Load MathJax into [[jsxgraph]], fro now loads CDN which is sub optimal for...

Load MathJax into [[jsxgraph]], fro now loads CDN which is sub optimal for closed network users, but this will surely get fixed at soem point.

stack/cas/castext2/blocks/jsxgraph.block.php

@@ -67,6 +67,7 @@ class stack_cas_castext2_jsxgraph extends stack_cas_castext2_block {
         if (isset($xpars['overridejs'])) {
             unset($xpars['overridejs']);
         } 
+
         // Disable scrolling for this.
         $xpars['scrolling'] = false;
         // Set a title.
@@ -91,6 +92,11 @@ class stack_cas_castext2_jsxgraph extends stack_cas_castext2_block {
         $r->items[] = new MP_String(json_encode($xpars));
 
         // Plug in some style and scripts.
+        $mathjax = stack_get_mathjax_url();
+        $r->items[] = new MP_List([
+            new MP_String('script'),
+            new MP_String(json_encode(['type' => 'text/javascript', 'src' => $mathjax]))
+        ]);
         $r->items[] = new MP_List([
             new MP_String('style'),
             new MP_String(json_encode(['href' => $css]))

vle_specific.php

@@ -179,3 +179,11 @@ function stack_cors_link(string $filename): string {
     return (new moodle_url(
             '/question/type/stack/corsscripts/cors.php', ['name' => $filename]))->out(false);
 }
+
+/*
+ * Gets the URL used for MathJax, might be VLE local.
+ */
+function stack_get_mathjax_url(): string {
+    // TODO: figure out how to support VLE local with CORS.
+    return 'https://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML';
+}
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