894957 - Don't attempt to draw transparent text

Status: RESOLVED FIXED

(Core :: Graphics: Text, defect)

Description

[Markus Stange [:mstange]]

Attachment: patch

PDF.js creates a layer of transparent text on top of its canvas for selection and copying. During scrolling, sometimes the whole page is invalidated and all the text on it is "repainted". For pages with a lot of text, the gfxTextRun::Draw part of this repaint takes long enough to cause noticeable jank on its own.

Comment 1

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Hmm wait. Does this create a timing channel attack against link-visited, by using CSS rules that make text invisible if a link is visited? I think it might :-(.

Maybe we can block this at a higher level where we can check for that?

Comment 2

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Oh, no, it's not a problem, because we require that color changes due to visited rules don't change alpha values. Never mind.

Comment 3

[Markus Stange [:mstange]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/ba041d0f69b3

Comment 4

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/ba041d0f69b3