Add module for generating quote images

README.md

@@ -340,6 +340,18 @@ These two functions return an object that implements the following interface:
     - `value`: a string; the default value of the parameter
 - `.search(map)`: a function, whose argument is a `Map` whose values are `Map`s (i.e. a two-dimensional map). The first key is the namespace of the search parameter. For non-namespaced parameters, the first key must be `null`. The second key is the parameter's name. Returns a string representing the URL of the search results.
 
+### Generating Images for Quotes
+
+With `quote-image.js`, one can generate shareable images for quotes:
+
+```js
+document.querySelector('foliate-quoteimage').getBlob({
+    title: 'The Time Machine',
+    author: 'H. G. Wells',
+    text: 'Can an instantaneous cube exist?',
+})
+```
+
 ### Supported Browsers
 
 The main use of the library is for use in [Foliate](https://github.com/johnfactotum/foliate), which uses WebKitGTK. As such it's the only engine that has been tested extensively. But it should also work in Chromium and Firefox.

quote-image.js

@@ -0,0 +1,83 @@
+const SVG_NS = 'http://www.w3.org/2000/svg'
+
+// bisect
+const fit = (el, a = 1, b = 50) => {
+    const c = Math.floor(a + (b - a) / 2)
+    el.style.fontSize = `${c}px`
+    if (b - a === 1) return
+    if (el.scrollHeight > el.clientHeight
+    || el.scrollWidth > el.clientWidth) fit(el, a, c)
+    else fit(el, c, b)
+}
+
+const width = 540
+const height = 540
+const pixelRatio = 2
+
+const html = `<style>
+:host {
+    position: absolute;
+    visibility: hidden;
+}
+</style>
+<main style="width: ${width}px; height: ${height}px; overflow: hidden; display: flex; flex-direction: column; justify-content: center; text-align: center; background: #fff; color: #000; font: 16pt serif">
+    <style>
+    .ellipsis {
+        overflow: hidden;
+        display: -webkit-box;
+        -webkit-box-orient: vertical;
+        -webkit-line-clamp: 2;
+        text-overflow: ellipsis;
+    }
+    </style>
+    <div style="font-size: min(4em, 8rem); line-height: 1; margin-bottom: -.5em">“</div>
+    <div id="text" style="margin: 1em; text-wrap: balance"></div>
+    <div style="margin: 0 1em">
+        <div style="font-size: min(.8em, 1.25rem); font-family: sans-serif">
+            <div style="display: block; font-weight: bold; margin-bottom: .25em">
+                <span id="author" class="ellipsis"></span>
+            </div>
+            <div style="display: block; text-wrap: balance">
+                <cite id="title" class="ellipsis"></cite>
+            </div>
+        </div>
+    </div>
+    <div style="height: 1em">&nbsp;</div>
+</main>`
+
+// TODO: lang, vertical writing
+customElements.define('foliate-quoteimage', class extends HTMLElement {
+    #root = this.attachShadow({ mode: 'closed' })
+    constructor() {
+        super()
+        this.#root.innerHTML = html
+    }
+    async getBlob({ title, author, text }) {
+        this.#root.querySelector('#title').textContent = title
+        this.#root.querySelector('#author').textContent = author
+        this.#root.querySelector('#text').innerText = text
+
+        fit(this.#root.querySelector('main'))
+
+        const img = document.createElement('img')
+        return new Promise(resolve => {
+            img.onload = () => {
+                const canvas = document.createElement('canvas')
+                canvas.width = pixelRatio * width
+                canvas.height = pixelRatio * height
+                const ctx = canvas.getContext('2d')
+                ctx.drawImage(img, 0, 0, canvas.width, canvas.height)
+                canvas.toBlob(resolve)
+            }
+            const doc = document.implementation.createDocument(SVG_NS, 'svg')
+            doc.documentElement.setAttribute('viewBox', `0 0 ${width} ${height}`)
+            const obj = doc.createElementNS(SVG_NS, 'foreignObject')
+            obj.setAttribute('width', width)
+            obj.setAttribute('height', height)
+            obj.append(doc.importNode(this.#root.querySelector('main'), true))
+            doc.documentElement.append(obj)
+            img.src = 'data:image/svg+xml;charset=utf-8,'
+                + new XMLSerializer().serializeToString(doc)
+        })
+    }
+})