345048 - Scrolling with spellchecked words visible is slower

Status: RESOLVED FIXED

(Core :: Spelling checker, defect)

Description

[Brett Wilson]

Scrolling a large textarea quickly with the scroll thumb seems to be slower with misspelled words are visible.

Open a large textarea, for example, go here:
  https://bugzilla.mozilla.org/attachment.cgi?id=227870&action=edit
and click "edit attachment as comment," or:
  http://en.wikipedia.org/w/index.php?title=Jimi_Hendrix&action=edit
The first part of the text will have a lot of misspellings, but the rest won't because we've hit the maximum number of misspellings.

Scroll quickly with the thumb. At the top where there are misspellings, scrolling is slower. At the bottom, it is faster. Turning off spellchecking for the field makes it all fast.

Comment 1

[Ria Klaassen (not reading all bugmail)]

Everything happens slower in the box. When you right-click on a marked word, the context-menu appears slower, when you click on an item, the menu disappears slower.

Comment 2

[Boris Zbarsky [:bzbarsky]]

Attachment: Zipped-up profile; use jar: URI to browse.

Salient points:

Total hit count: 132794
Count %Total  Function Name
29376   22.1     nsAttrAndChildArray::IndexOfChild(nsINode*) const
14684   11.1     _end
8722   6.6     nsVoidArray::InsertElementAt(void*, int)
5514   4.2     nsRange::IsIncreasing(nsIDOMNode*, int, nsIDOMNode*, int)

Of the 132794 hits, 112081 are under nsTextFrame::PaintUnicodeText.  This breaks up as:

  112081 nsTextFrame::PaintUnicodeText(nsPresContext*, nsIRenderingContext&,
                                       nsStyleContext*, nsTextPaintStyle&, int, 
                                       int)
      67522 nsFrameSelection::LookUpSelection(nsIContent*, int, int, int)
      29867 nsRenderingContextImpl::DrawString(unsigned short const*,
                                               unsigned int, int, int, int,
                                               int const*)
       7385 nsTextFrame::PaintTextDecorations(nsIRenderingContext&,
                                              nsStyleContext*, nsPresContext*,
                                              nsTextPaintStyle&, int, int, int, 
                                              unsigned short*,
                                              SelectionDetails*, unsigned int,
                                              unsigned int, int const*)
       4807 .L1149
       1348 nsTextFrame::PrepareUnicodeText(nsTextTransformer&,
                                            nsAutoIndexBuffer*,
                                            nsAutoTextBuffer*, int*, int, int*, 
                                            int)

LookupSelection spends all its time in our old friend nsRange::ComparePoints.

Comment 3

[Boris Zbarsky [:bzbarsky]]

So the basic problem, I think, is that for every text frame we do hundreds of range inclusion comparisons here.  There's just _got_ to be a better way of doing this.  One thing that comes to mind is sorting the selection ranges by end point (and start point?) and keeping a cached "last looked up range" thingie so that LookUpSelection starts looking at a reasonable spot and can quickly decide when to stop...

Comment 4

[Jonas Sicking (:sicking) No longer reading bugmail consistently]

So even with my IsIncreasing patch doing a ComparePoints is a non-trivial amout of work. So even if I would be able to double speed up ComparePoints (which i think is doable) it doesn't look like that'd be a significant win (30000 out of 130000 Hits).

Comment 5

[Boris Zbarsky [:bzbarsky]]

Well.  It's a 25% speedup in scrolling.  More importantly, its a 50% reduction in the difference between scrolling while spell-checking and just scrolling...

That assumes we don't make algorithmic changes to just reduce the number of calls to ComparePoints.  Like I said in comment 3, I think we should think about ways to make such changes.

Comment 6

[Brett Wilson]

Fixed by bug 345099.