Add PDF two-page spread mode and mobile pinch-to-zoom

Spread mode: new toggle in reader settings renders pages side-by-side
(cover alone, then pairs 2-3, 4-5...) using full screen width. Each
page scales to half the container. Navigation and scroll position
tracking are unchanged since per-page IDs are preserved.

Pinch-to-zoom: captures 2-finger pinch on the PDF reader, blocking
native browser zoom. Live CSS zoom during gesture, snaps to nearest
10% step on release. Single-finger scroll unaffected. applyPdfZoom
moved to module level so touch handlers can call it. Touch listeners
cleaned up on reader close.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

static/css/app.css

@@ -1678,6 +1678,13 @@ body.reader-immersive.reader-show-bottom .reader-overlay  { bottom: var(--bar-h)
 .reader-content.pdf-paginated { overflow:hidden !important; display:flex; align-items:center; justify-content:center; }
 .pdf-paginated .pdf-page-wrapper { margin:0; }
 
+/* PDF two-page spread */
+.pdf-spread-wrapper { display:flex; flex-direction:row; gap:8px; justify-content:center; margin-bottom:1rem; }
+.pdf-spread-wrapper .pdf-page-wrapper { margin:0; }
+.pdf-spread-cover { margin-bottom:1rem; }
+/* Disable text selection during pinch */
+#reader-content.pinch-active { user-select:none; -webkit-user-select:none; }
+
 /* Highlight popover */
 .highlight-popover { position:fixed; z-index:500; display:flex; gap:6px; background:var(--bg-card,#1a1a1a); border:1px solid var(--border); border-radius:var(--radius); padding:6px 8px; box-shadow:0 4px 16px rgba(0,0,0,.5); }
 .hl-color-btn { width:24px; height:24px; border-radius:50%; border:2px solid transparent; cursor:pointer; font-weight:700; font-size:12px; color:#000; line-height:1; }

static/js/app.js

@@ -2700,7 +2700,7 @@ async function _evictBookCache(bookList) {
 
 // Reader settings
 let readerSettings = { fontSize: 16, lineHeight: 1.8, maxWidth: 65, theme: 'dark',
-                        pdfZoom: 100, pdfInverted: false, pdfPaginated: false };
+                        pdfZoom: 100, pdfInverted: false, pdfPaginated: false, pdfSpread: false };
 let readerSettingsPanelOpen = false;
 let currentPdfDoc = null;
 let currentPdfBuffer = null;
@@ -2726,6 +2726,9 @@ let pdfTotalPages = 0;
 let _pdfPageTextBoxCache = {};
 let _pdfRenderGen = 0;
 let _touchStartX = 0;
+let _pinchStartDist = 0;
+let _pinchStartZoom = 100;
+let _isPinching = false;
 
 if (typeof pdfjsLib !== 'undefined') {
   pdfjsLib.GlobalWorkerOptions.workerSrc = '/static/js/pdf.worker.min.js';
@@ -3000,14 +3003,19 @@ async function renderPdf(arrayBuffer, contentEl, scaleOverride) {
   if (scaleOverride == null) pdfVp.style.zoom = readerSettings.pdfZoom / 100;
   contentEl.appendChild(pdfVp);
 
-  const containerWidth = Math.min(contentEl.clientWidth - 32, 900);
+  const containerWidth = readerSettings.pdfSpread
+    ? contentEl.clientWidth - 32
+    : Math.min(contentEl.clientWidth - 32, 900);
+
+  let spreadContainer = null;
 
   for (let pageNum = 1; pageNum <= pdf.numPages; pageNum++) {
     if (_pdfRenderGen !== myGen) { contentEl.innerHTML = ''; return null; }
     const page = await pdf.getPage(pageNum);
     const naturalVp = page.getViewport({scale: 1});
+    const pageWidth = readerSettings.pdfSpread ? (containerWidth - 8) / 2 : containerWidth;
     const scale = scaleOverride != null ? scaleOverride
-      : Math.max(0.5, containerWidth / naturalVp.width);
+      : Math.max(0.5, pageWidth / naturalVp.width);
     const viewport = page.getViewport({scale});
 
     const wrapper = document.createElement('div');
@@ -3028,7 +3036,22 @@ async function renderPdf(arrayBuffer, contentEl, scaleOverride) {
     canvas.style.height = viewport.height + 'px';
     inner.appendChild(canvas);
     wrapper.appendChild(inner);
-    pdfVp.appendChild(wrapper);
+
+    if (!readerSettings.pdfSpread) {
+      pdfVp.appendChild(wrapper);
+    } else if (pageNum === 1) {
+      wrapper.classList.add('pdf-spread-cover');
+      pdfVp.appendChild(wrapper);
+      spreadContainer = null;
+    } else {
+      if (pageNum % 2 === 0) {
+        spreadContainer = document.createElement('div');
+        spreadContainer.className = 'pdf-spread-wrapper';
+        pdfVp.appendChild(spreadContainer);
+      }
+      if (spreadContainer) spreadContainer.appendChild(wrapper);
+      else pdfVp.appendChild(wrapper);
+    }
 
     const ctx = canvas.getContext('2d');
     ctx.scale(dpr, dpr);
@@ -3132,14 +3155,11 @@ async function openBook(bookId) {
     // Apply reader settings (theme, font size, etc.)
     applyReaderSettings(isPdfBook);
 
-    // Swipe for PDF paginated
+    // Touch: swipe (paginated) + pinch-to-zoom
-    contentEl.addEventListener('touchstart', e => { _touchStartX = e.touches[0].clientX; }, {passive: true});
+    contentEl.addEventListener('touchstart',  _pdfTouchStart,  {passive: true});
-    contentEl.addEventListener('touchend', e => {
+    contentEl.addEventListener('touchmove',   _pdfTouchMove,   {passive: false});
-      if (!readerSettings.pdfPaginated) return;
+    contentEl.addEventListener('touchend',    _pdfTouchEnd,    {passive: true});
-      const delta = e.changedTouches[0].clientX - _touchStartX;
+    contentEl.addEventListener('touchcancel', _pdfTouchEnd,    {passive: true});
-      if (delta > 50) pdfGoToPage(pdfCurrentPage - 1);
-      else if (delta < -50) pdfGoToPage(pdfCurrentPage + 1);
-    }, {passive: true});
 
     // Set up progress input
     const progressInput = $('reader-progress-input');
@@ -3405,9 +3425,16 @@ function closeReader() {
   const progressSuffix = $('reader-progress-suffix');
   if (progressSuffix) progressSuffix.textContent = '';
 
-  // Free image blob URLs
+  // Remove touch handlers and free image blob URLs
   const contentEl = $('reader-content');
-  if (contentEl) contentEl.innerHTML = '';
+  if (contentEl) {
+    contentEl.removeEventListener('touchstart',  _pdfTouchStart);
+    contentEl.removeEventListener('touchmove',   _pdfTouchMove);
+    contentEl.removeEventListener('touchend',    _pdfTouchEnd);
+    contentEl.removeEventListener('touchcancel', _pdfTouchEnd);
+    contentEl.classList.remove('pinch-active');
+    contentEl.innerHTML = '';
+  }
   for (const url of Object.values(currentImageMap)) URL.revokeObjectURL(url);
   currentImageMap = {};
 
@@ -3578,6 +3605,7 @@ function toggleSettingsPanel() {
     panel.innerHTML = `
       <label>Zoom <button class="btn btn-sm" id="rs-zoom-minus">−</button> <input type="range" id="rs-zoom" min="50" max="200" step="10" value="${readerSettings.pdfZoom}"> <button class="btn btn-sm" id="rs-zoom-plus">+</button> <span id="rs-zoom-val">${readerSettings.pdfZoom}%</span></label>
       <button class="btn btn-sm ${readerSettings.pdfInverted ? 'active' : ''}" id="rs-invert">Invert</button>
+      <button class="btn btn-sm ${readerSettings.pdfSpread ? 'active' : ''}" id="rs-spread">Spread</button>
     `;
   }
 
@@ -3629,30 +3657,6 @@ function toggleSettingsPanel() {
     });
   } else {
     const zoomRange = panel.querySelector('#rs-zoom');
-    const zoomVal   = panel.querySelector('#rs-zoom-val');
-
-    function applyPdfZoom(newZoom) {
-      const contentEl2 = $('reader-content');
-      // Preserve scroll position across zoom change
-      const fraction = contentEl2
-        ? contentEl2.scrollTop / (contentEl2.scrollHeight - contentEl2.clientHeight || 1)
-        : 0;
-      readerSettings.pdfZoom = newZoom;
-      zoomRange.value = newZoom;
-      zoomVal.textContent = newZoom + '%';
-      saveReaderSettings();
-      if (readerSettings.pdfPaginated) {
-        pdfSmartZoomPage(pdfCurrentPage);
-      } else {
-        const vp = document.getElementById('pdf-viewport');
-        if (vp) vp.style.zoom = readerSettings.pdfZoom / 100;
-        if (contentEl2 && fraction > 0) {
-          requestAnimationFrame(() => {
-            contentEl2.scrollTop = fraction * (contentEl2.scrollHeight - contentEl2.clientHeight);
-          });
-        }
-      }
-    }
 
     zoomRange.addEventListener('input', () => applyPdfZoom(parseInt(zoomRange.value, 10)));
     panel.querySelector('#rs-zoom-minus').addEventListener('click', () =>
@@ -3667,6 +3671,37 @@ function toggleSettingsPanel() {
       saveReaderSettings();
     });
 
+    panel.querySelector('#rs-spread').addEventListener('click', function () {
+      readerSettings.pdfSpread = !readerSettings.pdfSpread;
+      this.classList.toggle('active', readerSettings.pdfSpread);
+      saveReaderSettings();
+      reRenderPdf();
+    });
+
+  }
+}
+
+function applyPdfZoom(newZoom) {
+  const contentEl2 = $('reader-content');
+  const fraction = contentEl2
+    ? contentEl2.scrollTop / (contentEl2.scrollHeight - contentEl2.clientHeight || 1)
+    : 0;
+  readerSettings.pdfZoom = newZoom;
+  const zoomRange = document.getElementById('rs-zoom');
+  const zoomVal = document.getElementById('rs-zoom-val');
+  if (zoomRange) zoomRange.value = newZoom;
+  if (zoomVal) zoomVal.textContent = newZoom + '%';
+  saveReaderSettings();
+  if (readerSettings.pdfPaginated) {
+    pdfSmartZoomPage(pdfCurrentPage);
+  } else {
+    const vp = document.getElementById('pdf-viewport');
+    if (vp) vp.style.zoom = readerSettings.pdfZoom / 100;
+    if (contentEl2 && fraction > 0) {
+      requestAnimationFrame(() => {
+        contentEl2.scrollTop = fraction * (contentEl2.scrollHeight - contentEl2.clientHeight);
+      });
+    }
   }
 }
 
@@ -3724,6 +3759,50 @@ function _pdfPaginatedClick(e) {
   else if (e.clientX > w * 0.6) pdfGoToPage(pdfCurrentPage + 1);
 }
 
+function _pdfTouchStart(e) {
+  if (e.touches.length === 2) {
+    const dx = e.touches[0].clientX - e.touches[1].clientX;
+    const dy = e.touches[0].clientY - e.touches[1].clientY;
+    _pinchStartDist = Math.hypot(dx, dy);
+    _pinchStartZoom = readerSettings.pdfZoom;
+    _isPinching = true;
+    const ce = $('reader-content');
+    if (ce) ce.classList.add('pinch-active');
+  } else {
+    _touchStartX = e.touches[0].clientX;
+    _isPinching = false;
+  }
+}
+
+function _pdfTouchMove(e) {
+  if (e.touches.length !== 2 || !_isPinching) return;
+  e.preventDefault();
+  const dx = e.touches[0].clientX - e.touches[1].clientX;
+  const dy = e.touches[0].clientY - e.touches[1].clientY;
+  const dist = Math.hypot(dx, dy);
+  if (_pinchStartDist === 0) return;
+  const liveZoom = Math.max(50, Math.min(200, _pinchStartZoom * (dist / _pinchStartDist)));
+  const vp = document.getElementById('pdf-viewport');
+  if (vp) vp.style.zoom = liveZoom / 100;
+}
+
+function _pdfTouchEnd(e) {
+  if (_isPinching) {
+    _isPinching = false;
+    const ce = $('reader-content');
+    if (ce) ce.classList.remove('pinch-active');
+    const vp = document.getElementById('pdf-viewport');
+    const liveZoom = vp ? parseFloat(vp.style.zoom) * 100 : readerSettings.pdfZoom;
+    const snapped = Math.max(50, Math.min(200, Math.round(liveZoom / 10) * 10));
+    applyPdfZoom(snapped);
+    return;
+  }
+  if (!readerSettings.pdfPaginated) return;
+  const delta = e.changedTouches[0].clientX - _touchStartX;
+  if (delta > 50) pdfGoToPage(pdfCurrentPage - 1);
+  else if (delta < -50) pdfGoToPage(pdfCurrentPage + 1);
+}
+
 function pdfGoToPage(n) {
   if (!currentPdfDoc) return;
   n = Math.max(1, Math.min(pdfTotalPages, n));