861153 - feConvolveMatrix effect behaves inconsistently

Status: RESOLVED INVALID

(Core :: SVG, defect)

Description

[Mike Sierra]

Attachment: Firefox rendering

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:19.0) Gecko/20100101 Firefox/19.0
Build ID: 20130307023931

Steps to reproduce:

* Go to http://letmespellitoutforyou.com/samples/svg_inlineFilters.html
* Choose filter_convolve.svg#sharpenMore or filter_convolve.svg#moatMore


Actual results:

These effects rendered differently than in other web engines


Expected results:

Effect should apply the same formula, so pixel values should match.

Comment 1

[Mike Sierra]

Attachment: WebKit rendering

Comment 2

[Mike Sierra]

Attachment: Opera rendering of http://letmespellitoutforyou.com/samples/svg/filter_convolve.svg

Comment 3

[Mike Sierra]

View that SVG directly to test browsers that don't support CSS filter:url(filters.svg#filter)

Comment 4

[Robert Longson [:longsonr]]

From http://www.w3.org/TR/SVG/filters.html#feConvolveMatrixElement

Because they operate on pixels, matrix convolutions are inherently resolution-dependent. To make ‘feConvolveMatrix’ produce resolution-independent results, an explicit value should be provided for either the ‘filterRes’ attribute on the ‘filter’ element and/or attribute ‘kernelUnitLength’.

The viewBox scales the filter and there's no filterRes so that's why it's different because Opera tries to do something to mask the resolution dependence. Do take this up with the w3c SVG folks though via http://lists.w3.org/Archives/Public/www-svg/ if the specification were to state explicitly what should happen we'd likely follow it.

Comment 5

[Mike Sierra]

Thanks; I forwarded the issue on as you suggested.