Page.clip_to_rect() drops 'sh' (shading) operators

[BenVosper]

Description of the bug

We are noticing that Page.clip_to_rect() incorrectly deletes certain graphic elements, even if they fall within the clip box. I've had this for PDFs authored in Adobe Illustrator containing certain kinds of gradients on curved lines - which are expressed in the PDF as Shading elements. I've created a minimal PDF example below.

I don't know enough about the PDF spec internals to be able to debug any further, so let me know if I'm missing anything. clip_to_rect seems to perform perfectly in all other scenarios, it's just these types of graphics.

Thanks for your help!

How to reproduce the bug

Using the minimal PDF attached below, we can see that any clip_to_rect operation that does not include the origin of the page (top left) results in the gradient shading being deleted, even if the gradient is visually in the clipped area:

import pymupdf


def clipped_content(clip):
    doc = pymupdf.open("shading-repro.pdf")
    doc[0].clip_to_rect(clip)
    doc2 = pymupdf.open(stream=doc.tobytes(garbage=3, clean=True))
    return b"".join(doc2.xref_stream(x) for x in doc2[0].get_contents())


print("pymupdf", pymupdf.version)
for label, clip in [
    ("whole page                 ", pymupdf.Rect(0, 0, 400, 400)),
    ("right half (holds shading) ", pymupdf.Rect(200, 0, 400, 400)),
    ("page inset by 1pt          ", pymupdf.Rect(1, 1, 399, 399)),
    ("1x1 at PDF origin, no shading in it", pymupdf.Rect(0, 399, 1, 400)),
]:
    content = clipped_content(clip)
    print(f"  {label} -> sh kept: {b'sh' in content}   {content!r}")

This prints:

pymupdf ('1.28.2', '1.28.2', None)
  whole page                  -> sh kept: True
  right half (holds shading)  -> sh kept: False
  page inset by 1pt           -> sh kept: False
  1x1 at PDF origin, no shading in it -> sh kept: True

The final test also shows that the shading graphic is not deleted when clipping to the origin where the graphic is not present.

shading-repro.pdf

PyMuPDF version

1.28.2

Operating system

Linux

Python version

3.14