Hi,
Thanks to Kompza and RichardF I think I've pretty much got my head wrapped
round how MapCSS works. With my inexperience in mind though, I believe I've
spotted a way to significantly clean up MapCSS 0.2.
One ugly thing that all renderers seem to do is to treat the layer tag on
geometry as being a special case. The usual interpretation seems to be to
treat each layer as a completely distinct map, and to composite the layers
together as a final stage at the end. The result is that unlike specifying the
z-index of an element, the casings are brought above the lower elements by
specifying a higher layer.
I'd like to propose a casing-z-index property as simple solution that stops
this needing to be treated as a special case. Instead, casing z-indices are
specified on the exact same scale as element z-indices.
A quick example of how this might work:
way
{
casing-z-index: eval(layer * 10); // We in general want the casing to be the
lowest thing for any given "layer"
z-index: eval(layer * 10 + 1); // And the ways drawn over the top of the
casings
}
way[highway]
{
z-index: eval(layer * 10 + 7); // We want highways to appear above everything
except...
}
way[highway=trunk]
{
casing-z-index: eval(layer * 10 + 8); // For trunk roads, we want to
highlight them, so we bring the casing up above the other roads
z-index: eval(layer * 10 + 9); // And more so, bring the road above the
casing.
}
The downside of this proposal is of course that it would break existing style
sheets, in that space must be left in the z-index scale to allow casings to
slot in.
The upside though is that renderers need not do anything special or magical
with the layer tag, simplifying code, and pushing more style into the
stylesheet.
This proposal does bring up at least some extra issues. For example, when does
a shield's border get drawn, does it introduce a need for a border-z-index
property? If anyone else can think of more, please do get stuck in.
Thanks
Tom 'Beelsebob' Davie
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