Hi Friends,
I'm posting here because I think this MUST be me either not understanding something, or temporarily forgetting something. But it does smack of "bug"

It's very simple to reproduce:

• Draw 2 perfectly horizontal lines, using node x and y coordinates to make sure that y coordinates are identical. The 2 lines don't have to be next to each other. They can be anywhere on canvas, as long as each one is perfectly horizontal by y coordinates.
• Give them both a blur.

If this is reproducable on all systems, you should see NO blur, although the bounding boxes are enlarged to indicate a blur.
Now, select one node, and either change the y coordinate, or just drag it. Bam! There's the blur!
Weird, right?

I'm on Windows 7, 64-bit, with Inkscape 0.48 stable release.

Just on impulse, I thought to check if the same holds true for perfectly verticle lines. And yes! Follow the exact same steps, except use the x and y coordinates to make them perfectly vertical, ie - both x coordinates are identical for each line. Apply blur. Same result.

Here's the test file for you to examine:


Please tell me I've gone temporarily daft, and remind me why this happens

brynn wrote:posting here because I think this MUST be me either not understanding something, or temporarily forgetting something. But it does smack of "bug"

Others thought so too ("it's a bug!") - but as you can read in the comments of the relevant report, the error is rather that the blurred path is rendered at all in Inkscape and not that it is not blurred (due to the way filter effects work, following the SVG specification):

Bug #168943 in Inkscape: “Blurring a zero-height or zero-width path”

Well, it seems a little buggy but anyway here's a workaround if you really need it.
draw your line - exactly horizontal or vertical - stroke it with what you want. draw another object; I used lines, and one of those nifty ctrl-click-draw-a-circle points.
Give your unwanted other object (that you just drew) a stroke and fill of nothing. Group it with the line you want to blur.
Open your fill and stroke dialog, and blur away.

Here's an example.

I have to point out that if you ungroup the blurred line immediately loses its blur. If you then regroup you have to go back to the fill and stroke dialog to set the blur again because it has been automatically been reset to zero.

Another workaround that I've used in the past is to use Stroke To Path to convert your line into a filled path which will then blur as expected. Obviously this is not ideal if you want your path to remain a path, but might help in some situations.

Wow, this bug has been around since 2007??

~suv, could you explain in simpler language why this happens? I could not understand the technical discussion. It just seems weird that moving a node 0.10 off of horizontal/vertical will allow the blur to be rendered.

Also, I looked for the "this bug affects me too!" link, so I could just chime in, but it's not there. I looked at all the duplicate bugs, and none of them show that button. Should I just add a quick comment with test file attached?

Thanks for workarounds, druban and Xav. For me, I'm good with just moving a node by 0.10. But maybe your comments will help others.