Add tiled watermark layout support with adjustable gaps and UI controls

docs/tools/add-watermark.md

@@ -33,6 +33,13 @@ Add text or image watermarks to your PDF pages using a visual editor. You can po
 - **Opacity** -- Control image transparency.
 - **Scale** -- Resize the image watermark.
 
+**Layout settings:**
+
+- **Single** -- One watermark per page, positioned by dragging or with the position presets.
+- **Tiled** -- Repeats the watermark across the whole page in a diagonal grid that follows the rotation angle, so the mark covers the document from edge to edge.
+- **Horizontal gap** -- Spacing between tiles along the text direction, as a percentage of the watermark width (tiled mode only).
+- **Vertical gap** -- Spacing between tile rows, as a percentage of the watermark height (tiled mode only).
+
 **General settings:**
 
 - **Apply to all pages** -- When checked, the same watermark applies to every page. Uncheck to set individual watermarks per page.
@@ -43,6 +50,7 @@ Add text or image watermarks to your PDF pages using a visual editor. You can po
 - Visual drag-and-drop positioning on a live PDF preview
 - Resizable watermark with corner handles
 - Text and image watermark modes
+- Single or full-page tiled (repeating) layout with adjustable spacing
 - Per-page or global watermark application
 - Page-by-page navigation in the preview
 - Opacity and rotation controls
@@ -59,6 +67,7 @@ Add text or image watermarks to your PDF pages using a visual editor. You can po
 ## Tips
 
 - For diagonal watermarks across the page, set a rotation around 45 degrees and increase the font size.
+- Tiled mode makes a document much harder to reuse after cropping, since removing one mark still leaves dozens behind. Lower the opacity when tiling so the underlying text stays readable.
 - Image watermarks with transparent backgrounds (PNG format) blend more naturally with the document content.
 - If you need different watermark text on different pages, uncheck "Apply to all pages" and navigate page by page.
 

src/js/logic/add-watermark-page.ts

@@ -11,8 +11,13 @@ import {
   addTextWatermark,
   addImageWatermark,
   parsePageRange,
+  computeTileCenters,
 } from '../utils/pdf-operations.js';
-import { AddWatermarkState, PageWatermarkConfig } from '@/types';
+import {
+  AddWatermarkState,
+  PageWatermarkConfig,
+  WatermarkLayout,
+} from '@/types';
 import * as pdfjsLib from 'pdfjs-dist';
 import { loadPdfWithPasswordPrompt } from '../utils/password-prompt.js';
 import { loadPdfDocument } from '../utils/load-pdf-document.js';
@@ -31,9 +36,15 @@ const pageState: AddWatermarkState = {
   watermarkY: 0.5,
 };
 
+const WATERMARK_FONT_STACK =
+  '"Noto Sans SC", "Noto Sans JP", "Noto Sans KR", "Noto Sans Arabic", Arial, sans-serif';
+
 let watermarkType: 'text' | 'image' = 'text';
+let watermarkLayout: WatermarkLayout = 'single';
 let imageWatermarkDataUrl: string | null = null;
 let imageWatermarkFile: File | null = null;
+let imageWatermarkBitmap: HTMLImageElement | null = null;
+let measureCanvas: HTMLCanvasElement | null = null;
 let isDragging = false;
 let dragOffsetX = 0;
 let dragOffsetY = 0;
@@ -186,6 +197,7 @@ function resetState() {
   pageState.watermarkY = 0.5;
   imageWatermarkDataUrl = null;
   imageWatermarkFile = null;
+  imageWatermarkBitmap = null;
   cachedPdfjsDoc = null;
   currentPageNum = 1;
   totalPageCount = 1;
@@ -273,9 +285,19 @@ async function changePage(newPageNum: number) {
   updateWatermarkOverlay();
 }
 
+function readNumberInput(id: string, fallback: number): number {
+  const input = document.getElementById(id) as HTMLInputElement | null;
+  if (!input) return fallback;
+  const value = parseFloat(input.value);
+  return Number.isFinite(value) ? value : fallback;
+}
+
 function getDefaultConfig(): PageWatermarkConfig {
   return {
     type: 'text',
+    layout: 'single',
+    tileGapX: 25,
+    tileGapY: 75,
     x: 0.5,
     y: 0.5,
     text: '',
@@ -294,6 +316,9 @@ function getDefaultConfig(): PageWatermarkConfig {
 function getCurrentConfig(): PageWatermarkConfig {
   return {
     type: watermarkType,
+    layout: watermarkLayout,
+    tileGapX: readNumberInput('tile-gap-x', 25),
+    tileGapY: readNumberInput('tile-gap-y', 75),
     x: pageState.watermarkX,
     y: pageState.watermarkY,
     text:
@@ -345,11 +370,27 @@ function loadPageConfig(pageNum: number) {
   }
 
   watermarkType = config.type;
+  watermarkLayout = config.layout;
   pageState.watermarkX = config.x;
   pageState.watermarkY = config.y;
+  if (config.imageDataUrl !== imageWatermarkDataUrl) {
+    loadWatermarkBitmap(config.imageDataUrl);
+  }
   imageWatermarkDataUrl = config.imageDataUrl;
   imageWatermarkFile = config.imageFile;
 
+  const tileGapX = document.getElementById('tile-gap-x') as HTMLInputElement;
+  const tileGapY = document.getElementById('tile-gap-y') as HTMLInputElement;
+  const tileGapXValue = document.getElementById('tile-gap-x-value');
+  const tileGapYValue = document.getElementById('tile-gap-y-value');
+
+  if (tileGapX) tileGapX.value = String(config.tileGapX);
+  if (tileGapY) tileGapY.value = String(config.tileGapY);
+  if (tileGapXValue) tileGapXValue.textContent = String(config.tileGapX);
+  if (tileGapYValue) tileGapYValue.textContent = String(config.tileGapY);
+
+  applyLayoutUI();
+
   const typeTextBtn = document.getElementById('type-text-btn');
   const typeImageBtn = document.getElementById('type-image-btn');
   const textOptions = document.getElementById('text-watermark-options');
@@ -511,6 +552,36 @@ function setupEditorControls() {
     updateWatermarkOverlay();
   });
 
+  const layoutSingleBtn = document.getElementById('layout-single-btn');
+  const layoutTileBtn = document.getElementById('layout-tile-btn');
+
+  layoutSingleBtn?.addEventListener('click', () => {
+    watermarkLayout = 'single';
+    applyLayoutUI();
+    updateWatermarkOverlay();
+  });
+
+  layoutTileBtn?.addEventListener('click', () => {
+    watermarkLayout = 'tile';
+    applyLayoutUI();
+    updateWatermarkOverlay();
+  });
+
+  const tileGapX = document.getElementById('tile-gap-x') as HTMLInputElement;
+  const tileGapY = document.getElementById('tile-gap-y') as HTMLInputElement;
+  const tileGapXValue = document.getElementById('tile-gap-x-value');
+  const tileGapYValue = document.getElementById('tile-gap-y-value');
+
+  tileGapX?.addEventListener('input', () => {
+    if (tileGapXValue) tileGapXValue.textContent = tileGapX.value;
+    updateWatermarkOverlay();
+  });
+
+  tileGapY?.addEventListener('input', () => {
+    if (tileGapYValue) tileGapYValue.textContent = tileGapY.value;
+    updateWatermarkOverlay();
+  });
+
   const watermarkText = document.getElementById(
     'watermark-text'
   ) as HTMLInputElement;
@@ -571,6 +642,7 @@ function setupEditorControls() {
     const reader = new FileReader();
     reader.onload = () => {
       imageWatermarkDataUrl = reader.result as string;
+      loadWatermarkBitmap(imageWatermarkDataUrl);
       updateWatermarkOverlay();
     };
     reader.readAsDataURL(file);
@@ -604,6 +676,161 @@ function updatePresetHighlight(x: number, y: number) {
   });
 }
 
+function loadWatermarkBitmap(dataUrl: string | null) {
+  if (!dataUrl) {
+    imageWatermarkBitmap = null;
+    return;
+  }
+  const image = new Image();
+  image.onload = () => {
+    if (imageWatermarkDataUrl !== dataUrl) return;
+    imageWatermarkBitmap = image;
+    updateWatermarkOverlay();
+  };
+  image.src = dataUrl;
+}
+
+function applyLayoutUI() {
+  const singleBtn = document.getElementById('layout-single-btn');
+  const tileBtn = document.getElementById('layout-tile-btn');
+  const tileOptions = document.getElementById('tile-options');
+  const positionSection = document.getElementById('position-section');
+  const dragHint = document.getElementById('drag-hint');
+
+  const activeClass =
+    'flex-1 py-2 px-3 text-sm font-medium rounded-lg bg-indigo-600 text-white transition-colors';
+  const inactiveClass =
+    'flex-1 py-2 px-3 text-sm font-medium rounded-lg bg-gray-700 text-gray-300 hover:bg-gray-600 transition-colors';
+
+  const isTile = watermarkLayout === 'tile';
+  if (singleBtn) singleBtn.className = isTile ? inactiveClass : activeClass;
+  if (tileBtn) tileBtn.className = isTile ? activeClass : inactiveClass;
+  tileOptions?.classList.toggle('hidden', !isTile);
+  positionSection?.classList.toggle('hidden', isTile);
+  dragHint?.classList.toggle('sm:inline', !isTile);
+}
+
+function measureTextWidth(text: string, fontSize: number): number {
+  if (!measureCanvas) measureCanvas = document.createElement('canvas');
+  const ctx = measureCanvas.getContext('2d');
+  if (!ctx) return 0;
+  ctx.font = `bold ${fontSize}px ${WATERMARK_FONT_STACK}`;
+  return ctx.measureText(text).width + 2;
+}
+
+function renderTilePreview() {
+  const canvas = document.getElementById(
+    'tile-preview-canvas'
+  ) as HTMLCanvasElement;
+  const container = document.getElementById('preview-container');
+  if (!canvas || !container) return;
+
+  const displayWidth = container.clientWidth;
+  const displayHeight = container.clientHeight;
+  if (!displayWidth || !displayHeight || !pdfPageWidth || !pdfPageHeight)
+    return;
+
+  const dpr = 2;
+  canvas.width = Math.round(displayWidth * dpr);
+  canvas.height = Math.round(displayHeight * dpr);
+  canvas.style.width = displayWidth + 'px';
+  canvas.style.height = displayHeight + 'px';
+
+  const ctx = canvas.getContext('2d');
+  if (!ctx) return;
+  ctx.clearRect(0, 0, canvas.width, canvas.height);
+  ctx.scale(dpr, dpr);
+
+  const gapX = readNumberInput('tile-gap-x', 25) / 100;
+  const gapY = readNumberInput('tile-gap-y', 75) / 100;
+
+  let itemWidth: number;
+  let itemHeight: number;
+  let uiAngle: number;
+  let opacity: number;
+
+  if (watermarkType === 'text') {
+    const text =
+      (document.getElementById('watermark-text') as HTMLInputElement)?.value ||
+      'CONFIDENTIAL';
+    const fontSize = readNumberInput('font-size', 72);
+    uiAngle = readNumberInput('angle-text', 0);
+    opacity = readNumberInput('opacity-text', 0.3);
+    itemWidth = measureTextWidth(text, fontSize);
+    itemHeight = fontSize * 1.4;
+
+    const centers = computeTileCenters({
+      pageWidth: pdfPageWidth,
+      pageHeight: pdfPageHeight,
+      itemWidth,
+      itemHeight,
+      angle: -uiAngle,
+      gapX,
+      gapY,
+    });
+
+    ctx.globalAlpha = opacity;
+    ctx.fillStyle =
+      (document.getElementById('text-color') as HTMLInputElement)?.value ||
+      '#888888';
+    ctx.font = `bold ${fontSize * previewScale}px ${WATERMARK_FONT_STACK}`;
+    ctx.textAlign = 'center';
+    ctx.textBaseline = 'middle';
+
+    for (const center of centers) {
+      ctx.save();
+      ctx.translate(
+        center.x * previewScale,
+        (pdfPageHeight - center.y) * previewScale
+      );
+      ctx.rotate((uiAngle * Math.PI) / 180);
+      ctx.fillText(text, 0, 0);
+      ctx.restore();
+    }
+    return;
+  }
+
+  const bitmap = imageWatermarkBitmap;
+  if (!bitmap || !bitmap.naturalWidth || !bitmap.naturalHeight) return;
+
+  const scale = readNumberInput('image-scale', 100) / 100;
+  uiAngle = readNumberInput('angle-image', 0);
+  opacity = readNumberInput('opacity-image', 0.3);
+  itemWidth = bitmap.naturalWidth * scale;
+  itemHeight = bitmap.naturalHeight * scale;
+
+  const centers = computeTileCenters({
+    pageWidth: pdfPageWidth,
+    pageHeight: pdfPageHeight,
+    itemWidth,
+    itemHeight,
+    angle: -uiAngle,
+    gapX,
+    gapY,
+  });
+
+  ctx.globalAlpha = opacity;
+  const drawWidth = itemWidth * previewScale;
+  const drawHeight = itemHeight * previewScale;
+
+  for (const center of centers) {
+    ctx.save();
+    ctx.translate(
+      center.x * previewScale,
+      (pdfPageHeight - center.y) * previewScale
+    );
+    ctx.rotate((uiAngle * Math.PI) / 180);
+    ctx.drawImage(
+      bitmap,
+      -drawWidth / 2,
+      -drawHeight / 2,
+      drawWidth,
+      drawHeight
+    );
+    ctx.restore();
+  }
+}
+
 function updateWatermarkOverlay() {
   const box = document.getElementById('watermark-box') as HTMLElement;
   const textOverlay = document.getElementById(
@@ -619,6 +846,18 @@ function updateWatermarkOverlay() {
 
   const containerW = container.clientWidth;
   const containerH = container.clientHeight;
+  const tileCanvas = document.getElementById('tile-preview-canvas');
+
+  if (watermarkLayout === 'tile') {
+    box.classList.add('hidden');
+    textOverlay.classList.add('hidden');
+    imageOverlay.classList.add('hidden');
+    tileCanvas?.classList.remove('hidden');
+    renderTilePreview();
+    return;
+  }
+
+  tileCanvas?.classList.add('hidden');
 
   if (watermarkType === 'text') {
     box.classList.remove('hidden');
@@ -846,6 +1085,9 @@ async function applyWatermark() {
             x: config.x,
             y: posY,
             pageIndices,
+            tile: config.layout === 'tile',
+            tileGapX: config.tileGapX / 100,
+            tileGapY: config.tileGapY / 100,
           })
         );
       } else {
@@ -875,6 +1117,9 @@ async function applyWatermark() {
             x: config.x,
             y: posY,
             pageIndices,
+            tile: config.layout === 'tile',
+            tileGapX: config.tileGapX / 100,
+            tileGapY: config.tileGapY / 100,
           })
         );
       }
@@ -896,6 +1141,9 @@ async function applyWatermark() {
 
         const key = JSON.stringify({
           type: config.type,
+          layout: config.layout,
+          tileGapX: config.tileGapX,
+          tileGapY: config.tileGapY,
           x: config.x,
           y: config.y,
           text: config.text,
@@ -930,6 +1178,9 @@ async function applyWatermark() {
               x: config.x,
               y: posY,
               pageIndices: indices,
+              tile: config.layout === 'tile',
+              tileGapX: config.tileGapX / 100,
+              tileGapY: config.tileGapY / 100,
             })
           );
         } else {
@@ -955,6 +1206,9 @@ async function applyWatermark() {
               x: config.x,
               y: posY,
               pageIndices: indices,
+              tile: config.layout === 'tile',
+              tileGapX: config.tileGapX / 100,
+              tileGapY: config.tileGapY / 100,
             })
           );
         }

src/js/types/add-watermark-type.ts

@@ -9,8 +9,13 @@ export interface AddWatermarkState {
   watermarkY: number; // 0–1, percentage from top (flipped to bottom for PDF)
 }
 
+export type WatermarkLayout = 'single' | 'tile';
+
 export interface PageWatermarkConfig {
   type: 'text' | 'image';
+  layout: WatermarkLayout;
+  tileGapX: number;
+  tileGapY: number;
   x: number;
   y: number;
   text: string;

src/js/utils/pdf-operations.ts

@@ -182,6 +182,82 @@ export function parseDeletePages(str: string, totalPages: number): Set<number> {
   return pages;
 }
 
+export interface TileLayoutOptions {
+  pageWidth: number;
+  pageHeight: number;
+  itemWidth: number;
+  itemHeight: number;
+  angle: number;
+  gapX: number;
+  gapY: number;
+}
+
+export const DEFAULT_TILE_GAP_X = 0.25;
+export const DEFAULT_TILE_GAP_Y = 0.75;
+const MAX_TILES = 1500;
+
+export function computeTileCenters(
+  options: TileLayoutOptions
+): { x: number; y: number }[] {
+  const { pageWidth, pageHeight, itemWidth, itemHeight } = options;
+  if (
+    !(pageWidth > 0) ||
+    !(pageHeight > 0) ||
+    !(itemWidth > 0) ||
+    !(itemHeight > 0) ||
+    !Number.isFinite(options.angle)
+  ) {
+    return [];
+  }
+
+  const rad = (options.angle * Math.PI) / 180;
+  const ux = Math.cos(rad);
+  const uy = Math.sin(rad);
+  const vx = -Math.sin(rad);
+  const vy = Math.cos(rad);
+
+  let stepX = Math.max(itemWidth * (1 + Math.max(0, options.gapX)), 1);
+  let stepY = Math.max(itemHeight * (1 + Math.max(0, options.gapY)), 1);
+
+  const density = (pageWidth * pageHeight) / (stepX * stepY);
+  if (density > MAX_TILES) {
+    const factor = Math.sqrt(density / MAX_TILES);
+    stepX *= factor;
+    stepY *= factor;
+  }
+
+  const centerX = pageWidth / 2;
+  const centerY = pageHeight / 2;
+  const reach = Math.hypot(pageWidth, pageHeight) / 2;
+  const radius = Math.hypot(itemWidth, itemHeight) / 2;
+  const halfExtentX =
+    (Math.abs(ux) * itemWidth + Math.abs(vx) * itemHeight) / 2;
+  const halfExtentY =
+    (Math.abs(uy) * itemWidth + Math.abs(vy) * itemHeight) / 2;
+  const iMax = Math.ceil((reach + radius) / stepX);
+  const jMax = Math.ceil((reach + radius) / stepY);
+
+  const centers: { x: number; y: number }[] = [];
+  for (let j = -jMax; j <= jMax; j++) {
+    for (let i = -iMax; i <= iMax; i++) {
+      const x = centerX + i * stepX * ux + j * stepY * vx;
+      const y = centerY + i * stepX * uy + j * stepY * vy;
+      if (
+        x + halfExtentX < 0 ||
+        x - halfExtentX > pageWidth ||
+        y + halfExtentY < 0 ||
+        y - halfExtentY > pageHeight
+      ) {
+        continue;
+      }
+      centers.push({ x, y });
+      if (centers.length >= MAX_TILES * 2) return centers;
+    }
+  }
+
+  return centers;
+}
+
 export interface TextWatermarkOptions {
   text: string;
   fontSize: number;
@@ -191,6 +267,9 @@ export interface TextWatermarkOptions {
   x?: number;
   y?: number;
   pageIndices?: number[];
+  tile?: boolean;
+  tileGapX?: number;
+  tileGapY?: number;
 }
 
 export async function addTextWatermark(
@@ -244,9 +323,19 @@ export async function addTextWatermark(
     const page = pages[idx];
     if (!page) continue;
     const { width, height } = page.getSize();
-    const cx = posX * width;
-    const cy = posY * height;
+    const centers = options.tile
+      ? computeTileCenters({
+          pageWidth: width,
+          pageHeight: height,
+          itemWidth: imgWidth,
+          itemHeight: imgHeight,
+          angle: options.angle,
+          gapX: options.tileGapX ?? DEFAULT_TILE_GAP_X,
+          gapY: options.tileGapY ?? DEFAULT_TILE_GAP_Y,
+        })
+      : [{ x: posX * width, y: posY * height }];
 
+    for (const { x: cx, y: cy } of centers) {
       page.drawImage(image, {
         x: cx - Math.cos(rad) * halfW + Math.sin(rad) * halfH,
         y: cy - Math.sin(rad) * halfW - Math.cos(rad) * halfH,
@@ -256,6 +345,7 @@ export async function addTextWatermark(
         rotate: degrees(options.angle),
       });
     }
+  }
 
   return new Uint8Array(await pdfDoc.save());
 }
@@ -269,6 +359,9 @@ export interface ImageWatermarkOptions {
   x?: number;
   y?: number;
   pageIndices?: number[];
+  tile?: boolean;
+  tileGapX?: number;
+  tileGapY?: number;
 }
 
 export async function addImageWatermark(
@@ -295,9 +388,19 @@ export async function addImageWatermark(
     const page = pages[idx];
     if (!page) continue;
     const { width, height } = page.getSize();
-    const cx = posX * width;
-    const cy = posY * height;
+    const centers = options.tile
+      ? computeTileCenters({
+          pageWidth: width,
+          pageHeight: height,
+          itemWidth: imgWidth,
+          itemHeight: imgHeight,
+          angle: options.angle,
+          gapX: options.tileGapX ?? DEFAULT_TILE_GAP_X,
+          gapY: options.tileGapY ?? DEFAULT_TILE_GAP_Y,
+        })
+      : [{ x: posX * width, y: posY * height }];
 
+    for (const { x: cx, y: cy } of centers) {
       page.drawImage(image, {
         x: cx - Math.cos(rad) * halfW + Math.sin(rad) * halfH,
         y: cy - Math.sin(rad) * halfW - Math.cos(rad) * halfH,
@@ -307,6 +410,7 @@ export async function addImageWatermark(
         rotate: degrees(options.angle),
       });
     }
+  }
 
   return new Uint8Array(await pdfDoc.save());
 }

src/js/workflow/nodes/watermark-node.ts

@@ -46,6 +46,18 @@ export class WatermarkNode extends BaseWorkflowNode {
       'position',
       new ClassicPreset.InputControl('text', { initial: 'center' })
     );
+    this.addControl(
+      'tile',
+      new ClassicPreset.InputControl('text', { initial: 'no' })
+    );
+    this.addControl(
+      'tileGapX',
+      new ClassicPreset.InputControl('number', { initial: 25 })
+    );
+    this.addControl(
+      'tileGapY',
+      new ClassicPreset.InputControl('number', { initial: 75 })
+    );
     this.addControl(
       'pages',
       new ClassicPreset.InputControl('text', { initial: 'all' })
@@ -96,6 +108,10 @@ export class WatermarkNode extends BaseWorkflowNode {
     const posKey = getText('position', 'center').trim().toLowerCase();
     const { x, y } = positionPresets[posKey] ?? positionPresets['center'];
 
+    const tile = getText('tile', 'no').trim().toLowerCase() === 'yes';
+    const tileGapX = Math.max(0, getNum('tileGapX', 25)) / 100;
+    const tileGapY = Math.max(0, getNum('tileGapY', 75)) / 100;
+
     const pagesStr = getText('pages', 'all').trim().toLowerCase();
     const shouldFlatten =
       getText('flatten', 'no').trim().toLowerCase() === 'yes';
@@ -117,6 +133,9 @@ export class WatermarkNode extends BaseWorkflowNode {
           x,
           y: 1 - y,
           pageIndices,
+          tile,
+          tileGapX,
+          tileGapY,
         });
 
         if (shouldFlatten) {

src/pages/add-watermark.html

@@ -212,7 +212,9 @@
                     <i data-lucide="chevron-right" class="w-4 h-4"></i>
                   </button>
                 </div>
-                <span class="text-xs text-gray-500 hidden sm:inline"
+                <span
+                  id="drag-hint"
+                  class="text-xs text-gray-500 hidden sm:inline"
                   >Drag watermark to position</span
                 >
               </div>
@@ -226,6 +228,10 @@
                   style="touch-action: none"
                 >
                   <canvas id="preview-canvas"></canvas>
+                  <canvas
+                    id="tile-preview-canvas"
+                    class="hidden absolute top-0 left-0 pointer-events-none"
+                  ></canvas>
                   <div
                     id="watermark-box"
                     class="absolute pointer-events-auto"
@@ -284,6 +290,29 @@
                 </button>
               </div>
 
+              <div>
+                <label class="block mb-1.5 text-sm font-medium text-gray-300"
+                  >Layout</label
+                >
+                <div class="flex gap-2">
+                  <button
+                    id="layout-single-btn"
+                    class="flex-1 py-2 px-3 text-sm font-medium rounded-lg bg-indigo-600 text-white transition-colors"
+                  >
+                    Single
+                  </button>
+                  <button
+                    id="layout-tile-btn"
+                    class="flex-1 py-2 px-3 text-sm font-medium rounded-lg bg-gray-700 text-gray-300 hover:bg-gray-600 transition-colors"
+                  >
+                    Tiled
+                  </button>
+                </div>
+                <p class="text-xs text-gray-500 mt-1.5">
+                  Tiled repeats the watermark across the whole page.
+                </p>
+              </div>
+
               <div
                 class="flex items-center gap-2 bg-gray-900 rounded-lg px-3 py-2"
               >
@@ -470,7 +499,44 @@
                 </div>
               </div>
 
+              <div id="tile-options" class="hidden space-y-4">
                 <div>
+                  <label
+                    for="tile-gap-x"
+                    class="block mb-1.5 text-sm font-medium text-gray-300"
+                  >
+                    Horizontal gap: <span id="tile-gap-x-value">25</span>%
+                  </label>
+                  <input
+                    type="range"
+                    id="tile-gap-x"
+                    min="0"
+                    max="200"
+                    step="5"
+                    value="25"
+                    class="w-full h-2 bg-gray-700 rounded-lg cursor-pointer accent-indigo-500"
+                  />
+                </div>
+                <div>
+                  <label
+                    for="tile-gap-y"
+                    class="block mb-1.5 text-sm font-medium text-gray-300"
+                  >
+                    Vertical gap: <span id="tile-gap-y-value">75</span>%
+                  </label>
+                  <input
+                    type="range"
+                    id="tile-gap-y"
+                    min="0"
+                    max="200"
+                    step="5"
+                    value="75"
+                    class="w-full h-2 bg-gray-700 rounded-lg cursor-pointer accent-indigo-500"
+                  />
+                </div>
+              </div>
+
+              <div id="position-section">
                 <label class="block mb-1.5 text-sm font-medium text-gray-300"
                   >Position</label
                 >

src/tests/watermark-tile.test.ts

@@ -0,0 +1,391 @@
+import { describe, it, expect } from 'vitest';
+import {
+  computeTileCenters,
+  addImageWatermark,
+} from '../js/utils/pdf-operations';
+import {
+  PDFArray,
+  PDFDocument,
+  PDFName,
+  PDFObject,
+  PDFRawStream,
+  PDFRef,
+} from 'pdf-lib';
+import { inflateSync } from 'node:zlib';
+
+const PNG_1X1_BASE64 =
+  'iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mP8z8BQDwAEhQGAhKmMIQAAAABJRU5ErkJggg==';
+
+function pngBytes(): Uint8Array {
+  return new Uint8Array(Buffer.from(PNG_1X1_BASE64, 'base64'));
+}
+
+async function createTestPdf(pageCount: number): Promise<Uint8Array> {
+  const doc = await PDFDocument.create();
+  for (let i = 0; i < pageCount; i++) {
+    doc.addPage([612, 792]);
+  }
+  return new Uint8Array(await doc.save());
+}
+
+function resolve(doc: PDFDocument, ref?: PDFObject): PDFObject | undefined {
+  if (ref instanceof PDFRef) {
+    return doc.context.lookup(ref) as PDFObject | undefined;
+  }
+  return ref;
+}
+
+function decodeStream(doc: PDFDocument, ref?: PDFObject): string {
+  const stream = resolve(doc, ref);
+  if (!(stream instanceof PDFRawStream)) return '';
+  const raw = Buffer.from(stream.contents);
+  const filter = stream.dict.get(PDFName.of('Filter'));
+  return filter?.toString().includes('FlateDecode')
+    ? inflateSync(raw).toString('latin1')
+    : raw.toString('latin1');
+}
+
+async function countDrawOpsPerPage(bytes: Uint8Array): Promise<number[]> {
+  const doc = await PDFDocument.load(bytes);
+  return doc.getPages().map((page) => {
+    const contents = page.node.get(PDFName.of('Contents'));
+    const resolved = doc.context.lookup(contents);
+    const parts =
+      resolved instanceof PDFArray
+        ? resolved.asArray().map((entry) => decodeStream(doc, entry))
+        : [decodeStream(doc, contents)];
+    return parts.join('\n').match(/\/[^\s/[\]<>()]+\s+Do\b/g)?.length ?? 0;
+  });
+}
+
+async function countDrawOps(bytes: Uint8Array): Promise<number> {
+  const perPage = await countDrawOpsPerPage(bytes);
+  return perPage.reduce((sum, n) => sum + n, 0);
+}
+
+describe('computeTileCenters', () => {
+  const page = { pageWidth: 612, pageHeight: 792 };
+
+  it('produces a single-row-and-column-aligned grid at angle 0', () => {
+    const centers = computeTileCenters({
+      ...page,
+      itemWidth: 100,
+      itemHeight: 100,
+      angle: 0,
+      gapX: 0,
+      gapY: 0,
+    });
+
+    expect(centers.length).toBeGreaterThan(1);
+
+    const xs = [...new Set(centers.map((c) => Math.round(c.x)))].sort(
+      (a, b) => a - b
+    );
+    const ys = [...new Set(centers.map((c) => Math.round(c.y)))].sort(
+      (a, b) => a - b
+    );
+
+    for (let i = 1; i < xs.length; i++) expect(xs[i] - xs[i - 1]).toBe(100);
+    for (let i = 1; i < ys.length; i++) expect(ys[i] - ys[i - 1]).toBe(100);
+    expect(centers.length).toBe(xs.length * ys.length);
+  });
+
+  it('covers the whole page including all four corners', () => {
+    const centers = computeTileCenters({
+      ...page,
+      itemWidth: 200,
+      itemHeight: 60,
+      angle: 45,
+      gapX: 0.2,
+      gapY: 0.5,
+    });
+
+    const radius = Math.hypot(200, 60) / 2;
+    const corners = [
+      { x: 0, y: 0 },
+      { x: 612, y: 0 },
+      { x: 0, y: 792 },
+      { x: 612, y: 792 },
+    ];
+
+    for (const corner of corners) {
+      const nearest = Math.min(
+        ...centers.map((c) => Math.hypot(c.x - corner.x, c.y - corner.y))
+      );
+      expect(nearest).toBeLessThanOrEqual(radius);
+    }
+  });
+
+  it('keeps every tile within reach of the page', () => {
+    const centers = computeTileCenters({
+      ...page,
+      itemWidth: 150,
+      itemHeight: 50,
+      angle: -45,
+      gapX: 0.25,
+      gapY: 0.75,
+    });
+
+    const cos = Math.abs(Math.cos((-45 * Math.PI) / 180));
+    const sin = Math.abs(Math.sin((-45 * Math.PI) / 180));
+    const halfExtentX = (cos * 150 + sin * 50) / 2;
+    const halfExtentY = (sin * 150 + cos * 50) / 2;
+
+    for (const c of centers) {
+      expect(c.x).toBeGreaterThanOrEqual(-halfExtentX);
+      expect(c.x).toBeLessThanOrEqual(612 + halfExtentX);
+      expect(c.y).toBeGreaterThanOrEqual(-halfExtentY);
+      expect(c.y).toBeLessThanOrEqual(792 + halfExtentY);
+    }
+  });
+
+  it('is symmetric about the page center', () => {
+    const centers = computeTileCenters({
+      ...page,
+      itemWidth: 120,
+      itemHeight: 40,
+      angle: 30,
+      gapX: 0.5,
+      gapY: 0.5,
+    });
+
+    const keys = new Set(
+      centers.map((c) => `${c.x.toFixed(3)}:${c.y.toFixed(3)}`)
+    );
+    for (const c of centers) {
+      const mirrorX = (612 - c.x).toFixed(3);
+      const mirrorY = (792 - c.y).toFixed(3);
+      expect(keys.has(`${mirrorX}:${mirrorY}`)).toBe(true);
+    }
+  });
+
+  it('spaces tiles further apart as the gap grows', () => {
+    const tight = computeTileCenters({
+      ...page,
+      itemWidth: 100,
+      itemHeight: 40,
+      angle: -45,
+      gapX: 0,
+      gapY: 0,
+    });
+    const loose = computeTileCenters({
+      ...page,
+      itemWidth: 100,
+      itemHeight: 40,
+      angle: -45,
+      gapX: 1,
+      gapY: 2,
+    });
+
+    expect(loose.length).toBeLessThan(tight.length);
+    expect(loose.length).toBeGreaterThan(0);
+  });
+
+  it('treats negative gaps as zero', () => {
+    const negative = computeTileCenters({
+      ...page,
+      itemWidth: 100,
+      itemHeight: 40,
+      angle: 0,
+      gapX: -5,
+      gapY: -5,
+    });
+    const zero = computeTileCenters({
+      ...page,
+      itemWidth: 100,
+      itemHeight: 40,
+      angle: 0,
+      gapX: 0,
+      gapY: 0,
+    });
+
+    expect(negative).toEqual(zero);
+  });
+
+  it('caps the tile count for tiny watermarks', () => {
+    const centers = computeTileCenters({
+      ...page,
+      itemWidth: 1,
+      itemHeight: 1,
+      angle: 0,
+      gapX: 0,
+      gapY: 0,
+    });
+
+    expect(centers.length).toBeGreaterThan(0);
+    expect(centers.length).toBeLessThanOrEqual(3000);
+  });
+
+  it('stays bounded for extreme aspect ratios', () => {
+    const wide = computeTileCenters({
+      ...page,
+      itemWidth: 5000,
+      itemHeight: 2,
+      angle: 17,
+      gapX: 0,
+      gapY: 0,
+    });
+    const tall = computeTileCenters({
+      ...page,
+      itemWidth: 1,
+      itemHeight: 5000,
+      angle: 0,
+      gapX: 0,
+      gapY: 0,
+    });
+
+    for (const centers of [wide, tall]) {
+      expect(centers.length).toBeGreaterThan(0);
+      expect(centers.length).toBeLessThanOrEqual(3000);
+      expect(
+        centers.every((c) => Number.isFinite(c.x) && Number.isFinite(c.y))
+      ).toBe(true);
+    }
+  });
+
+  it('ignores a non-finite angle', () => {
+    expect(
+      computeTileCenters({
+        ...page,
+        itemWidth: 100,
+        itemHeight: 40,
+        angle: Number.NaN,
+        gapX: 0,
+        gapY: 0,
+      })
+    ).toEqual([]);
+  });
+
+  it('returns nothing for degenerate input', () => {
+    expect(
+      computeTileCenters({
+        pageWidth: 0,
+        pageHeight: 792,
+        itemWidth: 10,
+        itemHeight: 10,
+        angle: 0,
+        gapX: 0,
+        gapY: 0,
+      })
+    ).toEqual([]);
+
+    expect(
+      computeTileCenters({
+        ...page,
+        itemWidth: 0,
+        itemHeight: 10,
+        angle: 0,
+        gapX: 0,
+        gapY: 0,
+      })
+    ).toEqual([]);
+
+    expect(
+      computeTileCenters({
+        ...page,
+        itemWidth: Number.NaN,
+        itemHeight: 10,
+        angle: 0,
+        gapX: 0,
+        gapY: 0,
+      })
+    ).toEqual([]);
+
+    expect(
+      computeTileCenters({
+        ...page,
+        itemWidth: -10,
+        itemHeight: 10,
+        angle: 0,
+        gapX: 0,
+        gapY: 0,
+      })
+    ).toEqual([]);
+  });
+});
+
+describe('addImageWatermark tiling', () => {
+  it('draws the watermark once per page in single mode', async () => {
+    const result = await addImageWatermark(await createTestPdf(2), {
+      imageBytes: pngBytes(),
+      imageType: 'png',
+      opacity: 0.3,
+      angle: -45,
+      scale: 100,
+    });
+
+    expect(await countDrawOps(result)).toBe(2);
+  });
+
+  it('repeats the watermark across each page in tile mode', async () => {
+    const single = await addImageWatermark(await createTestPdf(1), {
+      imageBytes: pngBytes(),
+      imageType: 'png',
+      opacity: 0.3,
+      angle: -45,
+      scale: 100,
+    });
+    const tiled = await addImageWatermark(await createTestPdf(1), {
+      imageBytes: pngBytes(),
+      imageType: 'png',
+      opacity: 0.3,
+      angle: -45,
+      scale: 100,
+      tile: true,
+      tileGapX: 0.25,
+      tileGapY: 0.75,
+    });
+
+    expect(await countDrawOps(single)).toBe(1);
+    expect(await countDrawOps(tiled)).toBeGreaterThan(10);
+  });
+
+  it('only tiles the selected pages', async () => {
+    const tiled = await addImageWatermark(await createTestPdf(3), {
+      imageBytes: pngBytes(),
+      imageType: 'png',
+      opacity: 0.3,
+      angle: 0,
+      scale: 100,
+      pageIndices: [1],
+      tile: true,
+      tileGapX: 0.25,
+      tileGapY: 0.75,
+    });
+
+    const doc = await PDFDocument.load(tiled);
+    expect(doc.getPageCount()).toBe(3);
+    const perPage = await countDrawOpsPerPage(tiled);
+    expect(perPage[0]).toBe(0);
+    expect(perPage[1]).toBeGreaterThan(10);
+    expect(perPage[2]).toBe(0);
+
+    const untouched = await addImageWatermark(await createTestPdf(3), {
+      imageBytes: pngBytes(),
+      imageType: 'png',
+      opacity: 0.3,
+      angle: 0,
+      scale: 100,
+      pageIndices: [],
+      tile: true,
+    });
+    expect(await countDrawOps(untouched)).toBe(0);
+  });
+
+  it('produces a loadable PDF with a bounded size when tiling', async () => {
+    const tiled = await addImageWatermark(await createTestPdf(5), {
+      imageBytes: pngBytes(),
+      imageType: 'png',
+      opacity: 0.2,
+      angle: -45,
+      scale: 20,
+      tile: true,
+      tileGapX: 0,
+      tileGapY: 0,
+    });
+
+    const doc = await PDFDocument.load(tiled);
+    expect(doc.getPageCount()).toBe(5);
+    expect(tiled.byteLength).toBeLessThan(5 * 1024 * 1024);
+  });
+});