Convert the getOutputScale helper function into a OutputScale class

Given the previous patch in particular, this seems like an overall nicer format since it avoids duplicating the `scaled` getter in each instance.

web/pdf_page_view.js

@@ -40,7 +40,7 @@ import {
 import {
   approximateFraction,
   DEFAULT_SCALE,
-  getOutputScale,
+  OutputScale,
   RendererType,
   RenderingStates,
   roundToDivide,
@@ -806,7 +806,7 @@ class PDFPageView {
     }
 
     const ctx = canvas.getContext("2d", { alpha: false });
-    const outputScale = (this.outputScale = getOutputScale());
+    const outputScale = (this.outputScale = new OutputScale());
 
     if (this.useOnlyCssZoom) {
       const actualSizeViewport = viewport.clone({

web/pdf_thumbnail_view.js

@@ -19,7 +19,7 @@
 // eslint-disable-next-line max-len
 /** @typedef {import("./pdf_rendering_queue").PDFRenderingQueue} PDFRenderingQueue */
 
-import { getOutputScale, RenderingStates } from "./ui_utils.js";
+import { OutputScale, RenderingStates } from "./ui_utils.js";
 import { RenderingCancelledException } from "pdfjs-lib";
 
 const DRAW_UPSCALE_FACTOR = 2; // See comment in `PDFThumbnailView.draw` below.
@@ -233,7 +233,7 @@ class PDFThumbnailView {
       canvas.mozOpaque = true;
     }
     const ctx = canvas.getContext("2d", { alpha: false });
-    const outputScale = getOutputScale();
+    const outputScale = new OutputScale();
 
     canvas.width = (upscaleFactor * this.canvasWidth * outputScale.sx) | 0;
     canvas.height = (upscaleFactor * this.canvasHeight * outputScale.sy) | 0;

web/ui_utils.js

@@ -78,20 +78,29 @@ const SpreadMode = {
 const AutoPrintRegExp = /\bprint\s*\(/;
 
 /**
- * Returns scale factor for the canvas. It makes sense for the HiDPI displays.
+ * Scale factors for the canvas, necessary with HiDPI displays.
- * @returns {Object} The object with horizontal (sx) and vertical (sy) scales.
- *   The scaled property is false if scaling is not required, true otherwise.
  */
-function getOutputScale() {
+class OutputScale {
-  const pixelRatio = window.devicePixelRatio || 1;
+  constructor() {
-  return {
+    const pixelRatio = window.devicePixelRatio || 1;
-    sx: pixelRatio,
-    sy: pixelRatio,
 
-    get scaled() {
+    /**
-      return this.sx !== 1 || this.sy !== 1;
+     * @type {number} Horizontal scale.
-    },
+     */
-  };
+    this.sx = pixelRatio;
+
+    /**
+     * @type {number} Vertical scale.
+     */
+    this.sy = pixelRatio;
+  }
+
+  /**
+   * @type {boolean} Returns `true` when scaling is required, `false` otherwise.
+   */
+  get scaled() {
+    return this.sx !== 1 || this.sy !== 1;
+  }
 }
 
 /**
@@ -836,7 +845,6 @@ export {
   DEFAULT_SCALE_DELTA,
   DEFAULT_SCALE_VALUE,
   getActiveOrFocusedElement,
-  getOutputScale,
   getPageSizeInches,
   getVisibleElements,
   isPortraitOrientation,
@@ -849,6 +857,7 @@ export {
   noContextMenuHandler,
   normalizeWheelEventDelta,
   normalizeWheelEventDirection,
+  OutputScale,
   parseQueryString,
   PresentationModeState,
   ProgressBar,