Add zoomable images feature

crates/mdbook-html/front-end/css/general.css

@@ -409,3 +409,56 @@ dd > p {
     /* Add some space between the icon and the text. */
     margin-right: 8px;
 }
+
+/* All this code is to handle the "zoomable" images feature. */
+
+/* This one makes the checkbox invisible while keeping it selectable with the keyboard (with the
+   "tab" key). */
+.content .checkbox-img {
+    position: absolute;
+    width: 1px;
+    height: 1px;
+    padding: 0;
+    margin: -1px;
+    overflow: hidden;
+    clip: rect(0, 0, 0, 0);
+    white-space: nowrap;
+    border: 0;
+}
+/* When the input is focused, we make it appear to the user by adding an outline to the img
+   instead */
+.content .checkbox-img:focus + img {
+    outline: auto;
+}
+/* The "zoomed-in" image is not displayed until the checkbox is "ticked". */
+.content .checkbox-img:not(:checked) ~ .img-wrapper {
+    display: none;
+}
+.content .checkbox-label {
+    display: block;
+    max-width: 100%;
+}
+.content .checkbox-label img {
+    cursor: zoom-in;
+}
+.content .checkbox-img:checked ~ .img-wrapper {
+    position: fixed;
+    top: 0;
+    left: 0;
+    width: 100vw;
+    height: 100vh;
+    background-color: rgba(0, 0, 0, 0.4);
+    z-index: 1001;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    cursor: zoom-out;
+}
+.content .checkbox-img:checked ~ .img-wrapper > img {
+    --img-padding: 5px;
+    padding: var(--img-padding);
+    background: #999;
+    cursor: zoom-out;
+    max-width: calc(100% - (var(--img-padding) * 2));
+    max-height: calc(100% - (var(--img-padding) * 2));
+}

crates/mdbook-html/front-end/js/book.js

@@ -27,6 +27,10 @@ function mdbook_something_else_has_focus(e) {
     // Check composedPath in case the event happened from something generated
     // from the shadowDOM.
     const target = e.composedPath()[0] || e.target;
+    // If this is the `checkbox-img` input which has the focus, we want to handle it here.
+    if (target.classList.contains('checkbox-img')) {
+        return false;
+    }
     return /^(?:input|select|textarea)$/i.test(target.nodeName);
 }
 
@@ -658,6 +662,12 @@ aria-label="Show hidden lines"></button>';
 })();
 
 (function chapterNavigation() {
+    function zoomOutImages() {
+        for (const elem of Array.from(document.querySelectorAll('input.checkbox-img'))) {
+            elem.checked = false;
+        }
+    }
+
     document.addEventListener('keydown', function(e) {
         if (e.altKey ||
             e.ctrlKey ||
@@ -724,6 +734,9 @@ aria-label="Show hidden lines"></button>';
             e.preventDefault();
             showHelp();
             break;
+        case 'Escape':
+            zoomOutImages();
+            break;
         }
 
         // Rest of the keys are only active when the Shift key is not pressed

crates/mdbook-html/src/html/tree.rs

@@ -9,7 +9,7 @@ use super::tokenizer::parse_html;
 use super::{HtmlRenderOptions, hide_lines, wrap_rust_main};
 use crate::utils::{id_from_content, unique_id};
 use ego_tree::{NodeId, NodeRef, Tree};
-use html5ever::tendril::StrTendril;
+use html5ever::tendril::{SliceExt, StrTendril};
 use html5ever::tokenizer::{TagKind, Token};
 use html5ever::{LocalName, QualName};
 use indexmap::IndexMap;
@@ -69,7 +69,7 @@ impl Node {
 }
 
 /// An HTML element.
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub(crate) struct Element {
     /// The tag name.
     pub(crate) name: QualName,
@@ -565,8 +565,42 @@ where
                 }
                 // This will eat TagEnd::Image
                 let alt = self.text_for_img_alt();
-                img.insert_attr("alt", alt.into());
-                self.append(Node::Element(img));
+                img.insert_attr("alt", alt.to_tendril());
+
+                // If the image is not being rendered inside a link, we can enable the "zoom-in"
+                // feature.
+                if !self
+                    .tag_stack
+                    .iter()
+                    .filter_map(|node_id| {
+                        self.tree
+                            .get(*node_id)
+                            .and_then(|el| el.value().as_element())
+                    })
+                    .any(|el| *el.name.local == *"a")
+                {
+                    let mut label = Element::new("label");
+                    label.insert_attr("class", "checkbox-label".to_tendril());
+                    self.push(Node::Element(label));
+
+                    let mut input = Element::new("input");
+                    input.insert_attr("class", "checkbox-img".to_tendril());
+                    input.insert_attr("type", "checkbox".to_tendril());
+                    self.append(Node::Element(input));
+
+                    self.append(Node::Element(img.clone()));
+
+                    let mut wrapper = Element::new("span");
+                    wrapper.insert_attr("class", "img-wrapper".to_tendril());
+                    self.push_no_stack(Node::Element(wrapper));
+
+                    self.append(Node::Element(img));
+
+                    // We exit the `label` and the `span` (which used push_no_stack).
+                    self.pop();
+                } else {
+                    self.append(Node::Element(img));
+                }
                 return;
             }
             Tag::MetadataBlock(_) => {

guide/src/format/markdown.md

@@ -318,3 +318,7 @@ This feature is enabled by default.
 To disable it, see the [`output.html.admonitions`] config option.
 
 [`output.html.admonitions`]: configuration/renderers.md#html-renderer-options
+
+## Zoom-in
+
+All images in the chapters content have a "zoom-in" feature: you can click on it to make it bigger, and click it again to zoom out. You can focus the image with the keyboard as well, and press the spacebar to zoom in and out as well.

tests/gui/books/basic/src/chapter_1.md

@@ -1,3 +1,9 @@
 # Chapter 1
 
 Side by side [![the logo](rust-logo.svg)](link) [![the logo](rust-logo.svg)](link).
+
+Some text [blob](a).
+
+![rust logo](rust-logo.svg)
+
+[![the logo](rust-logo.svg)](https://rust-lang.org/)

tests/gui/image-zoom.goml

@@ -0,0 +1,87 @@
+// This test ensures that the image zoom-in/zoom-out works as expected.
+
+define-function: (
+    "check-image-not-zoomed-in",
+    [],
+    block {
+        // The "zoomed in" image should not be displayed.
+        assert-css: (".checkbox-label > .img-wrapper", {"display": "none"})
+        // The cursor for the image should be "zoom-in".
+        assert-css: (".checkbox-label > img", {"cursor": "zoom-in"})
+    },
+)
+
+define-function: (
+    "check-image-zoomed-in",
+    [],
+    block {
+        // The image wrapper should now be displayed and have a "zoom-out" cursor.
+        assert-css: (".checkbox-label > .img-wrapper", {"display": "flex", "cursor": "zoom-out"})
+        // Same for the image it contains.
+        assert-css: (
+            ".checkbox-label > .img-wrapper img",
+            {"display": "block", "cursor": "zoom-out"},
+        )
+    },
+)
+
+go-to: |DOC_PATH| + "basic/index.html"
+show-text: true
+call-function: ("check-image-not-zoomed-in", {})
+
+// We click on the image to "zoom in".
+click: ".checkbox-label > img"
+call-function: ("check-image-zoomed-in", {})
+
+// We click on the wrapper to "zoom out".
+click: ".checkbox-label > img"
+// We check that everything is back to the previous state.
+call-function: ("check-image-not-zoomed-in", {})
+
+// We test that the "escape" key also hides the "zoomed in" image.
+// We click on the image to "zoom in".
+click: ".checkbox-label > img"
+call-function: ("check-image-zoomed-in", {})
+press-key: "Escape"
+// We check that everything is back to the previous state.
+call-function: ("check-image-not-zoomed-in", {})
+
+// We test that we can zoom in and out using only the keyboard.
+// First we focus on the link just before the image we want to zoom in.
+focus: "a[href='a']"
+assert: "a[href='a']:focus"
+press-key: "Tab"
+// We check that the checkbox to "zoom in" is focused.
+assert: ".checkbox-img:focus"
+// We check that the image about to be zoomed in has the outline.
+store-css: (".checkbox-img:focus", {"outline": outline})
+// Because we're using "auto" to match the system outline, we cannot check the whole value directly
+// so instead we check if "auto" is present.
+assert-variable: (outline, "auto", CONTAINS)
+// We zoom in.
+press-key: "Space"
+call-function: ("check-image-zoomed-in", {})
+// We press the key again to zoom out.
+press-key: "Space"
+call-function: ("check-image-not-zoomed-in", {})
+// We now check it works with the "Escape" key as well.
+press-key: "Space"
+call-function: ("check-image-zoomed-in", {})
+press-key: "Escape"
+call-function: ("check-image-not-zoomed-in", {})
+
+// Now we check that images in links (in `<a>` elements) don't get the "zoom-in" feature enabled.
+// There is only one zoomable image.
+assert-count: ("main .checkbox-img", 1)
+// We should have 5 images: 4 "normal" ones visible in the rendered book and one hidden which is
+// used only for the "zoom-in" feature.
+assert-count: ("main img", 5)
+// We check exact paths to ensure the 5 `<img>` are different.
+assert: ("main > p > label.checkbox-label > img:nth-of-type(1)")
+assert: ("main > p > label.checkbox-label > span.img-wrapper > img")
+assert: ("main > p:nth-of-type(1) > a:nth-of-type(1) > img")
+assert: ("main > p:nth-of-type(1) > a:nth-of-type(2) > img")
+assert: ("main > p:not(:nth-of-type(2)) > a > img")
+
+// The cursor for the image in link should not have "zoom-in".
+assert-css: ("main > p > a > img", {"cursor": "pointer"})

tests/testsuite/markdown/basic_markdown/expected/images.html

@@ -1,3 +1,3 @@
 <h1 id="images"><a class="header" href="#images">Images</a></h1>
-<p><img src="https://rust-lang.org/logos/rust-logo-256x256.png" alt="Image “alt” &amp; &quot; &quot;text&quot; &amp; &lt;stuff&gt; url &lt;em&gt;html&lt;/em&gt; — hard break "></p>
-<p><img src="https://rust-lang.org/logos/rust-logo-256x256.png" title="Some title" alt="Image with title"></p>
+<p><label class="checkbox-label"><input class="checkbox-img" type="checkbox"><img src="https://rust-lang.org/logos/rust-logo-256x256.png" alt="Image “alt” &amp; &quot; &quot;text&quot; &amp; &lt;stuff&gt; url &lt;em&gt;html&lt;/em&gt; — hard break "><span class="img-wrapper"><img src="https://rust-lang.org/logos/rust-logo-256x256.png" alt="Image “alt” &amp; &quot; &quot;text&quot; &amp; &lt;stuff&gt; url &lt;em&gt;html&lt;/em&gt; — hard break "></span></label></p>
+<p><label class="checkbox-label"><input class="checkbox-img" type="checkbox"><img src="https://rust-lang.org/logos/rust-logo-256x256.png" title="Some title" alt="Image with title"><span class="img-wrapper"><img src="https://rust-lang.org/logos/rust-logo-256x256.png" title="Some title" alt="Image with title"></span></label></p>

tests/testsuite/print/relative_links/expected/print.html

@@ -13,7 +13,7 @@ <h1 id="testing-relative-links-for-the-print-page"><a class="header" href="#test
 Link <a href="first/alpha/beta.html#anchor">inside but doesn’t exist with anchor</a>.
 Link <a href="first/alpha/gamma.html">inside to html</a>.
 Link <a href="first/alpha/gamma.html#anchor">inside to html with anchor</a>.</p>
-<p><img src="images/picture.png" alt="Some image"></p>
+<p><label class="checkbox-label"><input class="checkbox-img" type="checkbox"><img src="images/picture.png" alt="Some image"><span class="img-wrapper"><img src="images/picture.png" alt="Some image"></span></label></p>
 <p><a href="#first-nested">HTML Link</a></p>
 <img src="images/picture.png" alt="raw html">
 <h2 id="some-section"><a class="header" href="#some-section">Some section</a></h2>