Slow rendering of PDF with time spent in genericComposeSMask

[mstange]

Attach PDF file here: d2_cheat_sheet.pdf

Configuration:

• Web browser and its version: Firefox Nightly 2024-03-25
• Operating system and its version: macOS
• PDF.js version: ?
• Is a browser extension: browser-native

Steps to reproduce the problem:

1. Load the PDF

What is the expected behavior? It should draw quickly.

What went wrong? It was slow.

Profile: https://share.firefox.dev/49axVfO

---

The profile shows that all the time is spent waiting for readback in getImageData for genericComposeSMask.
What does genericComposeSMask do? Which APIs would be needed in canvas to allow implementing it on the GPU?

[marco-c]

This is probably the same as https://bugzilla.mozilla.org/show_bug.cgi?id=1874013.

[marco-c]

See also #14982 (comment).

[Snuffleupagus]

Duplicate of e.g. issue #17779?

[marco-c]

Yes!

It seems to be frequent enough that we should prioritize it soon.