The MyPaint team are doing great work, making progress towards MyPaint 1.2, I encourage you to give it a try, build it from source or check out the nightly builds. (Recent windows build Note: the filename mypaint-1.1.1a.7z may stay the same but the date of build does change.)
The Vector Layers feature in MyPaint is particularly interesting. One downside though is that the resulting OpenRaster files with vector layers are incompatible with most existing programs. MyPaint 1.0 was one of the few programs that managed to open the file at all, presenting an error message only for the layer it was not able to import. The other programs I tested, failed to import the file at all. It would be great if OpenRaster could be extended to include vector layers and more features but it will take some careful thought and planning.
It can be challenging enough to create a new and useful feature, planning ahead or trying to keep backwards compatibility makes matters even more complicated. With that in mind I wanted to add some support for vectors to the OpenRaster plugin. Similar to my previous work to round-trip metadata in OpenRaster I found a way to round-trip Paths/Vectors that is "good enough" and that I hope will benefit users. The GNU Image Manipulation Program already allows paths to be exported in Scalable Vector Graphics (SVG) format. All paths are exported to a single file,
paths.svgand are imported back from that same file. It is not ideal, but it is simple and it works.
Users can get the updated plugin immediately from the OpenRaster plugin gitorious project page. There is lots more that could be done behind the scenes, but for ordinary users I do not expect any changes as noticeable as these for a while.
Back to the code. I considered (and implemented) a more complicated approach that included changes to
stack.xml, where raster layers were stored as one group, and
paths (vectors layers) as another group. This approach was better for exporting information that was compatible with MyPaint but as previously mentioned, the files were not compatible with any other existing programs.
To ensure OpenRaster files that are back compatibility it might be better to always include a PNG file as the source for every layer, and to find another way to link to other types of content, such as text or vectors, or at some distant point in the future even video. A more complicated fallback system might be useful in the long run. For example the EPUB format reuses the Open Packaging Framework (OPF) standard, any pages can be stored in multiple formats, so long as it includes a fallback to another format, ending with a fallback to a few standard baseline formats (i.e. XHTML). The OpenRaster standard has an elegant simplicity, but there is so much more it could do.