add support for halo-rasterizer for shields - closes #2226

src/load_map.cpp

@@ -1309,6 +1309,8 @@ void map_parser::parse_shield_symbolizer(rule & rule, xml_node const& sym)
         ensure_exists(file);
         shield_symbol.set_filename( parse_path(file, sym.get_tree().path_expr_grammar) );
         parse_symbolizer_base(shield_symbol, sym);
+        optional<halo_rasterizer_e> halo_rasterizer = sym.get_opt_attr<halo_rasterizer_e>("halo-rasterizer");
+        if (halo_rasterizer) shield_symbol.set_halo_rasterizer(*halo_rasterizer);
         rule.append(shield_symbol);
     }
     catch (config_error const& ex)

tests/visual_tests/styles/shield-on-line-spacing-eq-width.xml

@@ -69,6 +69,7 @@
               face-name="DejaVu Sans Book"
               halo-fill="white"
               halo-radius="2"
+              halo-rasterizer="fast"
               spacing="15">
             'hi'
             </ShieldSymbolizer>