[Feature Request]: Clone pages

[samezyane]

Hi,

I have an SVG backgound image that repeats in many pages, what I have done so far is the following:

• create a PDF for the SVG background image 'pdfFromSvg.pdf' (using inkscape)
• create the final pdf document 'pdfDoc'
  const pdfDoc = await PDFDocument.create()
• load the 'pdfFromSvg.pdf' in a temporary PDFDocument
  const imgPdfDoc = await PDFDocument.load(base64of('pdfFromSvg.pdf'))
• loop through my loop and call:
  const [imgPage] = await pdfDoc.copyPages(imgPdfDoc, [0])
const pdfPage = pdfDoc.insertPage(idx, imgPage)
do the specific rendering on the newly inserted 'pdfPage'

I think that there is room to enhance the performance if there is a 'copyPage' version of 'copyPages' that copy a single page from a source pdf and that returns multiple instances of the same page,

• the code will be:
  const pdfDoc = await PDFDocument.create()
const imgPdfDoc = await PDFDocument.load(base64of('pdfFromSvg.pdf'))
const imgPages = await pdfDoc.copyPage(imgPdfDoc, 0, N) // copy the first page and return an array of N pages
• loop through my loop and call:
  const pdfPage = pdfDoc.insertPage(idx, imgPages[idx])
do the specific rendering on the newly inserted 'pdfPage'

By inserting the same page, my tests show that for a backround image that repeats 70 times:

• the processing time improves from 3 minutes to 10 seconds
• and the size of the pdf decreases from 18 MB to 1MB

Regards,

Saeed

[Hopding]

Hello @samezyane!

I think the best way to solve this problem would be to support cloning/copying PDFPage objects. And I certainly agree that this would be a useful feature to provide.

Until this feature lands in pdf-lib, I've created a workaround you can use in #47 (comment). Please take a look at the full example, but here's the gist of it:

/* Copies a PDFPage object */
const copyPage = (originalPage) => { ... };

const pdfDoc = await PDFDocument.create();
const donorDoc = await PDFDocument.load(...);

const [page1] = await pdfDoc.copyPages(donorDoc, [0]);

const page2 = copyPage(page1);
const page3 = copyPage(page1);

pdfDoc.addPage(page1);
pdfDoc.addPage(page2);
pdfDoc.addPage(page3);

// Do page-specific rendering here...

I hope this helps. Please let me know if you have any additional questions!

[Hopding]

Added this to the roadmap for tracking: #998.

[mericaliyigit]

Library can really benefit from a hardcopy/clone functionality.
I hit a similar bug today while trying to write some text on to the pdf and got it spread over multiple copied pages.