244975 - Deeply nested hierarchies are too slow (GetOwnerSVGElement, GetCTM & GetScreenCTM)

Status: RESOLVED WONTFIX

(Core :: SVG, defect)

Description

[Alex Fritze]

I did some profiling on adding an svg elements to deeply nested groups.
For my debug build I get 
(0.143 +/- 0.006) ms for adding a <circle> to a single <svg> element and
(3.103 +/- 0.090) ms for adding a <circle> to the innermost element in a tree of
1000 <g>'s.
In fact the time grows linearly with the nesting level.
The  most likely culprit is our implementation of GetOwnerSVGElement() which
gets called by most graphics elements when the parent chain changes (e.g. when
they get appended to other content). The current implementation of that method
just walks the parent chain until it encounters the owner svg element. 
I think we should change it so that for non-container elements it calls
GetOwnerSVGElement() on its parent and for container elements (<g>) it returns a
cached pointer.
The same goes for GetCTM and GetScreenCTM.

Comment 1

[Alex Fritze]

The situation is even worse on deleting. 
Deleting an <svg>-element scales quadratically with the number of nested
elements it contains :-(

Comment 2

[Boris Zbarsky [:bzbarsky]]

Is this a big problem in real life?  That is, do SVG trees commonly get this deep?

Comment 3

[Alex Fritze]

No, SVGs tend to be relatively shallow (depth<<10), so I don't think this is a
significant factor in practice.