Re: [matplotlib-devel] MEP26: Artist-level stylesheets

[R H. <rha...@gm...>]

On 20 July 2014 14:23, jamesramm <jam...@gm...> wrote:

> We cannot stick with the 'standard' CSS syntax by necessity, simply because
> the standard CSS selectors and properties are defined from HTML and do not
> match with matplotlib.
> I.E we want to select by artist type, which doesn't exist in HTML and use
> properties such as linewidth.
>

I'm not sure what it is about CSS syntax that isn't up to the job. For
example, SVG works with standard CSS syntax (see
http://www.w3.org/TR/SVG/styling.html#StylingWithCSS). Perhaps we just have
a different view of what constitutes CSS vs. HTML/SVG/whatever.

The example in the SVG spec is:

rect {
  fill: red;
  stroke: blue;
  stroke-width: 3
}


But if we define the element name for a Line2D instance as "line2d" then
CSS snippet could just become:

line2d {
  stroke: blue;
  stroke-width: 3
}


Sure, matplotlib doesn't define a genuine DOM, but I understand there is
interest in moving to a model more like that. In which case, perhaps a good
way to proceed in the meantime would be to have artists expose a DOM facade
suitable for styling. (Perhaps even using SVG element conventions?)

NB. matplotlib already uses pyparsing, so it would be pretty
straightforward to knock together a parser for CSS (or whatever subset is
needed). Or there are existing Python CSS parser libraries.



> Qt - Pyside/PyQt ('QSS')
> Mapnik ('CartoCSS')
> PyGal supports stylesheets (don't know much about this library)
>
>
If we don't use CSS then +1 for using some other standard.



> As I say, an alternative could be simply using the ConfigParser
>
>
> Richard Hattersley wrote
> >>
> >> Do you have ideas on how one or more stylesheets would be "attached" to
> a
> >> particular figure, etc?
> >>
> >> Regards,
> >> Richard Hattersley
> >>
>
>

> b) Filtering artists
> Another problem is that we would generally want to treat artists which are
> solely for the construction of the Axes differently to those artists that
> define a plot. I.E we might want to define Line2D as having the colour red,
> but we want lines which compose the Axes to be black or grey.
> My initial proposal is to develop stylesheets for artist primitives only.
> But eventually we will want to style artist containers aswell.
> The problem matplotlib has is that the properties for artist containers are
> not uniform/intuitive.
> It generally has a API where artists which are 'contained' by other artists
> are set by calling properties...e.g. axes.set_ylabel(text = , etc...)
>

The DOM facade could help bridge the gap. For example, a "DOM" instance
returned by an Axes object could pretend to have "text" element children.
Styling those would route the style information back to the underlying Axes
object. For example:


text {
  font-size: 12pt;
}

axes text.ylabel {
  font-size: 10pt;
}

I would imagine setting stylesheets through the axes or figure methods
> (axes.setStyleSheet() or figure.setStyleSheet()). Via figure would require
> being able to differentiate between different axes - i.e. introducing the
> 'container' level syntax I mentioned above.
>
> I would imagine that this would eventually replace rcparams to define the
> default style. I would also like to see the default look of graphs moving
> away from the very dated, 90's style MATLAB appearance!
>

That would be an excellent start. More complicated mechanisms can always be
added later if necessary.

Richard