PDF: rerender when scale changes

The fixed-layout renderer now accepts an object for the return value of
`load()` (on the `book.sections` items). If it's an object, the `src`
is the URL of the section, and `onZoom`, if present, will be called
when the viewport is zoomed. With this you can scale the page yourself
rather than relying on the renderer's own scaling with CSS transform.

Also upgraded to PDF.js 4.6.82. And now internal links are broken...
Don't know how to fix that yet.

fixed-layout.js

@@ -56,7 +56,10 @@ export class FixedLayout extends HTMLElement {
 
         this.#observer.observe(this)
     }
-    async #createFrame({ index, src }) {
+    async #createFrame({ index, src: srcOption }) {
+        const srcOptionIsString = typeof srcOption === 'string'
+        const src = srcOptionIsString ? srcOption : srcOption?.src
+        const onZoom = srcOptionIsString ? null : srcOption?.onZoom
         const element = document.createElement('div')
         const iframe = document.createElement('iframe')
         element.append(iframe)
@@ -73,8 +76,7 @@ export class FixedLayout extends HTMLElement {
         this.#root.append(element)
         if (!src) return { blank: true, element, iframe }
         return new Promise(resolve => {
-            const onload = () => {
-                iframe.removeEventListener('load', onload)
+            iframe.addEventListener('load', () => {
                 const doc = iframe.contentDocument
                 this.dispatchEvent(new CustomEvent('load', { detail: { doc, index } }))
                 const { width, height } = getViewport(doc, this.defaultViewport)
@@ -82,9 +84,9 @@ export class FixedLayout extends HTMLElement {
                     element, iframe,
                     width: parseFloat(width),
                     height: parseFloat(height),
+                    onZoom,
                 })
-            }
-            iframe.addEventListener('load', onload)
+            }, { once: true })
             iframe.src = src
         })
     }
@@ -111,11 +113,13 @@ export class FixedLayout extends HTMLElement {
                     right.height ?? blankHeight))
 
         const transform = frame => {
-            const { element, iframe, width, height, blank } = frame
+            let { element, iframe, width, height, blank, onZoom } = frame
+            if (onZoom) onZoom({ doc: frame.iframe.contentDocument, scale })
+            const iframeScale = onZoom ? scale : 1
             Object.assign(iframe.style, {
-                width: `${width}px`,
-                height: `${height}px`,
-                transform: `scale(${scale})`,
+                width: `${width * iframeScale}px`,
+                height: `${height * iframeScale}px`,
+                transform: onZoom ? 'none' : `scale(${scale})`,
                 transformOrigin: 'top left',
                 display: blank ? 'none' : 'block',
             })