Perfectly horizontal or vertical lines don't render to svg

[amauboussin]

Perfectly horizontal or vertical lines do not show up in svgs on my machine. Could be an issue with my specific setup, I am curious if anyone else can reproduce the issue.

Here is the code that causes the bug for me:

import pylab as plt
plt.plot([-1,1],[1,1]) #perfectly horizontal line does not render
plt.savefig('/Users/Andrew/Desktop/plot.svg', format='svg')

Here is a workaround I found:

import pylab as plt
plt.plot([-1,1],[1,1.001]) #not a perfectly horizontal line; renders
plt.savefig('/Users/Andrew/Desktop/plot.svg', format='svg')

My environment:
Matplotlib 1.10 on Mac OS X 10.7 obtained from Enthought

[pelson]

I get the same behaviour when viewing the svg produced in Safari on master. To help diagnosis, how are you viewing the produced SVG?

[amauboussin]

I also viewed the SVG in Safari when I found the issue.
However, I just tried Inkscape and found the same line that does not render in Safari renders in Inkscape. So maybe it is a bug in safari?

[amauboussin]

Another interesting thing to note: for the project I am doing I need to use zorder to put some things on top of others. When I export to svg and view in safari, the z order does not appear to have been followed and the wrong things are on top.When I export to png or view in Inkscape everything is in the right layer.

[WeatherGod]

Most likely a bug in safari (a snapping issue, maybe?). I can view your example just fine in Firefox. Just curious, would setting a larger linewidth for the line make a difference in safari?

[mdboom]

Probably a bug in WebKit, as it happens in Chrome, too:

http://code.google.com/p/chromium/issues/detail?id=135321

[pelson]

This is a problem upstream and there is no action for mpl as far as I can see. Should we document this somewhere? I've labelled it "doc", but if there is nothing to be done, we can close.

@amauboussin: Thanks for raising this, it is well worth knowing about!

[mdboom]

Chrome 33 no longer seems to have this bug.

Safari 7 does.

[pelson]

Closing - there is nothing for us to do here but wait for browsers to fix their bug.

[williamstein]

For what it is worth, I have different users (of SageMathCloud) who hit this bug constantly and report it to me. If any matplotlib experts had an idea for a workaround (even something horrible and crappy like slightly peturb the line), I would be interested... Even adding a link in this thread about how to complain to apple about this would be nice (?).

[slel]

One way to report bugs to Apple is to join their beta-tester program [1] and to test development versions of OS X. You get a "Feedback Assistant" app which lets you report bugs.

Last year I beta-tested OS X 10.10 Yosemite and I reported the Safari svg bug (horizontal and vertical lines not rendered) via the Feedback Assistant but that did not result in any fix.

I just re-enrolled to the beta-tester program for OS X 10.11 El Capitan and I'll report the bug again.

I created a page to display the bug [2]. Feel free to link to that page. Comments welcome.

[1] https://beta.apple.com/
[2] http://samuel.lelievre.free.fr/bug/safari-svg-bug-horizontal-vertical-line.html

[mdboom]

@slel: Thanks.

As for workarounds: @williamstein's suggestion to slightly perturb the line is interesting. I suppose we should experiment with how much skew would be required and how badly that looks. The downside, of course, is that degrades the plot for everyone. (Unfortunately, I don't have access to a Mac this week to play -- anyone else is welcome to.)

We could attach a small amount of Javascript to the SVG that detects the browser and displays a warning (and a suggestion to switch to Chrome or Firefox) if it's one of the known broken browsers...

[slel]

The bug is fixed in WebKit. And thus in Safari 9.
This is confirmed by beta-testers of WebKit, of iOS 9, and of OS X 10.11 El Capitan.

[tacaswell]

I am strongly 👎 on adding skew to work around bugs in external libraries.

Does this issue depend on line width?