1749563 - Some chars are rendered incorrectly in some documents

Status: VERIFIED FIXED

(Firefox :: PDF Viewer, defect, P1)

Description

[Michel Le Bihan]

Attachment: plakaty_informacyjne_hasla_a4.pdf

Hello,
I noticed that the PDF Viewer renders some chars in some documents incorrectly. Please see the attached screenshots. The : in the URL in the footer is rendered differently in Firefox PDF Viewer than in Evince.

Document source: https://cert.pl/uploads/2022/01/hasla/resources/plakaty_informacyjne_hasla_a4.pdf

Comment 1

[Michel Le Bihan]

Attachment: Firefox.png

Comment 2

[Michel Le Bihan]

Attachment: Evince.png

Comment 3

[Jonas Jenwald [:Snuffleupagus]]

This isn't the "normal" kind of font conversion bug, since it's connected to the specific text rendering mode being used (in this case 7); please see https://www.adobe.com/content/dam/acom/en/devnet/pdf/pdfs/PDF32000_2008.pdf#G8.1772271

Hence the bug would, most likely, be found in https://github.com/mozilla/pdf.js/blob/master/src/core/font_renderer.js

Comment 4

[Calixte Denizet (:calixte)]

:Snuffleupagus, thanks for the tip :).

So I looked in font_renderer.js what could be wrong and I think I found.
The : is a composite glyph (two .) and there is something wrong here:
https://github.com/mozilla/pdf.js/blob/236c8d47864e8ebf593bae21576670b59a7d4988/src/core/font_renderer.js#L202
If I understand correctly, if flags & 0x01 then we get two int16 else we get two uint8.

But according to the specs:
https://docs.microsoft.com/en-us/typography/opentype/spec/glyf
if flags & 0x02 (i.e. ARGS_ARE_XY_VALUES) then these two numbers must be treated as signed.

So I just handled the uint8 => int8 case and it works.
I think we could fix this TODO too:
https://github.com/mozilla/pdf.js/blob/236c8d47864e8ebf593bae21576670b59a7d4988/src/core/font_renderer.js#L214

:Snuffleupagus, if you began to work on a fix, feel free to take the bug.

Comment 5

[GitHub Bugzilla PR Linker]

Attachment: Link to GitHub pull-request: https://github.com/mozilla/pdf.js/pull/14456

Comment 6

[GitHub Bugzilla PR Linker]

Attachment: Link to GitHub master push: https://github.com/mozilla/pdf.js/commit/b0231cc88757cbef371fdac89864a609a568b819

Commit merged into master by GitHub
Authored by calixteman (calixteman)

Comment 7

[Virgil Sangerean]

Reproduced with 2022-01-11-09-38-27 build of Nightly.

Issue is no longer reproducible on 98.0b8 beta if Firefox.