852100 - SVG filters may shift and blur elements in embedded image

Status: RESOLVED DUPLICATE of bug 608812

(Core :: SVG, defect)

Description

[Branimir Lambov]

Attachment: firefox-filter.html

User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:19.0) Gecko/20100101 Firefox/19.0
Build ID: 20130307122903

Steps to reproduce:

The attached file contains an embedded SVG element that's not aligned on a pixel boundary. The embedded SVG contains two rectangles, one of which is under a filter that does nothing.


Actual results:

The two rectangles look different: the one under the filter is blurry, and its text is not as readable.


Expected results:

The two rectangles should look the same.

Comment 1

[Branimir Lambov]

We're seeing this in many Flash ad conversions, where blur being removed or a shadow being added at the end of a transition results in a visible wobble of portions of the image.

Comment 2

[Alice0775 White]

I can confirm the problem of comment#0 .

http://hg.mozilla.org/mozilla-central/rev/b03bb3ce8cee
Mozilla/5.0 (Windows NT 6.1; WOW64; rv:22.0) Gecko/20130318 Firefox/22.0 ID:20130318030947

And the problem existed since Firefox4...

Comment 3

[Robert Longson [:longsonr]]

From the SVG specification...

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

When applying this filter, the destination location may be offset by a fraction of a pixel in device space. In this case a high quality viewer should make use of appropriate interpolation techniques, for example bilinear or bicubic

Which is pretty much what we do. Makes it fuzzy for you though.

You should be able to modify filterRes to get a result which works better for your use cases.

Comment 4

[Branimir Lambov]

Attachment: Empty feComponentTransfer

This is not feOffset-specific. Any filter will cause it.

I believe the reason is that the buffer created for the image source is snapped to pixel boundaries relative to the SVG origin, while that should have been done relative to the origin of the page.

Comment 6

[u459114]

nsFilterInstance::ComputeNeededBoxes()
This function compute region in device units. 0.5 offset for drawing stoke is truncated.

We can not fix it unless FilterPrimitiveDescription carries filter subregion in user space(floating unit).

Comment 7

[u459114]

Attachment: hacking

Comment 8

[u459114]

Attachment: Bug 852100 - Part 1. Bring in pixel snap offset while painting source image.

Review commit: https://reviewboard.mozilla.org/r/168734/diff/#index_header
See other reviews: https://reviewboard.mozilla.org/r/168734/

Comment 10

[u459114]

Attachment: Bug 852100 - Part 2. A test case for varifying pixel snap with svg filter.

Review commit: https://reviewboard.mozilla.org/r/168762/diff/#index_header
See other reviews: https://reviewboard.mozilla.org/r/168762/

Comment 11

[u459114]

Comment on attachment 8897419 [details]
Bug 852100 - Part 1. Bring in pixel snap offset while painting source image.

Review request updated; see interdiff: https://reviewboard.mozilla.org/r/168734/diff/1-2/

Comment 12

[u459114]

Comment on attachment 8897462 [details]
Bug 852100 - Part 2. A test case for varifying pixel snap with svg filter.

Review request updated; see interdiff: https://reviewboard.mozilla.org/r/168762/diff/1-2/