add 'gamma' attribute to PolygonSymbolizer, along with tests against simplified world borders shapefile - setting gamma to .5-.7 can remove gaps in processed_p.shp depending on background color - closes #428

CHANGELOG

@@ -81,6 +81,10 @@ Mapnik 0.7.0 Release
 
 - PNG: Added support for semitransparency in png256 outpuy (#477,#202)
 
+- PolygonSymbolizer: Added 'gamma' attribute to allow for dilation of polygon edges - a solution
+  to gap artifacts or "ghost lines" between adjacent polygons and allows for slight sharpening of
+  the edges of non overlapping polygons. Accepts any values but 0-1 is the recommended range.
+   
 - TextSymbolizer: Large set of new attributes: 'text_convert', 'line_spacing', 'character_spacing', 
   'wrap_character', 'wrap_before', 'horizontal_alignment', 'justify_alignment', and 'opacity'.
 

bindings/python/mapnik_polygon_symbolizer.cpp

@@ -38,23 +38,24 @@ struct polygon_symbolizer_pickle_suite : boost::python::pickle_suite
    static  boost::python::tuple
    getstate(const polygon_symbolizer& p)
    {
-        return boost::python::make_tuple(p.get_opacity());
+        return boost::python::make_tuple(p.get_opacity(),p.get_gamma());
    }
 
    static void
    setstate (polygon_symbolizer& p, boost::python::tuple state)
    {
         using namespace boost::python;
-        if (len(state) != 1)
+        if (len(state) != 2)
         {
             PyErr_SetObject(PyExc_ValueError,
-                         ("expected 1-item tuple in call to __setstate__; got %s"
+                         ("expected 2-item tuple in call to __setstate__; got %s"
                           % state).ptr()
             );
             throw_error_already_set();
         }
                 
         p.set_opacity(extract<float>(state[0]));
+        p.set_gamma(extract<float>(state[1]));
    }
 
 };
@@ -74,6 +75,9 @@ void export_polygon_symbolizer()
         .add_property("fill_opacity",
                       &polygon_symbolizer::get_opacity,
                       &polygon_symbolizer::set_opacity)
+        .add_property("gamma",
+                      &polygon_symbolizer::get_gamma,
+                      &polygon_symbolizer::set_gamma)
         ;    
 
 }

include/mapnik/polygon_symbolizer.hpp

@@ -33,11 +33,13 @@ namespace mapnik
     {
         explicit polygon_symbolizer() 
             : fill_(color(128,128,128)),
-              opacity_(1.0) {}
+              opacity_(1.0),
+              gamma_(1.0) {}
 
         polygon_symbolizer(color const& fill)
             : fill_(fill),
-              opacity_(1.0) {}
+              opacity_(1.0),
+              gamma_(1.0) {}
         
         color const& get_fill() const
         {
@@ -55,9 +57,19 @@ namespace mapnik
         {
             return opacity_;
         }
+        void set_gamma(float gamma)
+        {
+            gamma_ = gamma;
+        }
+        float get_gamma() const
+        {
+            return gamma_;
+        }
+
     private:
         color fill_;
         float opacity_;
+        float gamma_;
     }; 
    
    struct MAPNIK_DECL building_symbolizer

src/agg_renderer.cpp

@@ -188,6 +188,8 @@ namespace mapnik
       renderer ren(renb);
 
       ras_ptr->reset();
+            
+      ras_ptr->gamma(agg::gamma_linear(0.0, sym.get_gamma()));
 
       for (unsigned i=0;i<feature.num_geometries();++i)
       {

src/load_map.cpp

@@ -1487,6 +1487,11 @@ namespace mapnik
                   float opacity = get_css<float>(css, css_name);
                   poly_sym.set_opacity(opacity);
                }
+               else if (css_name == "gamma")
+               {
+                   float gamma = get_css<float>(css, css_name);
+                   poly_sym.set_gamma(gamma);
+               }
                else
                {
                   throw config_error(std::string("Failed to parse unknown CSS ") +

src/save_map.cpp

@@ -128,6 +128,10 @@ namespace mapnik
                 {
                     set_css( sym_node, "fill-opacity", sym.get_opacity() );
                 }
+                if ( sym.get_gamma() != dfl.get_gamma() || explicit_defaults_ )
+                {
+                    set_css( sym_node, "gamma", sym.get_gamma() );
+                }
             }
 
             void operator () ( const polygon_pattern_symbolizer & sym )

tests/data/good_maps/agg_poly_gamma_map.xml

@@ -0,0 +1,61 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Map srs="+proj=merc +lon_0=0 +lat_ts=0 +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs" bgcolor="steelblue">
+    <Style name="world_merc20090930161252883_style">
+        
+        <!-- Asia - default dark color behind light polygon 
+        leads to "ghost lines" show-through
+        -->
+        
+        <Rule>
+            <Filter>([REGION]=142)</Filter>
+            <PolygonSymbolizer>
+                <CssParameter name="fill">yellow</CssParameter>
+            </PolygonSymbolizer>
+        </Rule>
+
+        <!-- Europe, using Opacity avoids "ghost lines" 
+        -->
+        <Rule>
+            <Filter>([REGION]=150)</Filter>
+            <PolygonSymbolizer>
+                <CssParameter name="fill">rgb(176,151,238)</CssParameter>
+                <CssParameter name="fill-opacity">.3</CssParameter>
+            </PolygonSymbolizer>
+        </Rule>
+        
+        <!-- Americas, using gamma of .65 to remove blue lines works as well..
+        -->
+        <Rule>
+            <Filter>([REGION]=19)</Filter>
+            <PolygonSymbolizer>
+                <CssParameter name="fill">rgb(136,172,2)</CssParameter>
+                <CssParameter name="gamma">.6</CssParameter>
+            </PolygonSymbolizer>
+        </Rule>
+
+        <!-- Africa, using gamma of .65 to remove blue lines works as well..
+        -->
+        <Rule>
+            <Filter>([REGION]=2)</Filter>
+            <PolygonSymbolizer>
+                <CssParameter name="fill">rgb(239,98,133)</CssParameter>
+                <CssParameter name="gamma">.65</CssParameter>
+            </PolygonSymbolizer>
+        </Rule>
+
+        <!-- Oceana, all disjunct polygons so it does not matter -->
+        <Rule>
+            <Filter>([REGION]=9)</Filter>
+            <PolygonSymbolizer>
+                <CssParameter name="fill">rgb(212,9,14)</CssParameter>
+            </PolygonSymbolizer>
+        </Rule>
+    </Style>
+    <Layer name="world_merc20090930161252883" srs="+proj=merc +lon_0=0 +lat_ts=0 +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs" status="1" clear_label_cache="0" queryable="1">
+        <StyleName>world_merc20090930161252883_style</StyleName>
+        <Datasource>
+            <Parameter name="file">../../data/shp/world_merc</Parameter>
+            <Parameter name="type">shape</Parameter>
+        </Datasource>
+    </Layer>
+</Map>

tests/data/shp/world_merc.prj

@@ -0,0 +1 @@
+PROJCS["Google Maps Global Mercator",GEOGCS["GCS_WGS_1984",DATUM["D_WGS_1984",SPHEROID["WGS_1984",6378137,298.257223563]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Mercator_2SP"],PARAMETER["standard_parallel_1",0],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian",0],PARAMETER["false_easting",0],PARAMETER["false_northing",0],UNIT["Meter",1]]

tests/data/shp/world_merc_license.txt

@@ -0,0 +1,85 @@
+world_merc
+==========
+
+'world_merc.shp' is a version of TM_WORLD_BORDERS_SIMPL-0.3.shp
+downloaded from http://thematicmapping.org/downloads/world_borders.php.
+
+Coodinates near 180 degress longitude were clipped to faciliate reprojection
+to Google mercator (EPSG:900913).
+
+Details from original readme are below:
+
+-------------
+
+TM_WORLD_BORDERS-0.1.ZIP 
+
+Provided by Bjorn Sandvik, thematicmapping.org
+
+Use this dataset with care, as several of the borders are disputed.
+
+The original shapefile (world_borders.zip, 3.2 MB) was downloaded from the Mapping Hacks website:
+http://www.mappinghacks.com/data/
+
+The dataset was derived by Schuyler Erle from public domain sources.
+Sean Gilles did some clean up and made some enhancements.
+
+
+COLUMN		TYPE			DESCRIPTION
+
+Shape		Polygon			Country/area border as polygon(s)
+FIPS		String(2)		FIPS 10-4 Country Code
+ISO2		String(2)		ISO 3166-1 Alpha-2 Country Code
+ISO3		String(3)		ISO 3166-1 Alpha-3 Country Code
+UN		Short Integer(3)	ISO 3166-1 Numeric-3 Country Code 
+NAME		String(50)		Name of country/area
+AREA		Long Integer(7)		Land area, FAO Statistics (2002) 
+POP2005		Double(10,0)	 	Population, World Polulation Prospects (2005)
+REGION		Short Integer(3) 	Macro geographical (continental region), UN Statistics
+SUBREGION	Short Integer(3)	Geogrpahical sub-region, UN Statistics
+LON		FLOAT (7,3)		Longitude
+LAT		FLOAT (6,3)		Latitude
+
+
+CHANGELOG VERSION 0.3 - 30 July 2008
+
+- Corrected spelling mistake (United Arab Emirates)
+- Corrected population number for Japan
+- Adjusted long/lat values for India, Italy and United Kingdom
+
+
+CHANGELOG VERSION 0.2 - 1 April 2008
+
+- Made new ZIP archieves. No change in dataset.
+
+
+CHANGELOG VERSION 0.1 - 13 March 2008
+
+- Polygons representing each country were merged into one feature
+- ≈land Islands was extracted from Finland
+- Hong Kong was extracted from China
+- Holy See (Vatican City) was added
+- Gaza Strip and West Bank was merged into "Occupied Palestinean Territory"
+- Saint-Barthelemy was extracted from Netherlands Antilles
+- Saint-Martin (Frensh part) was extracted from Guadeloupe
+- Svalbard and Jan Mayen was merged into "Svalbard and Jan Mayen Islands"
+- Timor-Leste was extracted from Indonesia
+- Juan De Nova Island was merged with "French Southern & Antarctic Land"
+- Baker Island, Howland Island, Jarvis Island, Johnston Atoll, Midway Islands
+  and Wake Island was merged into "United States Minor Outlying Islands"
+- Glorioso Islands, Parcel Islands, Spartly Islands was removed 
+  (almost uninhabited and missing ISO-3611-1 code)
+
+- Added ISO-3166-1 codes (alpha-2, alpha-3, numeric-3). Source:
+  https://www.cia.gov/library/publications/the-world-factbook/appendix/appendix-d.html
+  http://unstats.un.org/unsd/methods/m49/m49alpha.htm
+  http://www.fysh.org/~katie/development/geography.txt
+- AREA column has been replaced with data from UNdata:
+  Land area, 1000 hectares, 2002, FAO Statistics
+- POPULATION column (POP2005) has been replaced with data from UNdata:
+  Population, 2005, Medium variant, World Population Prospects: The 2006 Revision
+- Added region and sub-region codes from UN Statistics Division. Source:
+  http://unstats.un.org/unsd/methods/m49/m49regin.htm
+- Added LAT, LONG values for each country
+
+
+