====== A guide to filters in atFilterAM ======


===== Filters =====

A //filter// is a set of rules (or //layers//) that are used to convert an attributes map into a set of alpha maps (e.g. [[plugins:calc:atFilterAM:alphaexpress|Alpha express]]), or to combine land types in an attributes map (e.g. [[plugins:calc:atFilterAM:filterAM|Filtering the attributes map]]).

Each filter consists of a number of layers. You can see and edit the layers in a filter using the [[plugins:calc:atfilteram:filtereditor|filter editor]]:

{{ :plugins:calc:atfilteram:filteredit.png |:plugins:calc:atfilteram:filteredit.png}}


===== Layers =====

When a filter is applied to the attributes map, each //layer// in the filter will convert one or more land type(s) in the attributes map into one output alpha layer. For example, a "rock" filter may combine the "cliffs" and "pebbles" land types to produce a merged alpha layer for the two. 

Each layer consists of one or more //string(s)//. These strings determine which land types will contribute to the output alpha layer produced by a filter layer. You can see and edit the strings in a filter using the [[plugins:calc:atfilteram:filterlayereditor|filter layer editor]]:

{{ :plugins:calc:atfilteram:layeredit.png |:plugins:calc:atfilteram:layeredit.png}}

===== Strings =====

The strings in a filter layer are used to match the land types in the attributes map with the filter layer. For example, a string such as "grass" will match-up with any land type that has "grass" anywhere in its name. 

A land type with the wildcard "*" will match against every land type. This is typically used for the 'default' filter layer. A wildcard land type should be placed //last// in the layer list (see [[plugins:calc:atFilterAM:filtereditor|filter editor]]).