A proposal to implement named styles and labels in MapServer

Proposed Map File Syntax Example

MAP
  STYLE
    # define a named style with global visibility
    NAME "some_style"
    ...
  END
  ...
  LAYER
    NAME "uses_a_style"
    CLASS
       # a name instead of a block means 'use the named style directly'
       STYLE "some_style"
       ...
    END
  END
  LAYER 
    NAME "extends_a_style"
    CLASS
      STYLE
        # inside a style block, pull in properties from another style
        # then make custom changes for this LAYER/CLASS
        EXTENDS "some_style"
        ...
      END
    END
  END
END

Mapfile Extensions

• Enable STYLE blocks at the top MAP level
  • Add a NAME directive to the STYLE block
  • Top-level STYLE blocks must be named

• Provide a "named style" declaration in the LAYER block in the form of LAYER "name" (in addition to the existing LAYER ... END syntax)
  • The LAYER object gets instantiated with a copy of the named style from the top level
  • Referencing a non-existent STYLE by name throws an exception

• Add an EXTENDS "style" directive to the STYLE block
  • Block styles that inherit from a named style are instantied as a copy of the named style before other declarations in the STYLE block are applied

MapServer StyleObj Extensions

• Add a "name" property to styleObj
• Add a "shared" property to styleObj
  • Exporting a map file would emit all styleObjs with style.shared set to true at the top level
  • Programmatic changes to shared styles *would* affect all classes using that style
  • If you don't want that behavior, use cloneStyle/EXTENDS
• Add a "cloneStyle" function to mapfile.c
  • This would be the programmatic interface for EXTENDS
  • cloneStyle would presumably copy a top-level style and set the new object's shared property to false
• Look at INLINESYMBOLS(?) for exporting styles
• Possibly have the styles cacaded at render time rather than at mapfile parse time and work around the default issues

MapScript? Extensions

• ...?