[api-minor] Add a new getXfaPageViewport helper function to support printing

This patch provides an overall simpler *and* more consistent way of handling the `viewport` parameter during printing of XFA forms, since it's now again guaranteed to always be an instance of `PageViewport`.
Furthermore, for anyone attempting to e.g. implement custom printing of XFA forms this probably cannot hurt either.

src/display/api.js

@@ -743,8 +743,10 @@ class PDFDocumentProxy {
   }
 
   /**
+   * NOTE: This is (mostly) intended to support printing of XFA forms.
+   *
    * @type {Object | null} An object representing a HTML tree structure
-   * to render the XFA, or `null` when no XFA form exists.
+   *   to render the XFA, or `null` when no XFA form exists.
    */
   get allXfaHtml() {
     return this._transport._htmlForXfa;

src/display/display_utils.js

@@ -606,6 +606,20 @@ class PDFDateString {
   }
 }
 
+/**
+ * NOTE: This is (mostly) intended to support printing of XFA forms.
+ */
+function getXfaPageViewport(xfaPage, { scale = 1, rotation = 0 }) {
+  const { width, height } = xfaPage.attributes.style;
+  const viewBox = [0, 0, parseInt(width), parseInt(height)];
+
+  return new PageViewport({
+    viewBox,
+    scale,
+    rotation,
+  });
+}
+
 export {
   addLinkAttributes,
   DEFAULT_LINK_REL,
@@ -616,6 +630,7 @@ export {
   DOMSVGFactory,
   getFilenameFromUrl,
   getPdfFilenameFromUrl,
+  getXfaPageViewport,
   isDataScheme,
   isPdfFile,
   isValidFetchUrl,

src/display/xfa_layer.js

@@ -13,8 +13,6 @@
  * limitations under the License.
  */
 
-import { PageViewport } from "./display_utils.js";
-
 class XfaLayer {
   static setupStorage(html, fieldId, element, storage, intent) {
     const storedData = storage.getValue(fieldId, { value: null });
@@ -134,13 +132,8 @@ class XfaLayer {
 
     const rootDiv = parameters.div;
     rootDiv.appendChild(rootHtml);
-
-    let { viewport } = parameters;
-    if (!(viewport instanceof PageViewport)) {
-      viewport = new PageViewport(viewport);
-    }
-    const coeffs = viewport.transform.join(",");
-    rootDiv.style.transform = `matrix(${coeffs})`;
+    const transform = `matrix(${parameters.viewport.transform.join(",")})`;
+    rootDiv.style.transform = transform;
 
     // Set defaults.
     rootDiv.setAttribute("class", "xfaLayer xfaFont");

src/pdf.js

@@ -18,6 +18,7 @@ import {
   addLinkAttributes,
   getFilenameFromUrl,
   getPdfFilenameFromUrl,
+  getXfaPageViewport,
   isPdfFile,
   isValidFetchUrl,
   LinkTarget,
@@ -108,6 +109,7 @@ export {
   loadScript,
   PDFDateString,
   RenderingCancelledException,
+  getXfaPageViewport,
   // From "./display/api.js":
   build,
   getDocument,