SCons 3.0.1: Agg库与Mapnik Python绑定教程

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SCons 3.0.1 是一个强大的构建工具，主要用于软件开发过程中自动化构建过程。"scons-man"文档提供了关于SCons的详细命令行帮助和参考手册，涵盖了其核心功能、配置选项以及与Mapnik（一个流行的地图渲染引擎）相关的集成。在SCons 3.0.1中，目录结构包含了多个关键组件和模块： 1. src/agg: 这个目录包含Agg图形库的源代码，它是Mapnik的重要组成部分，负责2D矢量图形的渲染。包括agg_renderer.os、agg_vcgen_markers_term.o、agg_line_aa_basics.o等，这些都是图形处理的核心文件，涉及路径绘制、抗锯齿等技术。 2. bindings/python: 这个部分是Python绑定，提供了与Mapnik交互的接口。有mapnik_symbolizer.os、mapnik_font_engine.os、mapnik_view_transform.os、mapnik_image.os等，用于处理地图符号化、字体渲染、视图变换和图像操作。 3. plugins: 插件目录，包括输入（shapefile.os、dbffile.os、rasterinput.os）、输出（如保存地图的save_map.os）和与OGC（开放地理编码）服务器相关的模块（ogcserver）。 4. font_engine_freetype: 提供FreeType字体引擎支持，对于处理各种字体至关重要。 5. color 和 stroke: 分别与颜色处理和描边效果相关。 6. image_util: 图像处理实用工具，可能用于图像预处理或格式转换。 7. mapnik_datasource_cache: 数据源缓存管理，提高数据访问效率。 8. include: 包含头文件，定义了SCons与Mapnik交互所需的API。 9. mapnik_rule.os: 规则处理模块，用于定义地图渲染规则。 10. agg_bezier_arc.o 和 agg_arc.o: 处理贝塞尔曲线和圆弧的函数。 11. raster: 包括输入和输出的栅格数据处理，如raster_datasource.os和raster_featureset.os。 12. unicode: 处理Unicode字符集，确保地图上的文本显示正确。 13. mapnik_map.os: 最终生成地图对象的模块。 14. arrow: 可能与箭头符号相关的处理。通过这些文件和目录，SCons 3.0.1能够有效地组织和构建Mapnik项目，自动化编译过程，确保不同模块之间的协调工作，并提供Python脚本的接口，使得用户能够方便地定制地图渲染逻辑和数据处理。使用这个版本的SCons，开发者可以更快地迭代和优化地图应用，提高开发效率。

CONFIGURATION FILE REFERENCE

Construction Environments

A construction environment is the basic means by which the SConscript files communicate build information to scons.

A new construction environment is created using the Environment function:

env = Environment()

Variables, called construction variables, may be set in a construction environment either by specifying them as key-

words when the object is created or by assigning them a value after the object is created:

env = Environment(FOO = 'foo')

env['BAR'] = 'bar'

As a convenience, construction variables may also be set or modified by the parse_flags keyword argument, which

applies the ParseFlags method (described below) to the argument value after all other processing is completed. This

is useful either if the exact content of the flags is unknown (for example, read from a control file) or if the flags are

distributed to a number of construction variables.

env = Environment(parse_flags = '-Iinclude -DEBUG -lm')

This example adds 'include' to CPPPATH, 'EBUG' to CPPDEFINES, and 'm' to LIBS.

By default, a new construction environment is initialized with a set of builder methods and construction variables

that are appropriate for the current platform. An optional platform keyword argument may be used to specify that an

environment should be initialized for a different platform:

env = Environment(platform = 'cygwin')

env = Environment(platform = 'os2')

env = Environment(platform = 'posix')

env = Environment(platform = 'win32')

Specifying a platform initializes the appropriate construction variables in the environment to use and generate file

names with prefixes and suffixes appropriate for the platform.

Note that the win32 platform adds the SystemDrive and SystemRoot variables from the user's external environ-

ment to the construction environment's ENV dictionary. This is so that any executed commands that use sock-

ets to connect with other systems (such as fetching source files from external CVS repository specifications like

:pserver:anonymous@cvs.sourceforge.net:/cvsroot/scons) will work on Windows systems.

The platform argument may be function or callable object, in which case the Environment() method will call the

specified argument to update the new construction environment:

def my_platform(env):

env['VAR'] = 'xyzzy'

env = Environment(platform = my_platform)

Additionally, a specific set of tools with which to initialize the environment may be specified as an optional keyword

argument:

env = Environment(tools = ['msvc', 'lex'])

Non-built-in tools may be specified using the toolpath argument:

env = Environment(tools = ['default', 'foo'], toolpath = ['tools'])

This looks for a tool specification in tools/foo.py (as well as using the ordinary default tools for the platform). foo.py

should have two functions: generate(env, **kw) and exists(env). The generate() function modifies the passed-

in environment to set up variables so that the tool can be executed; it may use any keyword arguments that the user

supplies (see below) to vary its initialization. The exists() function should return a true value if the tool is available.

Tools in the toolpath are used before any of the built-in ones. For example, adding gcc.py to the toolpath would override

the built-in gcc tool. Also note that the toolpath is stored in the environment for use by later calls to Clone() and

Tool() methods:

base = Environment(toolpath=['custom_path'])

derived = base.Clone(tools=['custom_tool'])

derived.CustomBuilder()

The elements of the tools list may also be functions or callable objects, in which case the Environment() method will

call the specified elements to update the new construction environment:

def my_tool(env):

env['XYZZY'] = 'xyzzy'

env = Environment(tools = [my_tool])

The individual elements of the tools list may also themselves be two-element lists of the form (toolname, kw_dict).

SCons searches for the toolname specification file as described above, and passes kw_dict, which must be a dictionary,

as keyword arguments to the tool's generate function. The generate function can use the arguments to modify the

tool's behavior by setting up the environment in different ways or otherwise changing its initialization.

# in tools/my_tool.py:

def generate(env, **kw):

# Sets MY_TOOL to the value of keyword argument 'arg1' or 1.

env['MY_TOOL'] = kw.get('arg1', '1')

def exists(env):

return 1

# in SConstruct:

env = Environment(tools = ['default', ('my_tool', {'arg1': 'abc'})],

toolpath=['tools'])

The tool definition (i.e. my_tool()) can use the PLATFORM variable from the environment it receives to customize

the tool for different platforms.

If no tool list is specified, then SCons will auto-detect the installed tools using the PATH variable in the ENV con-

struction variable and the platform name when the Environment is constructed. Changing the PATH variable after the

Environment is constructed will not cause the tools to be redetected.

One feature now present within Scons is the ability to have nested tools. Tools which can be located within a subdi-

rectory in the toolpath. With a nested tool name the dot represents a directory seperator

Sets: $DC, $DCOM, $DDEBUG, $DDEBUGPREFIX, $DDEBUGSUFFIX, $DFILESUFFIX, $DFLAGPRE-

FIX, $DFLAGS, $DFLAGSUFFIX, $DINCPREFIX, $DINCSUFFIX, $DLIB, $DLIBCOM, $DLIB-

DIRPREFIX, $DLIBDIRSUFFIX, $DLIBFLAGPREFIX, $DLIBFLAGSUFFIX, $DLIBLINKPREFIX,

$DLIBLINKSUFFIX, $DLINK, $DLINKCOM, $DLINKFLAGPREFIX, $DLINKFLAGS, $DLINKFLAGSUF-

FIX, $DPATH, $DRPATHPREFIX, $DRPATHSUFFIX, $DShLibSonameGenerator, $DVERPREFIX,

$DVERSIONS, $DVERSUFFIX, $SHDC, $SHDCOM, $SHDLIBVERSION, $SHDLIBVERSIONFLAGS,

$SHDLINK, $SHDLINKCOM, $SHDLINKFLAGS.

docbook

This tool tries to make working with Docbook in SCons a little easier. It provides several toolchains for creating

different output formats, like HTML or PDF. Contained in the package is a distribution of the Docbook XSL

stylesheets as of version 1.76.1. As long as you don't specify your own stylesheets for customization, these official

versions are picked as default...which should reduce the inevitable setup hassles for you.

Implicit dependencies to images and XIncludes are detected automatically if you meet the HTML requirements.

The additional stylesheet utils/xmldepend.xsl by Paul DuBois is used for this purpose.

Note, that there is no support for XML catalog resolving offered! This tool calls the XSLT processors and PDF

renderers with the stylesheets you specified, that's it. The rest lies in your hands and you still have to know what

you're doing when resolving names via a catalog.

For activating the tool "docbook", you have to add its name to the Environment constructor, like this

env = Environment(tools=['docbook'])

On its startup, the Docbook tool tries to find a required xsltproc processor, and a PDF renderer, e.g. fop. So

make sure that these are added to your system's environment PATH and can be called directly, without specifying

their full path.

For the most basic processing of Docbook to HTML, you need to have installed

• the Python lxml binding to libxml2, or

• the direct Python bindings for libxml2/libxslt, or

• a standalone XSLT processor, currently detected are xsltproc, saxon, saxon-xslt and xalan.

Rendering to PDF requires you to have one of the applications fop or xep installed.

Creating a HTML or PDF document is very simple and straightforward. Say

env = Environment(tools=['docbook'])

env.DocbookHtml('manual.html', 'manual.xml')

env.DocbookPdf('manual.pdf', 'manual.xml')

to get both outputs from your XML source manual.xml. As a shortcut, you can give the stem of the filenames

alone, like this:

env = Environment(tools=['docbook'])

env.DocbookHtml('manual')

env.DocbookPdf('manual')

and get the same result. Target and source lists are also supported:

env = Environment(tools=['docbook'])

env.DocbookHtml(['manual.html','reference.html'], ['manual.xml','reference.xml'])

or even

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