Poor performance on a pdf document

[Lex-2008]

This PDF document:
http://lex-2008.github.io/pdf.js/print.pdf
has poor performance when scrolling.

as @chriskr noticed, this is probably related to text layer. Setting

.textLayer {display: none;}

increases performance.

To reproduce the issue:

1. Open attached document
2. Scroll it to the bottom
   Pass if scrolling performance is acceptable.

The file in question is a pdf printout of a http://habrahabr.ru/post/160035/ page, sent to me by a friend. Not sure how it was generated.

[Snuffleupagus]

@Lex-2008 For your information, appending textLayer=off to the URL is an even easier way to disable the textLayer completely, see: https://github.com/mozilla/pdf.js/wiki/Debugging-pdf.js#url-parameters.

[timvandermeij]

Scrolling is acceptable to good for this PDF now. Closing as resolved by #5586 and #5595.

[yurydelendik]

#6590 landed but it did not take in account that set text matrix operation can be used for individual glyphs. I think we can do better by applying the same logic as we used for translate operation in #6590.

P.S. delta calculated to make optimization work, four first components of transform matrix must be equal to previous value.

[nikhilshagri]

I would like to work on this bug. Can you give me some guidance/pointers for fixing this?

[Snuffleupagus]

#6590 landed but it did not take in account that set text matrix operation can be used for individual glyphs. I think we can do better by applying the same logic as we used for translate operation in #6590.

@yurydelendik Is this approximately what you had in mind: master...Snuffleupagus:combine-setTextMatrix? If so, I'll add a test-case and submit a PR.