[api-minor] Re-factor the basic textLayer-functionality

This is very old code, and predates e.g. the introduction of JavaScript classes, which creates unnecessarily unwieldy code in the viewer.
By introducing a new `TextLayer` class in the API, similar to how e.g. the `AnnotationLayer` looks, we're able to keep most parameters on the class-instance itself. This removes the need to manually track them in the viewer, and simplifies the call-sites.

This also removes the `numTextDivs` parameter from the "textlayerrendered" event, since that's only added to support default-viewer functionality that no longer exists.

Finally we try, as far as possible, to polyfill the old `renderTextLayer` and `updateTextLayer` functions since they are exposed in the library API.
For *simple* invocations of `renderTextLayer` the behaviour should thus be the same, with only a warning printed in the console.

test/driver.js

@@ -22,8 +22,8 @@ const {
   GlobalWorkerOptions,
   Outliner,
   PixelsPerInch,
-  renderTextLayer,
   shadow,
+  TextLayer,
   XfaLayer,
 } = pdfjsLib;
 const { GenericL10n, parseQueryString, SimpleLinkService } = pdfjsViewer;
@@ -297,13 +297,12 @@ class Rasterize {
         `:root { --scale-factor: ${viewport.scale} }`;
 
       // Rendering text layer as HTML.
-      const task = renderTextLayer({
+      const textLayer = new TextLayer({
         textContentSource: textContent,
         container: div,
         viewport,
       });
-
-      await task.promise;
+      await textLayer.render();
 
       svg.append(foreignObject);
 
@@ -327,15 +326,14 @@ class Rasterize {
         `:root { --scale-factor: ${viewport.scale} }`;
 
       // Rendering text layer as HTML.
-      const task = renderTextLayer({
+      const textLayer = new TextLayer({
         textContentSource: textContent,
         container: dummyParent,
         viewport,
       });
+      await textLayer.render();
 
-      await task.promise;
-
-      const { _pageWidth, _pageHeight, _textDivs } = task;
+      const { pageWidth, pageHeight, textDivs } = textLayer;
       const boxes = [];
       let j = 0,
         posRegex;
@@ -343,7 +341,7 @@ class Rasterize {
         if (type) {
           continue;
         }
-        const { top, left } = _textDivs[j++].style;
+        const { top, left } = textDivs[j++].style;
         let x = parseFloat(left) / 100;
         let y = parseFloat(top) / 100;
         if (isNaN(x)) {
@@ -352,12 +350,12 @@ class Rasterize {
           // string, e.g. `calc(var(--scale-factor)*66.32px)`.
           let match = left.match(posRegex);
           if (match) {
-            x = parseFloat(match[1]) / _pageWidth;
+            x = parseFloat(match[1]) / pageWidth;
           }
 
           match = top.match(posRegex);
           if (match) {
-            y = parseFloat(match[1]) / _pageHeight;
+            y = parseFloat(match[1]) / pageHeight;
           }
         }
         if (width === 0 || height === 0) {
@@ -366,8 +364,8 @@ class Rasterize {
         boxes.push({
           x,
           y,
-          width: width / _pageWidth,
-          height: height / _pageHeight,
+          width: width / pageWidth,
+          height: height / pageHeight,
         });
       }
       // We set the borderWidth to 0.001 to slighly increase the size of the

test/unit/pdf_spec.js

@@ -57,6 +57,7 @@ import {
 } from "../../src/display/display_utils.js";
 import {
   renderTextLayer,
+  TextLayer,
   updateTextLayer,
 } from "../../src/display/text_layer.js";
 import { AnnotationEditorLayer } from "../../src/display/editor/annotation_editor_layer.js";
@@ -108,6 +109,7 @@ const expectedAPI = Object.freeze({
   renderTextLayer,
   setLayerDimensions,
   shadow,
+  TextLayer,
   UnexpectedResponseException,
   updateTextLayer,
   Util,

test/unit/text_layer_spec.js

@@ -13,13 +13,10 @@
  * limitations under the License.
  */
 
-import {
-  renderTextLayer,
-  TextLayerRenderTask,
-} from "../../src/display/text_layer.js";
 import { buildGetDocumentParams } from "./test_utils.js";
 import { getDocument } from "../../src/display/api.js";
 import { isNodeJS } from "../../src/shared/util.js";
+import { TextLayer } from "../../src/display/text_layer.js";
 
 describe("textLayer", function () {
   it("creates textLayer from ReadableStream", async function () {
@@ -30,18 +27,14 @@ describe("textLayer", function () {
     const pdfDocument = await loadingTask.promise;
     const page = await pdfDocument.getPage(1);
 
-    const textContentItemsStr = [];
-
-    const textLayerRenderTask = renderTextLayer({
+    const textLayer = new TextLayer({
       textContentSource: page.streamTextContent(),
       container: document.createElement("div"),
       viewport: page.getViewport({ scale: 1 }),
-      textContentItemsStr,
     });
-    expect(textLayerRenderTask instanceof TextLayerRenderTask).toEqual(true);
+    await textLayer.render();
 
-    await textLayerRenderTask.promise;
-    expect(textContentItemsStr).toEqual([
+    expect(textLayer.textContentItemsStr).toEqual([
       "Table Of Content",
       "",
       "Chapter 1",
@@ -70,18 +63,14 @@ describe("textLayer", function () {
     const pdfDocument = await loadingTask.promise;
     const page = await pdfDocument.getPage(1);
 
-    const textContentItemsStr = [];
-
-    const textLayerRenderTask = renderTextLayer({
+    const textLayer = new TextLayer({
       textContentSource: await page.getTextContent(),
       container: document.createElement("div"),
       viewport: page.getViewport({ scale: 1 }),
-      textContentItemsStr,
     });
-    expect(textLayerRenderTask instanceof TextLayerRenderTask).toEqual(true);
+    await textLayer.render();
 
-    await textLayerRenderTask.promise;
-    expect(textContentItemsStr).toEqual([
+    expect(textLayer.textContentItemsStr).toEqual([
       "Table Of Content",
       "",
       "Chapter 1",