[Mapcss] multi-strokes and subparts

[Sebastian Klein]

Sebastian Spaeth wrote:
> Heureka! ceux does multi-strokes with subparts now
> 
> I had to try quite a lot of options and rewrite a bit of code, but it
>  seems to work fine now. Let me describe the strategy I chose:
> 
> 1) For each element, if there are only "generic" rules (without any 
> subparts specified), render that as one stroke/fill. So:
> 
> way [natural] {fill-opacity: 0.4;} way [natural] {fill-color:black;}
> 
> will fill an area blackish-transparent.
> 
> 2) As soon as there is at least one subpart specified that matches an
>  element, we won't draw the generic stroke/fill, but only the subpart
> ones, so this:
> 
> way [natural=water]::area { z-index: -0.1;  fill-color: #b5d6f1;
> color: #b0b0b0;} way [natural=water]::label { z-index: 5; width: 0;
> casing-width:0; text: name;} way [natural] {fill-opacity: 1.0; width:
> 1; color: black;}
> 
> will do 2 and not three strokes: the ::area and the ::label stroke.
> 
> It will use the style rules from the generic one as base, but rules 
> given for the subparts will always override the stroke style for that
>  subpart (even if the generic rule comes later in the file). That
> means the above three rules are equivalent to these 2:
> 
> /* Next rules gets fill-opacity, width, but NOT color from the
> generic as color is specified in the ::area rule */ way
> [natural=water]::area { z-index: -0.1;  fill-color: #b5d6f1; color:
> #b0b0b0; fill-opacity: 1.0; width: 1;} /* Next rules gets
> fill-opacity, color, but NOT width from the generic */ way
> [natural=water]::label { z-index: 5; width: 0; casing-width:0; text:
> name; fill-opacity: 1.0; color:black;}
> 
> 
> To sum it up, generic styles provide the base and subpart styles 
> complement and override specific styles. If there are only generic 
> styles, render that as 1 stroke, but as soon as there are subparts, 
> don't render the generic one.
> 
> 
> In my implementation: way [highway]::* is a synonym for "way
> [highway]" (the generic) which matches all subparts.
> 
> In my implementation: way [highway]:: refers to a specific subpart
> (call it __unnamed__)
> 
> Does this make sense?
> 
> Happy SOTM or where ever you are. Sebastian

Sounds good, I like the fact it is backwards compatible to style sheets
without subparts.

Question: You say that subpart styles override generic style even if it
comes later in the file. And the line

> way [highway]::*

suggests that it applies to all subparts and consequently overrides them
all if it comes later in the file. But you write it is synonym to "way
[highway]", could you clarify?

Btw., it could be useful to be able to override style for all subparts:
E.g. override the anti-aliasing for efficiency or make everything
transparent (by a certain factor (?)), ...

What is

> way [highway]::

and how is it used?


Regards, Sebastian