_equation_latex')) {
+    return true
+  }
   const mathElements = document.getElementsByTagName('math')
   for (let i = 0; i < mathElements.length; i++) {
     const $el = $(mathElements[i])
@@ -51,14 +64,14 @@ export function isMathMLOnPage() {
 }
 
 export function isMathJaxLoaded() {
-  return !(typeof MathJax === 'undefined')
+  return !!window.MathJax?.Hub
 }
 
 /*
  * elem: string with elementId or en elem object
  */
 export function reloadElement(elem) {
-  if (window.MathJax) {
+  if (isMathJaxLoaded()) {
     window.MathJax.Hub.Queue(['Typeset', window.MathJax.Hub, elem])
   }
 }

spec/javascripts/jsx/mathmlSpec.js

@@ -24,6 +24,7 @@ QUnit.module('MathML and MathJax test', {
     const mathElem = document.createElement('math')
     mathElem.innerHTML = '<mi>&#x3C0;</mi> <msup> <mi>r</mi> <mn>2</mn> </msup>'
     $('body')[0].appendChild(mathElem)
+    window.ENV.locale = 'en'
   }
 })
 
@@ -37,7 +38,11 @@ test('loadMathJax loads mathJax', () => {
 
 test('loadMathJax does not load mathJax', () => {
   sinon.stub($, 'getScript')
-  window.MathJax = {}
+  window.MathJax = {
+    Hub: {
+      Reprocess: () => {}
+    }
+  }
   mathml.loadMathJax('bogus')
   ok(!$.getScript.called)
   $.getScript.restore()
@@ -48,7 +53,7 @@ test('isMathMLOnPage returns true', () => {
 })
 
 test('isMathJaxLoaded return true', () => {
-  window.MathJax = {}
+  window.MathJax = {Hub: {}}
   ok(mathml.isMathJaxLoaded())
 })