Scale page content

src/api/PDFPage.ts

@@ -13,6 +13,7 @@ import {
   pushGraphicsState,
   translate,
   LineCapStyle,
+  scale,
 } from 'src/api/operators';
 import PDFDocument from 'src/api/PDFDocument';
 import PDFEmbeddedPage from 'src/api/PDFEmbeddedPage';
@@ -39,6 +40,10 @@ import {
   PDFOperator,
   PDFPageLeaf,
   PDFRef,
+  PDFNumber,
+  PDFDict,
+  PDFArray,
+  PDFObject,
 } from 'src/core';
 import {
   addRandomSuffix,
@@ -566,6 +571,73 @@ export default class PDFPage {
     this.node.wrapContentStreams(startRef, endRef);
   }
 
+  /**
+   * Scale the content of a page. This is useful after resizing an exisiting page.
+   * This scales only the content not the annots. See also: [[scaleAnnots]]
+   * ```js
+   * // bisect the size of the page
+   * p.setSize(p.getWidth() / 2, p.getHeight() / 2);
+   *
+   * // scale the content of the page down by 50% in x and y
+   * page.scaleContent(0.5, 0.5);
+   * ```
+   * @param x The factor by wich the x-axis for the content should be scaled (e.g. 0.5 is 50%)
+   * @param y The factor by wich the y-axis for the content should be scaled (e.g. 0.5 is 50%)
+   */
+  scaleContent(x: number, y: number): void {
+    assertIs(x, 'x', ['number']);
+    assertIs(y, 'y', ['number']);
+
+    this.node.normalize();
+    this.getContentStream();
+
+    const start = this.createContentStream(pushGraphicsState(), scale(x, y));
+    const startRef = this.doc.context.register(start);
+
+    const end = this.createContentStream(popGraphicsState());
+    const endRef = this.doc.context.register(end);
+
+    this.node.wrapContentStreams(startRef, endRef);
+  }
+
+  /**
+   * Scale the annots of a page. This is useful if you want to scale a page with comments or other annots.
+   * ```JS
+   * // scale the content of the page down by 50% in x and y
+   * page.scaleContent(0.5, 0.5);
+   *
+   * // scale the content of the page down by 50% in x and y
+   * page.scaleAnnots(0.5, 0.5);
+   * ```
+   * See alos: [[scaleContent]]
+   * @param x The factor by wich the x-axis for the annots should be scaled (e.g. 0.5 is 50%)
+   * @param y The factor by wich the y-axis for the annots should be scaled (e.g. 0.5 is 50%)
+   */
+  scaleAnnots(x: number, y: number) {
+    const annots = this.node.Annots();
+
+    // loop annotations
+    annots?.asArray().forEach((ref: PDFObject) => {
+      const i = annots.indexOf(ref);
+
+      if (i === undefined) return;
+
+      const annot = annots.lookup(i, PDFDict);
+
+      if (!annot) return;
+
+      ['RD', 'CL', 'Vertices', 'QuadPoints', 'L', 'Rect'].forEach((el) => {
+        const list = annot.get(PDFName.of(el)) as PDFArray;
+        if (list) this.scalePDFNumbers(list, x, y);
+      });
+
+      const pdfNameInkList = annot.get(PDFName.of('InkList')) as PDFArray;
+      pdfNameInkList
+        ?.asArray()
+        .forEach((arr) => this.scalePDFNumbers(arr as PDFArray, x, y));
+    });
+  }
+
   /**
    * Reset the x and y coordinates of this page to `(0, 0)`. This operation is
    * often useful after calling [[translateContent]]. For example:
@@ -1500,4 +1572,13 @@ export default class PDFPage {
 
     return key;
   }
+
+  private scalePDFNumbers(arr: PDFArray, x: number, y: number): void {
+    arr?.asArray().forEach((el, i) => {
+      if (el instanceof PDFNumber) {
+        const factor = i % 2 === 0 ? x : y;
+        arr.set(i, PDFNumber.of(el.asNumber() * factor));
+      }
+    });
+  }
 }