Issues with 'ex' relative units for <svg> width, height

[Changhyun Kwon]

I have tried to convert this SVG file to PNG:
https://gist.github.com/chkwon/6ac383f4275720402027b3b7d4614ac1

using the command-line tool:

    inkscape -f e2293e769a19cf7cc131560e7d30a493cf399b8a.svg -e e2293e769a19cf7cc131560e7d30a493cf399b8a.png -h 40pt

Although there are some warnings, my Linux version can convert it successfully, while my Mac version cannot: it produces a blank PNG file. It produces the following message:

/Applications/Inkscape.app/Contents/Resources/bin/inkscape -f /Users/chkwon/test/test.svg -e /Users/chkwon/test/test.png

    ** (inkscape-bin:32096): WARNING **: SPIStyle::readIfUnset(): Invalid style property id: 90 value: static
    Background RRGGBBAA: ffffff00
    Area -1:-1:0:0 exported to 40 x 40 pixels (3600 dpi)
    Bitmap saved as: /Users/chkwon/test/test.png

In Linux, it instead says:

    Area 0:0:36634.4:2393.2 exported to 612 x 40 pixels (1.50426 dpi)

Both Mac and Linux has Inkscape 0.91 r13725. When I downgraded to Mac version 0.48.5 r10040, it works good.

[su_v (suv-lp)]

Not reproduced with Inkscape 0.91 r13725 on Ubuntu 14.04
Reproduced with Inkscape 0.91 r13725 (official package as well as with regular local build installed into fixed prefix), lp:inkscape 0.92.x r15116 (local build) on OS X 10.7.5.

The issue seems to be related to 'ex' units used for for the root <svg> element's width and height attributes:

<svg xmlns:xlink="http://www.w3.org/1999/xlink" width="85.087ex" height="5.558ex" focusable="false" xmlns="http://www.w3.org/2000/svg" style="vertical-align: -2.054ex; margin-bottom: -0.147ex; max-width: 736px; position: static;" viewBox="0 -1445.5 36634.4 2393.2">

“(...) the em and ex unit identifiers are relative to the current font's font-size and x-height, respectively.“

Also affects regular opening (via GUI), and import of the file into a new document - the issue is not specific to command line usage or PNG export.

Import into a new document applies this transformation to the imported group (with 0.91):
    matrix(0,0,0,0,375,532.3622)
which renders 'invisible' since the group is scaled to zero size.

[su_v (suv-lp)]

Testing with archived trunk builds (on OS X 10.7.5):
- not reproduced with lp:inkscape rev <= 13001,
- reproduced with lp:inkscape >= 13002;
the changes in r13002 seem to have contributed to the reported issue:

Revision 13002:
* Added new base class to handle viewBox and preserveAspectRatio.
* Updated sp-root, sp-symbol, sp-image, sp-pattern, marker to use new class.
* Fixed some viewport issues when % used.
https://bazaar.launchpad.net/~inkscape.dev/inkscape/trunk/revision/13002

Unclear to me at this point why the tested stable Linux build (package from inkscape PPA: 0.91.0+52~ubuntu14.04.1) produces a different result (?).

A more recent (local) trunk build on Ubuntu 14.04 (Inkscape 0.92+devel 15110 (Sep 4 2016)) however does reproduce the same problem as described in comment #1 - the content does not render visibly when opening the file in the GUI, nor when importing the file into a new (empty) document.

[su_v (suv-lp)]

Also reproduced on Ubuntu 14.04 with latest package from Inkscape Trunk PPA (1:0.91.0+devel+15174+77~ubuntu14.04.1).

[ivanistheone (ivan-savov)]

In case this helps with tracking down the issue, I've noticed that this type of SVG works with 0.91:

```
<svg style="width: 15ex; height: 5ex; vertical-align: -0.692ex; margin: 1px 0px;" viewBox="..."><g stroke="black" fill="black">...</g></svg>
```

But this fails:
```
<svg width="15ex" height="5ex" style="vertical-align: -0.692ex;" viewBox="..." role="img" focusable="false"><g stroke="currentColor" fill="currentColor" stroke-width="0">...</g></svg>
```

It seems Inkskape v0.91 has a problem the SVG that has `height` and `width` as attributes rather than as parts of the `style` attribute.