add a directory for plugin templates - and add a first "hello world" with basic docs"

SConstruct

@@ -326,6 +326,7 @@ opts.AddVariables(
     BoolVariable('DEMO', 'Compile demo c++ application', 'False'),
     BoolVariable('PGSQL2SQLITE', 'Compile and install a utility to convert postgres tables to sqlite', 'False'),
     BoolVariable('COLOR_PRINT', 'Print build status information in color', 'True'),
+    BoolVariable('SAMPLE_INPUT_PLUGINS', 'Compile and install sample plugins', 'False'),
     )
     
 # variables to pickle after successful configure step
@@ -1318,3 +1319,8 @@ if not HELP_REQUESTED:
 
     # write the viewer.ini file
     SConscript('demo/viewer/SConscript')
+    
+    # if requested, build the sample input plugins
+    if env['SAMPLE_INPUT_PLUGINS']:
+        SConscript('plugins/input/templates/helloworld/build.py')
+        

include/mapnik/datasource.hpp

@@ -39,6 +39,7 @@
 #include <string>
 
 namespace mapnik {
+   
 typedef MAPNIK_DECL boost::shared_ptr<Feature> feature_ptr;
     
 struct MAPNIK_DECL Featureset

plugins/input/templates/README

@@ -0,0 +1,14 @@
+template plugins
+----------------
+
+Directory to hold sample plugin templates.
+
+These are NOT intended to be used except for testing by developers.
+
+Build these plugins with:
+
+$ scons SAMPLE_INPUT_PLUGINS=True
+
+Only an ultra-simple hello world is available currently,
+but planned are example plugins templates for file-based
+and sql-based datasources.

plugins/input/templates/helloworld/README

@@ -0,0 +1,51 @@
+hello world plugin
+------------------
+
+This is a very simple sample plugin. It is designed to help developers
+see the skeletal basics needed to achieve a functional datasource plugin.
+
+Code comments attempt to highlight which code is mandatory, which is
+simply recommended, and which is purely fluff used to get the plugin to
+actually show some data.
+
+When added to a map it provides a single point geometry representing
+the center of any query. This means that it should place a point in
+the middle of any map tile and display a "hello world!" label if used like:
+
+<?xml version="1.0" encoding="utf-8"?>
+<Map srs="+init=epsg:4326" background-color="white">
+    <Style name="style">
+        <Rule>
+            <PointSymbolizer />
+            <TextSymbolizer name="[key]" face_name="DejaVu Sans Book" size="10" dx="5" dy="5"/>
+        </Rule>
+    </Style>
+    <Layer name="test" srs="+init=epsg:4326">
+        <StyleName>style</StyleName>
+        <Datasource>
+            <Parameter name="type">hello</Parameter>
+        </Datasource>
+    </Layer>
+</Map>
+
+
+Or used in python like:
+
+from mapnik2 import *
+m = Map(600,400)
+m.background = Color('white')
+s = Style()
+r = Rule()
+r.symbols.append(PointSymbolizer())
+t = TextSymbolizer(Expression("[key]"),"DejaVu Sans Book",10,Color('black'))
+t.displacement(15,15)
+r.symbols.append(t)
+s.rules.append(r)
+m.append_style('style',s)
+ds = Datasource(type="hello")
+l = Layer('test')
+l.styles.append('style')
+l.datasource = ds
+m.layers.append(l)
+m.zoom_all()
+render_to_file(m,'test.png')

plugins/input/templates/helloworld/build.py

@@ -0,0 +1,82 @@
+#!/usr/bin/env python
+
+# Mapnik uses the build tool SCons.
+
+# This python file is run to compile a plugin
+# It must be called from the main 'SConstruct' file like:
+
+# SConscript('path/to/this/file.py')
+
+# see docs at: http://www.scons.org/wiki/SConscript()
+
+import os
+
+# Give this plugin a name
+# here this happens to be the same as the directory
+PLUGIN_NAME = 'hello'
+
+# Here we pull from the SCons environment exported from the main instance
+Import ('env')
+
+# the below install details are also pulled from the
+# main SConstruct file where configuration happens
+
+# DESTDIR is default None, PREFIX is default '/usr/local/'
+install_prefix = os.path.join(env['DESTDIR'],env['PREFIX'])
+
+# LIBDIR_SCHEMA is likely either 'lib' or 'lib64', LIB_DIR_NAME is default None
+lib_name = '%s%s' % (env['LIBDIR_SCHEMA'],env['LIB_DIR_NAME'])
+
+# plugins can go anywhere, and be registered in custom locations by Mapnik
+# but the standard location is '/usr/local/lib/mapnik2/input'
+install_dest = os.path.join(install_prefix,lib_name,'input')
+
+# clone the environment here
+# so that if we modify the env it in this file
+# those changes to not pollute other builds later on...
+plugin_env = env.Clone()
+
+# Add the cpp files that need to be compiled
+plugin_sources = Split(
+	"""
+	%(PLUGIN_NAME)s_datasource.cpp
+	%(PLUGIN_NAME)s_featureset.cpp      
+	""" % locals()
+        )
+
+# Add any external libraries this plugin should
+# directly link to
+libraries = [ '' ] # eg 'libfoo'
+
+# on mac os x we need to directly link to mapnik and libicu*
+if env['PLATFORM'] == 'Darwin':
+    libraries.append('mapnik2')
+    # link libicuuc, but ICU_LIB_NAME is used custom builds of icu can
+    # have different library names like osx which offers /usr/lib/libicucore.dylib
+    libraries.append(env['ICU_LIB_NAME'])
+    
+TARGET = plugin_env.SharedLibrary(
+              # the name of the target to build, eg 'sqlite.input'
+              '../%s' % PLUGIN_NAME,
+              # prefix - normally none used
+              SHLIBPREFIX='',
+              # extension, mapnik expects '.input'
+              SHLIBSUFFIX='.input',
+              # list of source files to compile
+              source=plugin_sources,
+              # libraries to link to
+              LIBS=libraries,
+              # any custom linkflags, eg. LDFLAGS
+              # in this case CUSTOM_LDFLAGS comes
+              # from Mapnik's main SConstruct file
+              # and can be removed here if you do
+              # not need it
+              LINKFLAGS=env.get('CUSTOM_LDFLAGS')
+              )
+
+# if 'uninstall' is not passed on the command line
+# then we actually create the install targets that
+# scons will install if 'install' is passed as an arg
+if 'uninstall' not in COMMAND_LINE_TARGETS:
+    env.Install(install_dest, TARGET)
+    env.Alias('install', install_dest)

plugins/input/templates/helloworld/hello_datasource.cpp

@@ -0,0 +1,86 @@
+// file plugin
+#include "hello_datasource.hpp"
+#include "hello_featureset.hpp"
+
+using mapnik::datasource;
+using mapnik::parameters;
+
+DATASOURCE_PLUGIN(hello_datasource)
+
+hello_datasource::hello_datasource(parameters const& params, bool bind)
+   : datasource(params),
+     type_(datasource::Vector),
+     desc_(*params_.get<std::string>("type"), *params_.get<std::string>("encoding","utf-8")),
+     extent_()
+{
+    if (bind)
+    {
+        this->bind();
+    }
+}
+
+void hello_datasource::bind() const
+{
+    if (is_bound_) return;
+    
+    // every datasource must have some way of reporting its extent
+    // in this case we are not actually reading from any data so for fun
+    // let's just create a world extent in Mapnik's default srs:
+    // '+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs' (equivalent to +init=epsg:4326)
+    // see http://spatialreference.org/ref/epsg/4326/ for more details
+    extent_.init(-180,-90,180,90);
+    
+    is_bound_ = true;
+}
+
+hello_datasource::~hello_datasource() { }
+
+// This name must match the plugin filename, eg 'hello.input'
+std::string const hello_datasource::name_="hello";
+
+std::string hello_datasource::name()
+{
+    return name_;
+}
+
+int hello_datasource::type() const
+{
+    return type_;
+}
+
+mapnik::box2d<double> hello_datasource::envelope() const
+{
+    if (!is_bound_) bind();
+
+    return extent_;
+}
+
+mapnik::layer_descriptor hello_datasource::get_descriptor() const
+{
+    if (!is_bound_) bind();
+   
+    return desc_;
+}
+
+mapnik::featureset_ptr hello_datasource::features(mapnik::query const& q) const
+{
+    if (!is_bound_) bind();
+      
+    // if the query box intersects our world extent then query for features
+    if (extent_.intersects(q.get_bbox()))
+    {
+        return mapnik::featureset_ptr(new hello_featureset(q.get_bbox(),desc_.get_encoding()));
+    }
+
+    // otherwise return an empty featureset pointer
+    return mapnik::featureset_ptr();
+}
+
+mapnik::featureset_ptr hello_datasource::features_at_point(mapnik::coord2d const& pt) const
+{
+    if (!is_bound_) bind();
+
+    // features_at_point is rarely used - only by custom applications,
+    // so for this sample plugin let's do nothing...
+    return mapnik::featureset_ptr();
+}

plugins/input/templates/helloworld/hello_datasource.hpp

@@ -0,0 +1,51 @@
+#ifndef FILE_DATASOURCE_HPP
+#define FILE_DATASOURCE_HPP
+
+// mapnik
+#include <mapnik/datasource.hpp>
+
+class hello_datasource : public mapnik::datasource 
+{
+   public:
+      // constructor
+      // arguments must not change
+      hello_datasource(mapnik::parameters const& params, bool bind=true);
+      
+      // destructor
+      virtual ~hello_datasource ();
+      
+      // mandatory: type of the plugin, used to match at runtime
+      int type() const;
+
+      // mandatory: name of the plugin
+      static std::string name();
+
+      // mandatory: function to query features by box2d
+      // this is called when rendering, specifically in feature_style_processor.hpp
+      mapnik::featureset_ptr features(mapnik::query const& q) const;
+
+      // mandatory: function to query features by point (coord2d)
+      // not used by rendering, but available to calling applications
+      mapnik::featureset_ptr features_at_point(mapnik::coord2d const& pt) const;
+
+      // mandatory: return the box2d of the datasource
+      // called during rendering to determine if the layer should be processed
+      mapnik::box2d<double> envelope() const;
+      
+      // mandatory: return the layer descriptor
+      mapnik::layer_descriptor get_descriptor() const;
+      
+      // mandatory: whether to bind the datasource or delay
+      void bind() const;
+
+   private:
+      // recommended naming convention of datasource members:
+      // name_, type_, extent_, and desc_
+      static const std::string name_;
+      int type_;
+      mutable mapnik::layer_descriptor desc_;
+      mutable mapnik::box2d<double> extent_;
+};
+
+
+#endif // FILE_DATASOURCE_HPP

plugins/input/templates/helloworld/hello_featureset.cpp

@@ -0,0 +1,46 @@
+#include "hello_featureset.hpp"
+
+hello_featureset::hello_featureset(mapnik::box2d<double> const& box, std::string const& encoding)
+  : box_(box),
+    count_(0),
+    tr_(new mapnik::transcoder(encoding)) { }
+
+hello_featureset::~hello_featureset() { }
+
+mapnik::feature_ptr hello_featureset::next()
+{
+    if (!count_)
+    {
+        // create a new feature
+        mapnik::feature_ptr feature(new mapnik::Feature(count_));
+
+        // create an attribute pair of key:value
+        UnicodeString ustr = tr_->transcode("hello world!");
+        boost::put(*feature,"key",ustr);
+
+        // we need a geometry to display so just for fun here
+        // we take the center of the bbox that was used to query
+        // since we don't actually have any data to pull from...
+        mapnik::coord2d center = box_.center();
+        
+        // create a new geometry
+        mapnik::geometry2d * point = new mapnik::point_impl;
+        
+        // we use path type geometries in Mapnik to fit nicely with AGG and Cairo
+        // here we stick an x,y pair into the geometry
+        point->move_to(center.x,center.y);
+        
+        // add the geometry to the feature
+        feature->add_geometry(point);
+        
+        // increment to count so that we only return on feature
+        ++count_;
+        
+        // return the feature!
+        return feature;
+    }
+    
+    // otherwise return an empty feature_ptr
+    return mapnik::feature_ptr();
+}
+

plugins/input/templates/helloworld/hello_featureset.hpp

@@ -0,0 +1,30 @@
+#ifndef HELLO_FEATURESET_HPP
+#define HELLO_FEATURESET_HPP
+
+// mapnik
+#include <mapnik/datasource.hpp>
+
+// boost
+#include <boost/scoped_ptr.hpp> // needed for wrapping the transcoder
+
+// extend the mapnik::Featureset defined in include/mapnik/datasource.hpp
+class hello_featureset : public mapnik::Featureset
+{
+   public:
+      // this constructor can have any arguments you need
+      hello_featureset(mapnik::box2d<double> const& box, std::string const& encoding);
+      
+      // desctructor
+      virtual ~hello_featureset();
+      
+      // mandatory: you must expose a next() method, called when rendering
+      mapnik::feature_ptr next();
+   
+   private:
+      // members are up to you, but these are recommended
+      mapnik::box2d<double> const& box_;
+      mutable int count_;
+      boost::scoped_ptr<mapnik::transcoder> tr_;
+};
+
+#endif // HELLO_FEATURESET_HPP

plugins/input/templates/helloworld/test.xml

@@ -0,0 +1,19 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Map srs="+init=epsg:4326" background-color="white">
+    <Style name="style">
+        <Rule>
+            <PointSymbolizer />
+            <!-- the hello world sample hardcodes 'key' as the hypothetical field name -->
+            <TextSymbolizer name="[key]" face_name="DejaVu Sans Book" size="10" dx="5" dy="5"/>
+        </Rule>
+    </Style>
+    <!-- this example only works in EPSG:4326 -->
+    <Layer name="test" srs="+init=epsg:4326">
+        <StyleName>style</StyleName>
+        <Datasource>
+            <!-- here we create a 'hello' type datasource which simply
+            displays a point in the middle of the world's boundin box -->
+            <Parameter name="type">hello</Parameter>
+        </Datasource>
+    </Layer>
+</Map>