Tough problem, providing an alternate solution for discussion only (not
criticism of your two ideas).
> However that has some limitations, in that we could support only
> one image filter per feature type style, whilst Mapnik supports
> a chain of them.
> They actually do that in a single attribute, sticking filter params in
> it too:
>
> image-filter="grey|blur:rx=4,ry=4|emboss|..."/
> Hum... that seems a bit extreme, on the other side if we are going
> to support many of them in a single vendor option, I don't see
> a way out.
>
>
>
Let me try another one …
1) Each FeatureTypeStyle has a list of Rules
2) One of the Rules can be marked as "other" (that is provides a isElseFilter
() True rather rather than a Filter), this acts as a "catch all" for any
features that were not other wise rendered .. in a sense this Rule is acting on
the entire FeatureType Style
3) So here is the counter proposal
- Make a Rule.isComposition() that acts on the entire FeatureTypeStyle (after
the other rules have had a go at it)
- Allow it to provide a list of symbolisers
- The RasterSymbolizer controlling bands and so forth can be used almost as is
(in order to represent the simple alpha or colour manipulations)
- RasterSymbolizers with r=1.0,g=1.0,b=1.0 can be combined with vendor
parameters for the other senarios you describe below
<Rule>
<Composition/>
<RasterSymbolizer>
<Opacity>1.0</Opacity>
…
<ContrastEnhancement>
<GammaValue>1.0</GammaValue>
</ContrastEnhancement>
</RasterSymbolizer>
</Rule>
And the list of RasterSymbolizers can form your "chain".
This has the advantage of keep vendor options in the same spot, to other
systems the
Rules will not appear to have any content to work etc…
So smaller API change, does it make sense?
Jody------------------------------------------------------------------------------
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