Get the text under highlight/squiggly/underline/strikethrough annotations (bug 1885505)

and add an invisible element containing the text in the annotation layer to make
it readable by a screen reader.

src/core/annotation.js

@@ -1247,6 +1247,10 @@ class Annotation {
     return null;
   }
 
+  get overlaysTextContent() {
+    return false;
+  }
+
   get hasTextContent() {
     return false;
   }
@@ -4711,6 +4715,10 @@ class HighlightAnnotation extends MarkupAnnotation {
     }
   }
 
+  get overlaysTextContent() {
+    return true;
+  }
+
   static createNewDict(annotation, xref, { apRef, ap }) {
     const { color, oldAnnotation, opacity, rect, rotation, user, quadPoints } =
       annotation;
@@ -4835,6 +4843,10 @@ class UnderlineAnnotation extends MarkupAnnotation {
       this.data.popupRef = null;
     }
   }
+
+  get overlaysTextContent() {
+    return true;
+  }
 }
 
 class SquigglyAnnotation extends MarkupAnnotation {
@@ -4879,6 +4891,10 @@ class SquigglyAnnotation extends MarkupAnnotation {
       this.data.popupRef = null;
     }
   }
+
+  get overlaysTextContent() {
+    return true;
+  }
 }
 
 class StrikeOutAnnotation extends MarkupAnnotation {
@@ -4918,6 +4934,10 @@ class StrikeOutAnnotation extends MarkupAnnotation {
       this.data.popupRef = null;
     }
   }
+
+  get overlaysTextContent() {
+    return true;
+  }
 }
 
 class StampAnnotation extends MarkupAnnotation {

src/core/document.js

@@ -66,6 +66,7 @@ import { calculateMD5 } from "./calculate_md5.js";
 import { Catalog } from "./catalog.js";
 import { clearGlobalCaches } from "./cleanup_helper.js";
 import { DatasetReader } from "./dataset_reader.js";
+import { Intersector } from "./intersector.js";
 import { Linearization } from "./parser.js";
 import { NullStream } from "./stream.js";
 import { ObjectLoader } from "./object_loader.js";
@@ -632,6 +633,7 @@ class Page {
     includeMarkedContent,
     disableNormalization,
     sink,
+    intersector = null,
   }) {
     const contentStreamPromise = this.getContentStream();
     const resourcesPromise = this.loadResources(RESOURCES_KEYS_TEXT_CONTENT);
@@ -658,6 +660,7 @@ class Page {
       sink,
       viewBox: this.view,
       lang,
+      intersector,
     });
   }
 
@@ -707,6 +710,8 @@ class Page {
       intentDisplay = !!(intent & RenderingIntentFlag.DISPLAY),
       intentPrint = !!(intent & RenderingIntentFlag.PRINT);
 
+    const highlightedAnnotations = [];
+
     for (const annotation of annotations) {
       // Get the annotation even if it's hidden because
       // JS can change its display.
@@ -732,9 +737,29 @@ class Page {
               );
             })
         );
+      } else if (annotation.overlaysTextContent && isVisible) {
+        highlightedAnnotations.push(annotation);
       }
     }
 
+    if (highlightedAnnotations.length > 0) {
+      const intersector = new Intersector(highlightedAnnotations);
+      textContentPromises.push(
+        this.extractTextContent({
+          handler,
+          task,
+          includeMarkedContent: false,
+          disableNormalization: false,
+          sink: null,
+          viewBox: this.view,
+          lang: null,
+          intersector,
+        }).then(() => {
+          intersector.setText();
+        })
+      );
+    }
+
     await Promise.all(textContentPromises);
     return annotationsData;
   }

src/core/evaluator.js

@@ -2362,6 +2362,7 @@ class PartialEvaluator {
     disableNormalization = false,
     keepWhiteSpace = false,
     prevRefs = null,
+    intersector = null,
   }) {
     const objId = stream.dict?.objId;
     const seenRefs = new RefSet(prevRefs);
@@ -2506,6 +2507,7 @@ class PartialEvaluator {
       transform = textContentItem.prevTransform,
       fontName = textContentItem.fontName,
     }) {
+      intersector?.addExtraChar(" ");
       textContent.items.push({
         str: " ",
         dir: "ltr",
@@ -2964,9 +2966,21 @@ class PartialEvaluator {
 
         if (!font.vertical) {
           scaledDim *= textState.textHScale;
+          intersector?.addGlyph(
+            getCurrentTextTransform(),
+            scaledDim,
+            0,
+            glyph.unicode
+          );
           textState.translateTextMatrix(scaledDim, 0);
           textChunk.width += scaledDim;
         } else {
+          intersector?.addGlyph(
+            getCurrentTextTransform(),
+            0,
+            scaledDim,
+            glyph.unicode
+          );
           textState.translateTextMatrix(0, scaledDim);
           scaledDim = Math.abs(scaledDim);
           textChunk.height += scaledDim;
@@ -2985,8 +2999,12 @@ class PartialEvaluator {
           // alignment issues between the textLayer and the canvas if the text
           // contains e.g. tabs (fixes issue6612.pdf).
           textChunk.str.push(" ");
+          intersector?.addExtraChar(" ");
+        }
+
+        if (!intersector) {
+          textChunk.str.push(glyphUnicode);
         }
-        textChunk.str.push(glyphUnicode);
 
         if (charSpacing) {
           if (!font.vertical) {
@@ -3002,6 +3020,7 @@ class PartialEvaluator {
     }
 
     function appendEOL() {
+      intersector?.addExtraChar("\n");
       resetLastChars();
       if (textContentItem.initialized) {
         textContentItem.hasEOL = true;
@@ -3027,6 +3046,7 @@ class PartialEvaluator {
         if (textContentItem.initialized) {
           resetLastChars();
           textContentItem.str.push(" ");
+          intersector?.addExtraChar(" ");
         }
         return false;
       }
@@ -3078,7 +3098,7 @@ class PartialEvaluator {
       if (batch && length < TEXT_CHUNK_BATCH_SIZE) {
         return;
       }
-      sink.enqueue(textContent, length);
+      sink?.enqueue(textContent, length);
       textContent.items = [];
       textContent.styles = Object.create(null);
     }
@@ -3088,7 +3108,7 @@ class PartialEvaluator {
     return new Promise(function promiseBody(resolve, reject) {
       const next = function (promise) {
         enqueueChunk(/* batch = */ true);
-        Promise.all([promise, sink.ready]).then(function () {
+        Promise.all([promise, sink?.ready]).then(function () {
           try {
             promiseBody(resolve, reject);
           } catch (ex) {
@@ -3341,7 +3361,7 @@ class PartialEvaluator {
                   },
 
                   get desiredSize() {
-                    return sink.desiredSize;
+                    return sink.desiredSize ?? 0;
                   },
 
                   get ready() {
@@ -3359,7 +3379,7 @@ class PartialEvaluator {
                         : resources,
                     stateManager: xObjStateManager,
                     includeMarkedContent,
-                    sink: sinkWrapper,
+                    sink: sink && sinkWrapper,
                     seenStyles,
                     viewBox,
                     lang,
@@ -3499,7 +3519,7 @@ class PartialEvaluator {
             }
             break;
         } // switch
-        if (textContent.items.length >= sink.desiredSize) {
+        if (textContent.items.length >= (sink?.desiredSize ?? 1)) {
           // Wait for ready, if we reach highWaterMark.
           stop = true;
           break;

src/core/intersector.js

@@ -0,0 +1,203 @@
+/* Copyright 2025 Mozilla Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+class SingleIntersector {
+  #annotation;
+
+  #minX = Infinity;
+
+  #minY = Infinity;
+
+  #maxX = -Infinity;
+
+  #maxY = -Infinity;
+
+  #quadPoints;
+
+  #text = [];
+
+  #extraChars = [];
+
+  #lastIntersectingQuadIndex = -1;
+
+  #canTakeExtraChars = false;
+
+  constructor(annotation) {
+    this.#annotation = annotation;
+    const quadPoints = (this.#quadPoints = annotation.data.quadPoints);
+
+    for (let i = 0, ii = quadPoints.length; i < ii; i += 8) {
+      this.#minX = Math.min(this.#minX, quadPoints[i]);
+      this.#maxX = Math.max(this.#maxX, quadPoints[i + 2]);
+      this.#minY = Math.min(this.#minY, quadPoints[i + 5]);
+      this.#maxY = Math.max(this.#maxY, quadPoints[i + 1]);
+    }
+  }
+
+  overlaps(other) {
+    return !(
+      this.#minX >= other.#maxX ||
+      this.#maxX <= other.#minX ||
+      this.#minY >= other.#maxY ||
+      this.#maxY <= other.#minY
+    );
+  }
+
+  /**
+   * Check if the given point intersects with the annotation's quad points.
+   * The point (x, y) is supposed to be the center of the glyph.
+   * @param {number} x
+   * @param {number} y
+   * @returns {boolean}
+   */
+  #intersects(x, y) {
+    if (
+      this.#minX >= x ||
+      this.#maxX <= x ||
+      this.#minY >= y ||
+      this.#maxY <= y
+    ) {
+      return false;
+    }
+
+    const quadPoints = this.#quadPoints;
+    if (quadPoints.length === 8) {
+      // We've only one quad, so if we intersect min/max bounds then we
+      // intersect the quad.
+      return true;
+    }
+
+    if (this.#lastIntersectingQuadIndex >= 0) {
+      const i = this.#lastIntersectingQuadIndex;
+      if (
+        !(
+          quadPoints[i] >= x ||
+          quadPoints[i + 2] <= x ||
+          quadPoints[i + 5] >= y ||
+          quadPoints[i + 1] <= y
+        )
+      ) {
+        return true;
+      }
+      this.#lastIntersectingQuadIndex = -1;
+    }
+
+    for (let i = 0, ii = quadPoints.length; i < ii; i += 8) {
+      if (
+        !(
+          quadPoints[i] >= x ||
+          quadPoints[i + 2] <= x ||
+          quadPoints[i + 5] >= y ||
+          quadPoints[i + 1] <= y
+        )
+      ) {
+        this.#lastIntersectingQuadIndex = i;
+        return true;
+      }
+    }
+    return false;
+  }
+
+  addGlyph(x, y, glyph) {
+    if (!this.#intersects(x, y)) {
+      this.disableExtraChars();
+      return false;
+    }
+
+    if (this.#extraChars.length > 0) {
+      this.#text.push(this.#extraChars.join(""));
+      this.#extraChars.length = 0;
+    }
+    this.#text.push(glyph);
+    this.#canTakeExtraChars = true;
+
+    return true;
+  }
+
+  addExtraChar(char) {
+    if (this.#canTakeExtraChars) {
+      this.#extraChars.push(char);
+    }
+  }
+
+  disableExtraChars() {
+    if (!this.#canTakeExtraChars) {
+      return;
+    }
+    this.#canTakeExtraChars = false;
+    this.#extraChars.length = 0;
+  }
+
+  setText() {
+    this.#annotation.data.overlaidText = this.#text.join("");
+  }
+}
+
+class Intersector {
+  #intersectors = new Map();
+
+  constructor(annotations) {
+    for (const annotation of annotations) {
+      if (!annotation.data.quadPoints) {
+        continue;
+      }
+      const intersector = new SingleIntersector(annotation);
+      for (const [otherIntersector, overlapping] of this.#intersectors) {
+        if (otherIntersector.overlaps(intersector)) {
+          if (!overlapping) {
+            this.#intersectors.set(otherIntersector, new Set([intersector]));
+          } else {
+            overlapping.add(intersector);
+          }
+        }
+      }
+      this.#intersectors.set(intersector, null);
+    }
+  }
+
+  addGlyph(transform, width, height, glyph) {
+    const x = transform[4] + width / 2;
+    const y = transform[5] + height / 2;
+    let overlappingIntersectors;
+    for (const [intersector, overlapping] of this.#intersectors) {
+      if (overlappingIntersectors) {
+        if (overlappingIntersectors.has(intersector)) {
+          intersector.addGlyph(x, y, glyph);
+        } else {
+          intersector.disableExtraChars();
+        }
+        continue;
+      }
+      if (!intersector.addGlyph(x, y, glyph)) {
+        continue;
+      }
+      overlappingIntersectors = overlapping;
+    }
+  }
+
+  addExtraChar(char) {
+    for (const intersector of this.#intersectors.keys()) {
+      intersector.addExtraChar(char);
+    }
+  }
+
+  setText() {
+    for (const intersector of this.#intersectors.keys()) {
+      intersector.setText();
+    }
+  }
+}
+
+export { Intersector };

src/display/annotation_layer.js

@@ -555,6 +555,7 @@ class AnnotationElement {
     svg.classList.add("quadrilateralsContainer");
     svg.setAttribute("width", 0);
     svg.setAttribute("height", 0);
+    svg.role = "none";
     const defs = svgFactory.createElement("defs");
     svg.append(defs);
     const clipPath = svgFactory.createElement("clipPath");
@@ -2912,13 +2913,23 @@ class HighlightAnnotationElement extends AnnotationElement {
   }
 
   render() {
-    if (!this.data.popupRef && this.hasPopupData) {
+    const {
+      data: { overlaidText, popupRef },
+    } = this;
+    if (!popupRef && this.hasPopupData) {
       this._createPopup();
     }
 
     this.container.classList.add("highlightAnnotation");
     this._editOnDoubleClick();
 
+    if (overlaidText) {
+      const mark = document.createElement("mark");
+      mark.classList.add("overlaidText");
+      mark.textContent = overlaidText;
+      this.container.append(mark);
+    }
+
     return this.container;
   }
 }
@@ -2933,11 +2944,22 @@ class UnderlineAnnotationElement extends AnnotationElement {
   }
 
   render() {
-    if (!this.data.popupRef && this.hasPopupData) {
+    const {
+      data: { overlaidText, popupRef },
+    } = this;
+    if (!popupRef && this.hasPopupData) {
       this._createPopup();
     }
 
     this.container.classList.add("underlineAnnotation");
+
+    if (overlaidText) {
+      const underline = document.createElement("u");
+      underline.classList.add("overlaidText");
+      underline.textContent = overlaidText;
+      this.container.append(underline);
+    }
+
     return this.container;
   }
 }
@@ -2952,11 +2974,22 @@ class SquigglyAnnotationElement extends AnnotationElement {
   }
 
   render() {
-    if (!this.data.popupRef && this.hasPopupData) {
+    const {
+      data: { overlaidText, popupRef },
+    } = this;
+    if (!popupRef && this.hasPopupData) {
       this._createPopup();
     }
 
     this.container.classList.add("squigglyAnnotation");
+
+    if (overlaidText) {
+      const underline = document.createElement("u");
+      underline.classList.add("overlaidText");
+      underline.textContent = overlaidText;
+      this.container.append(underline);
+    }
+
     return this.container;
   }
 }
@@ -2971,11 +3004,22 @@ class StrikeOutAnnotationElement extends AnnotationElement {
   }
 
   render() {
-    if (!this.data.popupRef && this.hasPopupData) {
+    const {
+      data: { overlaidText, popupRef },
+    } = this;
+    if (!popupRef && this.hasPopupData) {
       this._createPopup();
     }
 
     this.container.classList.add("strikeoutAnnotation");
+
+    if (overlaidText) {
+      const strikeout = document.createElement("s");
+      strikeout.classList.add("overlaidText");
+      strikeout.textContent = overlaidText;
+      this.container.append(strikeout);
+    }
+
     return this.container;
   }
 }

test/integration/annotation_spec.mjs

@@ -696,4 +696,77 @@ describe("ResetForm action", () => {
       });
     });
   });
+
+  describe("Text under some annotations", () => {
+    describe("bug1885505.pdf", () => {
+      let pages;
+
+      beforeEach(async () => {
+        pages = await loadAndWait(
+          "bug1885505.pdf",
+          ":is(" +
+            [56, 58, 60, 65]
+              .map(id => `[data-annotation-id='${id}R']`)
+              .join(", ") +
+            ")"
+        );
+      });
+
+      afterEach(async () => {
+        await closePages(pages);
+      });
+
+      it("must check that the text under a highlight annotation exist in the DOM", async () => {
+        await Promise.all(
+          pages.map(async ([browserName, page]) => {
+            const text = await page.$eval(
+              "[data-annotation-id='56R'] mark",
+              el => el.textContent
+            );
+            expect(text).withContext(`In ${browserName}`).toEqual("Languages");
+          })
+        );
+      });
+
+      it("must check that the text under an underline annotation exist in the DOM", async () => {
+        await Promise.all(
+          pages.map(async ([browserName, page]) => {
+            const text = await page.$eval(
+              "[data-annotation-id='58R'] u",
+              el => el.textContent
+            );
+            expect(text).withContext(`In ${browserName}`).toEqual("machine");
+          })
+        );
+      });
+
+      it("must check that the text under a squiggly annotation exist in the DOM", async () => {
+        await Promise.all(
+          pages.map(async ([browserName, page]) => {
+            const text = await page.$eval(
+              "[data-annotation-id='60R'] u",
+              el => el.textContent
+            );
+            expect(text).withContext(`In ${browserName}`)
+              .toEqual(`paths through nested loops. We have implemented
+a dynamic compiler for JavaScript based on our`);
+          })
+        );
+      });
+
+      it("must check that the text under a strikeout annotation exist in the DOM", async () => {
+        await Promise.all(
+          pages.map(async ([browserName, page]) => {
+            const text = await page.$eval(
+              "[data-annotation-id='65R'] s",
+              el => el.textContent
+            );
+            expect(text)
+              .withContext(`In ${browserName}`)
+              .toEqual("Experimentation,");
+          })
+        );
+      });
+    });
+  });
 });

test/pdfs/.gitignore

@@ -727,3 +727,4 @@
 !bug1963407.pdf
 !issue19517.pdf
 !empty#hash.pdf
+!bug1885505.pdf

test/unit/api_spec.js

@@ -5127,4 +5127,47 @@ Caron Broadcasting, Inc., an Ohio corporation (“Lessee”).`)
       }
     );
   });
+
+  describe("Annotations", function () {
+    it("should extract the text under some annotations", async function () {
+      const loadingTask = getDocument(buildGetDocumentParams("bug1885505.pdf"));
+      const pdfDoc = await loadingTask.promise;
+
+      const page1 = await pdfDoc.getPage(1);
+      const annots = await page1.getAnnotations();
+      let annot = annots.find(x => x.id === "56R");
+      expect(annot.overlaidText).toEqual("Languages");
+
+      annot = annots.find(x => x.id === "52R");
+      expect(annot.overlaidText)
+        .toEqual(`Dynamic languages such as JavaScript are more difficult to com-
+pile than statically typed ones. Since no concrete type information
+is available, traditional compilers`);
+
+      annot = annots.find(x => x.id === "54R");
+      expect(annot.overlaidText)
+        .toEqual(`typed ones. Since no concrete type information
+is available, traditional compilers need to emit generic code that can
+handle all possible type combinations at runtime. We present an al-
+ternative compilation technique for dynamically-`);
+
+      annot = annots.find(x => x.id === "58R");
+      expect(annot.overlaidText).toEqual("machine");
+
+      annot = annots.find(x => x.id === "60R");
+      expect(annot.overlaidText)
+        .toEqual(`paths through nested loops. We have implemented
+a dynamic compiler for JavaScript based on our`);
+
+      annot = annots.find(x => x.id === "65R");
+      expect(annot.overlaidText).toEqual("Experimentation,");
+
+      annot = annots.find(x => x.id === "63R");
+      expect(annot.overlaidText)
+        .toEqual(`languages such as JavaScript, Python, and Ruby, are pop-
+ular since they are expressive, accessible to non-experts, and make
+deployment as easy as distributing a source file. They are used for
+small scripts as well as for`);
+    });
+  });
 });

web/annotation_layer_builder.css

@@ -126,6 +126,16 @@
         display: none;
       }
     }
+
+    .overlaidText {
+      position: absolute;
+      top: 0;
+      left: 0;
+      width: 0;
+      height: 0;
+      display: inline-block;
+      overflow: hidden;
+    }
   }
 
   .textLayer.selecting ~ & section {