Some updates to the help popup

This makes a few changes to the help popup:

- Move css to chrome.css, since this is a UI element.
- Move HTML code to index.hbs instead of generated in JavaScript.
  In general I prefer to keep HTML out of JavaScript when possible,
  and I didn't see a particular reason to avoid it.
- Added a click handler to dismiss the popup.
- Make sure handlers get removed when dismissed.
- Use `mdbook-` prefixes for IDs to avoid collisions with headers.
- Don't show search if it isn't enabled.
- Add the new `/` shortcut.
- Use flex layout for better positioning.
- Dim out the surrounding text using an overlay.
- Various other styling tweaks.
- Add a GUI test.

Author: ehuss

src/front-end/css/chrome.css

@@ -656,3 +656,46 @@ html:not(.sidebar-resizing) .sidebar {
     margin-inline-start: -14px;
     width: 14px;
 }
+
+/* The container for the help popup that covers the whole window. */
+#mdbook-help-container {
+    /* Position and size for the whole window. */
+    position: fixed;
+    top: 0;
+    left: 0;
+    right: 0;
+    bottom: 0;
+    /* This uses flex layout (which is set in book.js), and centers the popup
+       in the window.*/
+    display: none;
+    align-items: center;
+    justify-content: center;
+    z-index: 1000;
+    /* Dim out the book while the popup is visible. */
+    background: var(--overlay-bg);
+}
+
+/* The popup help box. */
+#mdbook-help-popup {
+    box-shadow: 0 4px 24px rgba(0,0,0,0.15);
+    min-width: 300px;
+    max-width: 500px;
+    width: 100%;
+    box-sizing: border-box;
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    background-color: var(--bg);
+    color: var(--fg);
+    border-width: 1px;
+    border-color: var(--theme-popup-border);
+    border-style: solid;
+    border-radius: 8px;
+    padding: 10px;
+}
+
+.mdbook-help-title {
+    text-align: center;
+    /* mdbook's margin for h2 is way too large. */
+    margin: 10px;
+}

src/front-end/css/general.css

@@ -277,33 +277,3 @@ sup {
 .result-no-output {
     font-style: italic;
 }
-
-#help-overlay {
-    position: fixed;
-    display: none;
-    width: 20%;
-    height: 60%;
-    top: 10%;
-    left: 40%;
-    right: 0;
-    bottom: 0;
-    background-color: rgba(225,225,225,1);
-    color: black;
-    z-index: 2;
-    cursor: pointer;
-    border-width: 3px;
-    border-color: black;
-    border-style: solid;
-    border-radius: 25px;
-
-    padding: 10px;
-}
-#help-overlay kbd {
-    border-width: 1px;
-    border-color: black;
-    border-style: solid;
-    background-color: white;
-}
-#help-title {
-    text-align: center;
-}

src/front-end/css/variables.css

@@ -64,6 +64,8 @@
     --copy-button-filter-hover: invert(68%) sepia(55%) saturate(531%) hue-rotate(341deg) brightness(104%) contrast(101%);
 
     --footnote-highlight: #2668a6;
+
+    --overlay-bg: rgba(33, 40, 48, 0.4);
 }
 
 .coal {
@@ -115,6 +117,8 @@
     --copy-button-filter-hover: invert(36%) sepia(70%) saturate(503%) hue-rotate(167deg) brightness(98%) contrast(89%);
 
     --footnote-highlight: #4079ae;
+
+    --overlay-bg: rgba(33, 40, 48, 0.4);
 }
 
 .light, html:not(.js) {
@@ -166,6 +170,8 @@
     --copy-button-filter-hover: invert(14%) sepia(93%) saturate(4250%) hue-rotate(243deg) brightness(99%) contrast(130%);
 
     --footnote-highlight: #7e7eff;
+
+    --overlay-bg: rgba(200, 200, 205, 0.4);
 }
 
 .navy {
@@ -217,6 +223,8 @@
     --copy-button-filter-hover: invert(46%) sepia(20%) saturate(1537%) hue-rotate(156deg) brightness(85%) contrast(90%);
 
     --footnote-highlight: #4079ae;
+
+    --overlay-bg: rgba(33, 40, 48, 0.4);
 }
 
 .rust {
@@ -266,6 +274,8 @@
     --copy-button-filter-hover: invert(77%) sepia(16%) saturate(1798%) hue-rotate(328deg) brightness(98%) contrast(83%);
 
     --footnote-highlight: #d3a17a;
+
+    --overlay-bg: rgba(150, 150, 150, 0.25);
 }
 
 @media (prefers-color-scheme: dark) {

src/front-end/js/book.js

@@ -644,30 +644,39 @@ aria-label="Show hidden lines"></button>';
             }
         }
         function showHelp() {
-            document.getElementById('help-overlay').style.display = 'block';
-            let help = '<h2 id="help-title">Keyboard shortcuts</h2>';
-            help += '<p>Press <kbd>←</kbd> or <kbd>→</kbd> to navigate between chapters</p>';
-            help += '<p>Press <kbd>s</kbd> to search in the book</p>';
-            help += '<p>Press <kbd>?</kbd> to show this help</p>';
-            help += '<p>Press <kbd>Esc</kbd> to hide this help</p>';
+            const container = document.getElementById('mdbook-help-container');
+            const overlay = document.getElementById('mdbook-help-popup');
+            container.style.display = 'flex';
 
-            document.getElementById('help-overlay').innerHTML = help;
-
-            document.addEventListener('keydown', function(e) {
-                if (e.altKey || e.ctrlKey || e.metaKey || e.shiftKey) {
+            // Clicking outside the popup will dismiss it.
+            const mouseHandler = event => {
+                if (overlay.contains(event.target)) {
                     return;
                 }
-
-                switch (e.key) {
-                case 'Escape':
-                    e.preventDefault();
+                if (event.button !== 0) {
+                    return;
+                }
+                event.preventDefault();
+                event.stopPropagation();
+                document.removeEventListener('mousedown', mouseHandler);
+                hideHelp();
+            };
+
+            // Pressing esc will dismiss the popup.
+            const escapeKeyHandler = event => {
+                if (event.key === 'Escape') {
+                    event.preventDefault();
+                    event.stopPropagation();
+                    document.removeEventListener('keydown', escapeKeyHandler, true);
                     hideHelp();
-                    break;
                 }
-            });
+            };
+            document.addEventListener('keydown', escapeKeyHandler, true);
+            document.getElementById('mdbook-help-container')
+                .addEventListener('mousedown', mouseHandler);
         }
         function hideHelp() {
-            document.getElementById('help-overlay').style.display = 'none';
+            document.getElementById('mdbook-help-container').style.display = 'none';
         }
 
         // Usually needs the Shift key to be pressed

src/front-end/templates/index.hbs

@@ -63,7 +63,19 @@
         <script src="{{ resource "toc.js" }}"></script>
     </head>
     <body>
-    <div id="help-overlay"></div>
+    <div id="mdbook-help-container">
+        <div id="mdbook-help-popup">
+            <h2 class="mdbook-help-title">Keyboard shortcuts</h2>
+            <div>
+                <p>Press <kbd>←</kbd> or <kbd>→</kbd> to navigate between chapters</p>
+                {{#if search_enabled}}
+                <p>Press <kbd>S</kbd> or <kbd>/</kbd> to search in the book</p>
+                {{/if}}
+                <p>Press <kbd>?</kbd> to show this help</p>
+                <p>Press <kbd>Esc</kbd> to hide this help</p>
+            </div>
+        </div>
+    </div>
     <div id="body-container">
         <!-- Work around some values being stored in localStorage wrapped in quotes -->
         <script>

src/renderer/html_handlebars/hbs_renderer.rs

@@ -667,7 +667,7 @@ fn build_header_links(html: &str) -> String {
     static BUILD_HEADER_LINKS: LazyLock<Regex> = LazyLock::new(|| {
         Regex::new(r#"<h(\d)(?: id="([^"]+)")?(?: class="([^"]+)")?>(.*?)</h\d>"#).unwrap()
     });
-    static IGNORE_CLASS: &[&str] = &["menu-title"];
+    static IGNORE_CLASS: &[&str] = &["menu-title", "mdbook-help-title"];
 
     let mut id_counter = HashMap::new();