Uneven clipping of blurs for circular objects

[Brodie Tucker]

Inkscape 0.48.1
Windows xp service pack 3

I start with a circle, the size is irrelevant. I then duplicate said object(or path) and remove fill, then apply a stroke. Apply a blur to that. Then duplicate the original object and select the newly duplicated piece as well as the stroke with blur, making sure the stroke is below, then set a clipping path. Now I have tested this with all sorts of different objects and such and it is only apparent as far as I can tell on anything that is from a circle to a full square, irregular shapes do not have this problem nor do full unaltered sqaures. The problem being that the blur is always slightly more 'focused' at each point of the compass. The very northern part, east point and so on. It is happening with both the circle object, the square object(with courner handle nodes modified) and the\ same thing when converted to paths. I have experimented with various different thing and always get the same result. I am able to circumnavigate this problem via a bit of tricky work with gradients but it is still a bug. But imo no overtly important :-). Cheers

[su_v (suv-lp)]

Could you attach sample SVG files explaining your problem visually, and possibly a screenshot how it looks in your Inkscape?

Do you compare rendering of the blurred and clipped objects in Inkscape, on-canvas, or is this about the exported bitmaps (PNG), other export formats or SVG renderers?

I can't detect an unevenness of the clipped blurred circle in a simple test following your initial description, screenshot attached).

[Brodie Tucker (bdt466)]

Well I have gotten this bug on the canvas but it is also prominent on exporting a .PNG file as well as .SVG. I have tried saving the file then re-opening and trying different methods but I have gotten the same result every time. I have also tried skirting around the stroke option by duplicating the circle, duplicating again, minimising this one(making smaller) and then Path>Difference. The following the same process but same result, I have also tried adding and deleting nodes thinking it may be strengthening at the node points but it seems this is not the case. Cheers

screenshot attached
(svg in comment below)

[Brodie Tucker (bdt466)]

Uh, I just looked at the svg file I uploaded, it seems it is fine for svg's but my Inkscape program is showing different as are the png exports

[su_v (suv-lp)]

Reproduced with Inkscape 0.48.1 and 0.48+devel r10145 on OS X 10.5.8 (i386) with default preferences.

You can avoid this effect by changing the preferences for 'Clippaths and masks' to
 [x] Put all clipped/masked objects into one group
and redo the clipping in your example. Or - if you don't want to change the default behavior of clips and masks - group the blurred path manually and then apply the clipping the group.

Possibly the underlying issue is related to the issue described in bug #562283 “Adding drop shadow to rotated object issue”, but I'm not sure, since preserved transforms or not doesn't make a difference in your example. AFAICT only grouping and clipping the group instead of the filtered object does.

[su_v (suv-lp)]

Oddly, in further tests, adding a stroke to the clip-path is another workaround to get an even rendering of the clipped blurred path in Inkscape (even though the stroke (or its width) should have no effect on the geometry of the clipped region).

[Beluga (buovjaga)]

Still confirmed with uneven-blur-clipping.svg

Win 7 64-bit
Inkscape 0.92pre1_64bit r15016