Using custom font in linux failed

[yinghao-xue]

    page.insert_font(fontfile="font\\simsun.ttf", fontname="simsun")
    rc = page.insert_textbox(
        rect = rect,
        buffer = text,
        fontsize = fontsize,
        fontname="simsun",
        #fontfile="font\\simsun.ttf",
        color = color
    )

We are using this code to try inserting text with a custom font. It works correctly on Windows, but on Linux it throws the error: "Exception: need font file or buffer", and the custom font is not applied successfully—all Chinese characters are displayed as "?". We have tried directly using fontfile in insert_textbox, and we have already ruled out version and environment differences, but still no success.
The reason for using a custom font is that when inserting mixed Chinese and English text, built-in fonts such as "china-s" stretch half-width digits and letters to the same width as full-width characters, which does not meet our requirements—so we switched to a custom font. If this issue can be resolved, that would also be acceptable.

[JorjMcKie]

Have you confirmed that simsun.ttf actually exists on your Linux system? The backslash in any case cannot be used on a Linux system ...

You can always use the built-in CJK font. It supports Latin, Chinese, Korean and Japanese.
Try this:

cjk = pymupdf.Font("cjk")
fontname = "mycjk"

# then for each page where you need it:
page.insert_font(fontname=fontname, fontbuffer=cjk.buffer)

# text insertions do this:
page.insert_text(..., fontname=fontname, ...)
...

This ensures that a full blown font is used with a large range of languages.

[yinghao-xue]

It actually exists and can be used on Linux...
But your code works, THANK YOU !

[JorjMcKie]

If you have a local / your own font: all the better. Do not forget to do doc.subset_fonts() right before save. Then use positive garbage options.
This will shrink down the font to actually used Unicodes. Especially for the typically very large Asian fonts a real size saver.