156a7590f4
This plugin allows you to write data sources in the Python programming language. This is useful if you want to rapidly prototype a plugin, perform some custom manipulation on data or if you want to bind mapnik to a datasource which is most conveniently accessed through Python. The plugin may be used from the existing mapnik Python bindings or it can embed the Python interpreter directly allowing it to be used from C++, XML or even JavaScript. Mapnik already has excellent Python bindings but they only directly support calling *into* mapnik *from* Python. This forces mapnik and its input plugins to be the lowest layer of the stack. The role of this plugin is to allow mapnik to call *into* Python itself. This allows mapnik to sit as rendering middleware between a custom Python frontend and a custom Python datasource. This increases the utility of mapnik as a component in a larger system. There already exists MemoryDatasource which can be used to dynamically create geometry in Python. It suffers from the problem that it does not allow generating only the geometry which is seen by a particular query. Similarly the entire geometry must exist in memory before rendering can progress. By using a custom iterator object or by using generator expressions this plugin allows geometry to be created on demand and to be destroyed after use. This can have a great impact on memory efficiency. Since geometry is generated on-demand as rendering progresses there can be arbitrarily complex 'cleverness' optimising the geometry generated for a particular query. Obvious examples of this would be generating only geometry within the query bounding box and generating geometry with an appropriate level of detail for the output resolution.
149 lines
5.8 KiB
Python
149 lines
5.8 KiB
Python
#!/usr/bin/env python
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# Mapnik uses the build tool SCons.
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# This python file is run to compile a plugin
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# It must be called from the main 'SConstruct' file like:
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# SConscript('path/to/this/file.py')
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# see docs at: http://www.scons.org/wiki/SConscript()
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import os
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# Give this plugin a name
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# here this happens to be the same as the directory
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PLUGIN_NAME = 'python'
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# Here we pull from the SCons environment exported from the main instance
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Import ('plugin_base')
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Import ('env')
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# the below install details are also pulled from the
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# main SConstruct file where configuration happens
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# plugins can go anywhere, and be registered in custom locations by Mapnik
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# but the standard location is '/usr/local/lib/mapnik/input'
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install_dest = env['MAPNIK_INPUT_PLUGINS_DEST']
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# clone the environment here
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# so that if we modify the env it in this file
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# those changes to not pollute other builds later on...
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plugin_env = plugin_base.Clone()
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# Add the cpp files that need to be compiled
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plugin_sources = Split(
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"""
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%(PLUGIN_NAME)s_datasource.cpp
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%(PLUGIN_NAME)s_featureset.cpp
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""" % locals()
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)
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# Add any external libraries this plugin should
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# directly link to
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libraries = [ '' ] # eg 'libfoo'
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libraries.append('mapnik')
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libraries.append('boost_system%s' % env['BOOST_APPEND'])
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# link libicuuc, but ICU_LIB_NAME is used custom builds of icu can
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# have different library names like osx which offers /usr/lib/libicucore.dylib
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libraries.append(env['ICU_LIB_NAME'])
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libraries.append(env['BOOST_PYTHON_LIB'])
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# TODO - do solaris/fedora need direct linking too?
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if env['PLATFORM'] == 'Darwin':
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if not env['PYTHON_DYNAMIC_LOOKUP']:
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libraries.append('png')
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if env['JPEG']:
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libraries.append('jpeg')
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libraries.append(env['ICU_LIB_NAME'])
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libraries.append('boost_regex%s' % env['BOOST_APPEND'])
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if env['THREADING'] == 'multi':
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libraries.append('boost_thread%s' % env['BOOST_APPEND'])
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##### Python linking on OS X is tricky ###
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# Confounding problems are:
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# 1) likelyhood of multiple python installs of the same major.minor version
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# because apple supplies python built-in and many users may have installed
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# further versions using macports
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# 2) boost python directly links to a python version
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# 3) the below will directly link _mapnik.so to a python version
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# 4) _mapnik.so must link to the same python lib as boost_python.dylib otherwise
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# python will Abort with a Version Mismatch error.
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# See http://trac.mapnik.org/ticket/453 for the seeds of a better approach
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# for now we offer control over method of direct linking...
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# The default below is to link against the python dylib in the form of
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#/path/to/Python.framework/Python instead of -lpython
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# http://developer.apple.com/mac/library/DOCUMENTATION/Darwin/Reference/ManPages/man1/ld.1.html
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if env['PYTHON_DYNAMIC_LOOKUP']:
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python_link_flag = '-undefined dynamic_lookup'
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elif env['FRAMEWORK_PYTHON']:
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if env['FRAMEWORK_SEARCH_PATH']:
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# if the user has supplied a custom root path to search for
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# a given Python framework, then use that to direct the linker
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python_link_flag = '-F%s -framework Python -Z' % env['FRAMEWORK_SEARCH_PATH']
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else:
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# otherwise be as explicit as possible for linking to the same Framework
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# as the executable we are building with (or is pointed to by the PYTHON variable)
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# otherwise we may accidentally link against either:
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# /System/Library/Frameworks/Python.framework/Python/Versions/
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# or
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# /Library/Frameworks/Python.framework/Python/Versions/
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# See: http://trac.mapnik.org/ticket/380
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link_prefix = env['PYTHON_SYS_PREFIX']
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if '.framework' in link_prefix:
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python_link_flag = '-F%s -framework Python -Z' % os.path.dirname(link_prefix.split('.')[0])
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elif '/System' in link_prefix:
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python_link_flag = '-F/System/Library/Frameworks/ -framework Python -Z'
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else:
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# should we fall back to -lpython here?
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python_link_flag = '-F/ -framework Python'
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# if we are not linking to a framework then use the *nix standard approach
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else:
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# TODO - do we need to pass -L/?
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python_link_flag = '-lpython%s' % env['PYTHON_VERSION']
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elif env['PLATFORM'] == 'SunOS':
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# make sure to explicitly link mapnik.so against
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# libmapnik in its installed location
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python_link_flag = '-R%s' % env['MAPNIK_LIB_BASE']
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else:
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# all other platforms we don't directly link python
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python_link_flag = ''
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if env['CUSTOM_LDFLAGS']:
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linkflags = '%s %s' % (env['CUSTOM_LDFLAGS'], python_link_flag)
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else:
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linkflags = python_link_flag
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plugin_env.Append(CPPPATH = env['PYTHON_INCLUDES'])
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TARGET = plugin_env.SharedLibrary(
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# the name of the target to build, eg 'sqlite.input'
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'../%s' % PLUGIN_NAME,
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# prefix - normally none used
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SHLIBPREFIX='',
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# extension, mapnik expects '.input'
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SHLIBSUFFIX='.input',
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# list of source files to compile
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source=plugin_sources,
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# libraries to link to
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LIBS=libraries,
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# any custom linkflags, eg. LDFLAGS
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# in this case CUSTOM_LDFLAGS comes
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# from Mapnik's main SConstruct file
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# and can be removed here if you do
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# not need it
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LINKFLAGS=env.get('CUSTOM_LDFLAGS')
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)
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# if 'uninstall' is not passed on the command line
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# then we actually create the install targets that
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# scons will install if 'install' is passed as an arg
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if 'uninstall' not in COMMAND_LINE_TARGETS:
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env.Install(install_dest, TARGET)
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env.Alias('install', install_dest)
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