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author | Norbert Preining <norbert@preining.info> | 2019-09-02 13:46:59 +0900 |
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committer | Norbert Preining <norbert@preining.info> | 2019-09-02 13:46:59 +0900 |
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tree | 60335e10d2f4354b0674ec22d7b53f0f8abee672 /graphics/pgf/base/doc/text-en/pgfmanual-en-dv-main.tex |
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diff --git a/graphics/pgf/base/doc/text-en/pgfmanual-en-dv-main.tex b/graphics/pgf/base/doc/text-en/pgfmanual-en-dv-main.tex new file mode 100644 index 0000000000..26a97fa4e7 --- /dev/null +++ b/graphics/pgf/base/doc/text-en/pgfmanual-en-dv-main.tex @@ -0,0 +1,828 @@ +% Copyright 2008 by Till Tantau +% +% This file may be distributed and/or modified +% +% 1. under the LaTeX Project Public License and/or +% 2. under the GNU Free Documentation License. +% +% See the file doc/generic/pgf/licenses/LICENSE for more details. + + +\section{Creating Data Visualizations} +\label{section-dv-main} +\label{section-dv-main-setup} + +\subsection{Overview} + +The \todosp{why two labels? The first doesn't seem to be used.} present section +explains how a data visualization is created in \tikzname. For this, you need +to include the |datavisualization| library and then use the command +|\datavisualization| whose syntax is explained in the rest of the present +section. This command is part of the following library: + +\begin{tikzlibrary}{datavisualization} + This library must be loaded if you wish to use the |\datavisualization| + command. It defines all styles needed to create basic data visualizations; + additional, more specialized libraries need to be loaded for more advanced + features. +\end{tikzlibrary} + +In order to visualize, you basically need to do three things: +% +\begin{enumerate} + \item You need to select what kind of plot you would like to have (a + ``school book plot'' or a ``scientific 2d plot'' or a ``scientific + spherical plot'' etc.). This is done by passing an option to the + |\datavisualization| command that selects this kind of plot. + \item You need to provide data points, which is done using the |data| + command. + \item Additionally, you can add options that give you more fine-grained + control over the way the visualization will look. You can configure the + number of ticks and grid lines, where the labels are placed, the + colors, or the fonts. Indeed, since the data visualization engine + internally uses \tikzname-styles, you can have extremely fine-grained + control over how a plot will look like. +\end{enumerate} + +The syntax of the |\datavisualization| command is designed in such a way that +if you only need to provide very few options to create plots that ``look good +by default''. + +This section is structured as follows: First, the philosophy behind concepts +like ``data points'', ``axes'', or ``visualizers'' is explained. Each of these +concepts is further detailed in later section. Then, the syntax of the +|\datavisualization| command is covered. The reference sections explain which +predefined plot kinds are available. + + +\subsection{Concept: Data Points and Data Formats} + +As explained in Section~\ref{section-dv-intro-data-points}, data points are the +basic entities that are processed by the data visualization engine. In order to +specify data points, you use the |data| command, whose syntax is explained in +more detail in Section~\ref{section-dv-data-syntax}. The |data| command allows +you to either specify points ``inline'', directly inside your \TeX-file; or you +can specify the name of file that contains the data points. + +\medskip +\textbf{Specifying data points.} +Data points can be formatted in different ways. For instance, in the so called +\emph{comma separated values} format, there is one line for each data point and +the different attributes of a data point are separated by commas. Another +common format is to specify data points using the so called \emph{key--value} +format, where on each line the different attributes of a data point are set +using a comma-separated list of strings of the form |attribute=value|. + +Here are two examples, where similar data is given in different formats: +% +\begin{codeexample}[] +\begin{tikzpicture} + \datavisualization [school book axes, visualize as smooth line] + data { + x, y + -1.5, 2.25 + -1, 1 + -.5, .25 + 0, 0 + .5, .25 + 1, 1 + 1.5, 2.25 + }; +\end{tikzpicture} +\end{codeexample} + +\begin{codeexample}[] +\begin{tikzpicture} + \datavisualization [school book axes, visualize as smooth line] + data [format=function] { + var x : interval [-1.5:1.5] samples 7; + func y = \value x*\value x; + }; +\end{tikzpicture} +\end{codeexample} + +In the first example, no format needed to be specified explicitly since the +default format is the one used for the data following the |data| keyword: A +list of comma-separated values, where each line represents a data point. + +\medskip +\textbf{Number accuracy.}\label{section-dv-expressions} +Data visualizations typically demand a much higher accuracy and range of values +than \TeX\ provides: \TeX\ numbers are limited to 13 bits for the integer part +and 16 bits for the fractional part. Because of this, the data visualization +engine does not use \pgfname's standard representation of numbers and \TeX\ +dimensions and is does not use the standard parser when reading numbers in a +data point. Instead, the |fpu| library, described in +Section~\ref{section-library-fpu}, is used to handle numbers. + +This use of the |fpu| library has several effects that users of the data +visualization system should be aware of: +% +\begin{enumerate} + \item You can use numbers like |100000000000000| or |0.00000000001| in a + data points. + \item Since the |fpu| library does not support advanced parsing, you + currently \emph{cannot} write things like |3+2| in a data point number. + This will result in an error. + \item However, there is a loop-hole: If a ``number'' in a data point starts + with a parenthesis, the value between the parentheses \emph{is} parsed + using the normal parser: + % + \begin{itemize} + \item |100000| is allowed. + \item |2+3| yields an error. + \item |(2+3)| is allowed and evaluates to |5|. + \item |(100000)| yields an error since $100\,000$ is beyond the + normal parser's precision. + \end{itemize} + % + The bottom line is that any normal calculations should be set inside + round parentheses, while large numbers should not be surrounded by + parentheses. Hopefully, in the future, these restrictions will be + lifted. +\end{enumerate} + +Section~\ref{section-dv-formats} gives an in-depth coverage of the available +data formats and explains how new data formats can be defined. + + +\subsection{Concept: Axes, Ticks, and Grids} + +Most plots have two or three axes: A horizontal axis usually called the +$x$-axis, a vertical axis called the $y$-axis, and possibly some axis pointing +in a sloped direction called the $z$-axis. Axes are usually drawn as lines with +\emph{ticks} indicating interesting positions on the axes. The data +visualization engine gives you detailed control over where these ticks are +rendered and how many of them are used. Great care is taken to ensure that the +position of ticks are chosen well by default. + +From the point of view of the data visualization engine, axes are a somewhat +more general concept than ``just'' lines that point ``along'' some dimension: +The data visualization engine uses axes to visualize any change of an attribute +by varying the position of data points in the plane. For instance, in a polar +plot, there is an ``axis'' for the angle and another ``axis'' for the distance +if the point from the center. Clearly these axes vary the position of data +points in the plane according to some attribute of the data points; but just as +clearly they do not point in any ``direction''. + +A great benefit of this approach is that the powerful methods for specifying +and automatic inference of ``good'' positions for ticks or grid lines apply to +all sorts of situations. For instance, you can use it to automatically put +ticks and grid lines at well-chosen angles of a polar plot. + +Typically, you will not need to specify axes explicitly. Rather, predefined +styles take care of this for you: +% +\begin{codeexample}[] +\begin{tikzpicture} + \datavisualization [ + scientific axes, + x axis={length=3cm, ticks=few}, + visualize as smooth line + ] + data [format=function] { + var x : interval [-1.5:1.5] samples 7; + func y = \value x*\value x; + }; +\end{tikzpicture} +\end{codeexample} + +\begin{codeexample}[] +\begin{tikzpicture} + \datavisualization [ + scientific axes=clean, + x axis={length=3cm, ticks=few}, + all axes={grid}, + visualize as smooth line + ] + data [format=function] { + var x : interval [-1.5:1.5] samples 7; + func y = \value x*\value x; + }; +\end{tikzpicture} +\end{codeexample} + +Section~\ref{section-dv-axes} explains in more detail how axes, ticks, and grid +lines can be chosen and configured. + + +\subsection{Concept: Visualizers} + +Data points and axes specify \emph{what} is visualized and \emph{where}. A +\emph{visualizer} specifies \emph{how} they are visualized. One of the most +common visualizers is a \emph{line visualizer} which connects the positions of +the data points in the plane using a line. Another common visualizer is the +\emph{scatter plot visualizer} where small marks are drawn at the positions of +the data points. More advanced visualizers include, say, box plot visualizers +or pie chart visualizers. +% +\begin{codeexample}[] +\begin{tikzpicture} + \datavisualization [ + scientific axes=clean, + x axis={length=3cm, ticks=few}, + visualize as smooth line + ] + data [format=function] { + var x : interval [-1.5:1.5] samples 7; + func y = \value x*\value x; + }; +\end{tikzpicture} +\end{codeexample} +% +\begin{codeexample}[] +\begin{tikzpicture} + \datavisualization [ + scientific axes=clean, + x axis={length=3cm, ticks=few}, + visualize as scatter + ] + data [format=function] { + var x : interval [-1.5:1.5] samples 7; + func y = \value x*\value x; + }; +\end{tikzpicture} +\end{codeexample} + +Section~\ref{section-dv-visualizers} provides more information on visualizers +as well as reference lists. + + +\subsection{Concept: Style Sheets and Legends} + +A single data visualizations may use more than one visualizer. For instance, if +you wish to create a plot containing several lines, a separate visualizer is +used for each line. In this case, two problems arise: +% +\begin{enumerate} + \item You may wish to make it easy for the reader to differentiate between + the different visualizers. For instance, one line should be black, + another should be red, and another blue. Alternatively, you might wish + one line to be solid, another to be dashed, and a third to be dotted. + + Specifying such styles is trickier than one might expect; experience + shows that many plots use ill-chosen and inconsistent styling. For this + reason, the data visualization introduces the notion of \emph{style + sheets} for visualizers and comes with some well-designed predefined + style sheets. + \item You may wish to add information concerning what the different + visualizers represent. This is typically done using a legend, but it is + even better to add labels directly inside the visualization. Both + approaches are supported. +\end{enumerate} + +An example where three functions are plotted and a legend is added is shown +below. Two style sheets are used so that \emph{both} the coloring and the +dashing is varied. +% +\begin{codeexample}[] +\begin{tikzpicture}[baseline] + \datavisualization [ scientific axes=clean, + y axis=grid, + visualize as smooth line/.list={sin,cos,tan}, + style sheet=strong colors, + style sheet=vary dashing, + sin={label in legend={text=$\sin x$}}, + cos={label in legend={text=$\cos x$}}, + tan={label in legend={text=$\tan x$}}, + data/format=function ] + data [set=sin] { + var x : interval [-0.5*pi:4]; + func y = sin(\value x r); + } + data [set=cos] { + var x : interval [-0.5*pi:4]; + func y = cos(\value x r); + } + data [set=tan] { + var x : interval [-0.3*pi:.3*pi]; + func y = tan(\value x r); + }; +\end{tikzpicture} +\end{codeexample} + +Section~\ref{section-dv-style-sheets} details style sheets and legends. + + +\subsection{Usage} +\label{section-dv-data-syntax} + +Inside a \tikzname\ picture you can use the |\datavisualization| command to +create a data visualization. You can use this command several times in a +picture to create pictures containing multiple data visualizations. + +\begin{command}{\datavisualization\opt{\oarg{data visualization options}}\meta{data specification}|;|} + This command is available only inside a |{tikzpicture}| environment. + + The \meta{data visualization options} are used to configure the data + visualization, that is, how the data is to be depicted. The options are + executed with the path prefix |/tikz/data visualization|. This means that + normal \tikzname\ options like |thin| or |red| cannot be used here. Rather, + a large number of options specific to data visualizations are available. + + As a minimum, you should specify at least two options: First, you should + use an option that selects an axis system that is appropriate for your + plot. Typical possible keys are |school book axes| or |scientific axes|, + detailed information on them can be found in Section~\ref{section-dv-axes}. + + Second, you use an option to select \emph{how} the data should be + visualized. This is done using a key like |visualize as line| which will, + as the name suggests, visualize the data by connecting data points in the + plane using a line. Similarly, |visualize as smooth cycle| will try to fit + a smooth cycle through the data points. Detailed information on possible + visualizers can be found in Section~\ref{section-dv-visualizers}. + + Following these options, the \meta{data specification} is used to provide + the actual to-be-visualized data. The syntax is somewhat similar to + commands like |\path|: The \meta{data specification} is a sequence of + keywords followed by local options and parameters, terminated with a + semicolon. (Indeed, like for the |\path| command, the \meta{data + visualizers options} need not be specified at the beginning, but additional + option surrounded by square brackets may be given anywhere inside the + \meta{data specification}.) + + The different possible keywords inside the \meta{data specification} are + explained in the following. +\end{command} + +\begin{datavisualizationoperation}{data}{\opt{\oarg{options}}\opt{\marg{inline data}}} + This command is used to specify data for the data visualization. It can be + used several times inside a single visualization and each time the + to-be-read data may have a different format, but the data will be + visualized as if it have been specified inside a single |data| command. + + The behaviour of the |data| command depends on whether the \meta{inline + data} is present. If it is not present, the \meta{options} must be used to + specify a source file from which the data is read; if the \meta{inline + data} is present no file will be used, instead the data should directly + reside inside the \TeX-file and be given between the curly braces + surrounding the \meta{inline data}. + + The \meta{options} are executed with the prefix |/pgf/data|. The following + options are always available: + % + \begin{key}{/pgf/data/read from file=\meta{filename} (initially \normalfont empty)} + If you set the |source| attribute to a non-empty \meta{filename}, the + data will be read from this file. In this case, no \meta{inline data} + may be present, not even empty curly braces should be provided. + % +\begin{codeexample}[code only] +\datavisualization ... + data [read from file=file1.csv] + data [read from file=file2.csv]; +\end{codeexample} + % + The other way round, if |read from file| is empty, the data must + directly follow as \meta{inline data}. + % +\begin{codeexample}[code only] +\datavisualization ... + data { + x, y + 1, 2 + 2, 3 + }; +\end{codeexample} + \end{key} + % + The second important key is |format|, which is used to specify the data + format: + % + \begin{key}{/pgf/data/format=\meta{format} (initially table)} + Use this key to locally set the format used for parsing the data, see + Section~\ref{section-dv-formats} for a list of predefined formats. + + The default format is the |table|-format, also known as + ``comma-separated values''. The first line contains names of attributes + separated by commas, all following lines constitute a data point where + the attributes are given by the comma-separated values in that line. + \end{key} + + + \medskip + \textbf{Presetting attributes.} + Normally, the inline data or the external data contains for each data point + the values of the different attributes. However, sometimes you may also + wish to set an attribute to a fixed value for all data points of a data + set. Suppose, for instance, that you have to source files + |experiment007.csv| and |experiment023.csv| and you would like that for all + data points of the first file the attribute |/data point/experiment id| is + set to 7 while for the data points of the second file they are set to 23. + In this case, you can specify the desired settings using an absolute path + inside the \meta{options}. The effect will be local to the current |data| + command: + % +\begin{codeexample}[code only] +\datavisualization... + data [/data point/experiment=7, read from file=experiment007.csv] + data [/data point/experiment=23, read from file=experiment023.csv]; +\end{codeexample} + +\begin{codeexample}[] +\tikz + \datavisualization [school book axes, visualize as line] + data [/data point/x=1] { + y + 1 + 2 + } + data [/data point/x=2] { + y + 2 + 0.5 + }; +\end{codeexample} + + + \medskip + \textbf{Setting options for multiple |data| commands.} + You may wish to generally set the format once and for all. This can be done + by using the following key: + % + \begin{stylekey}{/tikz/every data} + This key is executed for every |data| command. + \end{stylekey} + + Another way of passing options to multiple |data| commands is to use the + following facility: Whenever an option with the path + |/tikz/data visualization/data| is used, the path will be remapped to + |/pgf/data|. This means, in particular, that you can pass an option like + |data/format=table| to the |\datavisualization| command to set the data + format for all |data| commands of the data visualization. + + + \medskip + \textbf{Parsing inline data.} + When you specify data inline, \TeX\ needs to read the data + ``line-by-line'', while \TeX\ normally largely ignores end-of-line + characters. For this reason, the data visualization system temporarily + changes the meaning of the end-of-line character. This is only possible if + \TeX\ has not already processed the data in some other way (namely as the + parameter to some macro). + + The bottom line is that you cannot use inline data when the whole + |\datavisualization| command is passed as a parameter to some macro that is + not setup to handle ``fragile'' code. For instance, in a \textsc{beamer} + |frame| you need to add the |fragile| option when a data visualization + contains inline data. + + The problem does not arise when an external data |source| is specified. +\end{datavisualizationoperation} + +\begin{datavisualizationoperation}{data point}{\opt{\oarg{options}}} + This command is used to specify data a single data point. The + \meta{options} are simply executed with the path |/data point| and then a + data point is created. This means that inside the \meta{options} you just + specify the values of all attributes in key--value syntax. + % +\begin{codeexample}[] +\tikz \datavisualization [school book axes, visualize as line] + data point [x=1, y=1] data point [x=1, y=2] + data point [x=2, y=2] data point [x=2, y=0.5]; +\end{codeexample} + % +\end{datavisualizationoperation} + +\begin{key}{/tikz/data visualization/data point=\meta{options}} + This key is the ``key version'' of the previous command. The difference is + that this key can be used internally inside styles. + % +\begin{codeexample}[] +\tikzdatavisualizationset{ + horizontal/.style={ + data point={x=#1, y=1}, data point={x=#1, y=2}}, +} +\tikz \datavisualization +[ school book axes, visualize as line, + horizontal=1, + horizontal=2 ]; +\end{codeexample} + % +\end{key} + +\begin{datavisualizationoperation}{data group}{\opt{\oarg{options}}\marg{name}\opt{|+=|\marg{data specifications}}} + You can store a whole \meta{data specification} in a \emph{data group}. + This allows you to reuse data in multiple places without having to write + the data to an external file. + + The syntax of this command comes in the following three variants: + % + \begin{itemize} + \item |data group| \opt{\oarg{options}} \marg{name} |=| \marg{data + specifications} + \item |data group| \opt{\oarg{options}} \marg{name} |+=| \marg{data + specifications} + \item |data group| \opt{\oarg{options}} \marg{name} + \end{itemize} + % + In the first case, a new data group called \meta{name} is created (an + existing data group of the same name will be erased) and the following + \meta{data specifications} is stored in this data group. The data group + will not be fed to the rendering pipeline, but it is parsed at this point + as if it were. The defined data group is defined globally, so you can used + it in subsequent visualizations. The \meta{options} are saved with the + parsed \meta{data specifications}. + + In the second case, an already existing data group is extended by adding + the \meta{data specifications} to it. + + In the third case (detected by noting that the \meta{name} is neither + followed by an equal sign nor a plus sign), the contents of the previously + defined data group \meta{name} is inserted. The \meta{options} are also + executed. + + Let is now first create a data group. Note that nothing is drawn since the + ``dummy'' data visualization is empty and used only for the definition of + the data group. + % +\begin{codeexample}[] +\tikz \datavisualization data group {points} = { + data { + x, y + 0, 1 + 1, 2 + 2, 2 + 5, 1 + 2, 0 + 1, 1 + } +}; +\end{codeexample} + + We can now use this data in different plots: + % +\begin{codeexample}[] +\tikz \datavisualization [school book axes, visualize as line] data group {points}; +\qquad +\tikz \datavisualization [scientific axes=clean, visualize as line] data group {points}; +\end{codeexample} + % +\end{datavisualizationoperation} + +\begin{datavisualizationoperation}{scope}{\opt{\oarg{options}}\marg{data specification}} + Scopes can be used to nest hierarchical data sets. The \meta{options} will + be executed with the path |/pgf/data| and will only apply to the data sets + specified inside the \meta{data specification}, which may contain |data| or + |scope| commands once more: + % +\begin{codeexample}[code only] +\datavisualization... + scope [/data point/experiment=7] + { + data [read from file=experiment007-part1.csv] + data [read from file=experiment007-part2.csv] + data [read from file=experiment007-part3.csv] + } + scope [/data point/experiment=23, format=foo] + { + data [read from file=experiment023-part1.foo] + data [read from file=experiment023-part2.foo] + }; +\end{codeexample} + % +\end{datavisualizationoperation} + +\begin{datavisualizationoperation}{info}{\opt{\oarg{options}}\marg{code}} + This command will execute normal \tikzname\ \meta{code} at the end of a + data visualization. The \meta{options} are executed with the normal path + |/tikz/|. + + The only difference between this command and just giving the \meta{code} + directly following the data visualization is that inside the \meta{code} + following an |info| command you still have access to the coordinate system + of the data visualization. In sharp contrast, \tikzname\ code given after a + data visualization can no longer access this coordinate system. + % +\begin{codeexample}[] +\begin{tikzpicture}[baseline] + \datavisualization [ school book axes, visualize as line ] + data [format=function] { + var x : interval [-0.1*pi:2]; + func y = sin(\value x r); + } + info { + \draw [red] (visualization cs: x={(.5*pi)}, y=1) circle [radius=1pt] + node [above,font=\footnotesize] {extremal point}; + }; +\end{tikzpicture} +\end{codeexample} + + As can be seen, inside a data visualization a special coordinate system is + available: + + \begin{coordinatesystem}{visualization} + As for other coordinate systems, the syntax is + \declare{|(visualization cs:|\meta{list of attribute-value pairs}|)|}. + The effect is the following: For each pair + \meta{attribute}|=|\meta{value} in the \meta{list} the key + |/data point/|\meta{attribute} is set to \meta{value}. Then, it is + computed where the resulting data point ``would lie'' on the canvas + (however, no data point is passed to the visualizers). + \end{coordinatesystem} +\end{datavisualizationoperation} + +\begin{datavisualizationoperation}{info'}{\opt{\oarg{options}}\marg{code}} + This command works like |info|, only the \meta{code} will be executed just + before the visualization is done. This allows you to draw things + \emph{behind} the visualization. + % +\begin{codeexample}[] +\begin{tikzpicture}[baseline] + \datavisualization [ school book axes, visualize as line ] + data [format=function] { + var x : interval [-0.1*pi:2]; + func y = sin(\value x r); + } + info' { + \fill [red] (visualization cs: x={(.5*pi)}, y=1) circle [radius=2mm]; + }; +\end{tikzpicture} +\end{codeexample} + % +\end{datavisualizationoperation} + +\label{section-dv-bounding-box}% +\begin{predefinednode}{data visualization bounding box} + This rectangle node stores a bounding box of the data visualization that is + currently being constructed. This node can be useful inside |info| commands + or when labels need to be added. +\end{predefinednode} + +\begin{predefinednode}{data bounding box} + This rectangle node is similar to |data visualization bounding box|, but it + keeps track only of the actual data. The spaces needed for grid lines, + ticks, axis labels, tick labels, and other all other information that is + not part of the actual data is not part of this box. +\end{predefinednode} + + +\subsection{Advanced: Executing User Code During a Data Visualization} +\label{section-dv-user-code} + +The following keys can be passed to the |\datavisualization| command and allow +you to execute some code at some special time during the data visualization +process. For details of the process and on which signals are emitted when, see +Section~\ref{section-dv-backend}. + +\begin{key}{/tikz/data visualization/before survey=\meta{code}} + The \meta{code} is passed to the |before survey| method of the data + visualization object and then executed at the appropriate time (see + Section~\ref{section-dv-backend} for details). + + The following commands work likewise: +\end{key} +% +\begin{key}{/tikz/data visualization/at start survey=\meta{code}} +\end{key} +% +\begin{key}{/tikz/data visualization/at end survey=\meta{code}} +\end{key} +% +\begin{key}{/tikz/data visualization/after survey=\meta{code}} +\end{key} +% +\begin{key}{/tikz/data visualization/before visualization=\meta{code}} +\end{key} +% +\begin{key}{/tikz/data visualization/at start visualization=\meta{code}} +\end{key} +% +\begin{key}{/tikz/data visualization/at end visualization=\meta{code}} +\end{key} +% +\begin{key}{/tikz/data visualization/after visualization=\meta{code}} +\end{key} + + +\subsection{Advanced: Creating New Objects} + +You will need the following key only when you wish to create new rendering +pipelines from scratch -- instead of modifying an existing pipeline as you +would normally do. In the following it is assumed that you are familiar with +the concepts of Section~\ref{section-dv-backend}. + +\begin{key}{/tikz/data visualization/new object=\meta{options}} + This key serves two purposes: + % + \begin{enumerate} + \item This method makes it easy to create a new object as part of the + rendering pipeline, using \meta{options} to specify arguments + rather that directly calling |\pgfoonew|. Since you have the full + power of the keys mechanism at your disposal, it is easy, for + instance, to control whether or not parameters to the constructor + are expanded or not. + \item The object is not created immediately, but only just before the + visualization starts. This allows you to specify that an object + must be created, but the parameter values of for its constructor + may depend on keys that are not yet set. A typical application is + the creating of an axis object: When you say |scientific axes|, the + |new object| command is used internally to create two objects + representing these axes. However, keys like |x={length=5cm}| can + only \emph{later} be used to specify the parameters that need to be + passed to the constructor of the objects. + \end{enumerate} + + The following keys may be used inside the \meta{options}: + % + \begin{key}{/tikz/data visualization/class=\meta{class name}} + The class of the to-be-created object. + \end{key} + % + \begin{key}{/tikz/data visualization/when=\meta{phase name} (initially before survey)} + This key is used to specify when the object is to be created. As + described above, the object is not created immediately, but at some + time during the rendering process. You can specify any of the phases + defined by the data visualization object, see + Section~\ref{section-dv-backend} for details. + \end{key} + % + \begin{key}{/tikz/data visualization/store=\meta{key name}} + If the \meta{key name} is not empty, once the object has been created, + a handle to the object will be stored in \meta{key name}. If a handle + is already stored in \meta{key name}, the object is not created twice. + \end{key} + % + \begin{key}{/tikz/data visualization/before creation=\meta{code}} + This code is executed right before the object is finally created. It + can be used to compute values that are then passed to the constructor. + \end{key} + % + \begin{key}{/tikz/data visualization/after creation=\meta{code}} + This code is executed right after the object has just been created. A + handle to the just-created object is available in |\tikzdvobj|. + \end{key} + % + \begin{key}{/tikz/data visualization/arg1=\meta{value}} + The value to be passed as the first parameter to the constructor. + Similarly, the keys |arg2| to |arg8| specify further parameters passed. + Naturally, only as many arguments are passed as parameters are set. + Here is an example: + % +\begin{codeexample}[code only] +\tikzdatavisualizationset{ + new object={ + class = example class, + arg1 = foo, + arg2 = \bar + } +} +\end{codeexample} + % + causes the following object creation code to be executed later on: + % +\begin{codeexample}[code only] +\pgfoonew \tikzdvobj=new example class(foo,\bar) +\end{codeexample} + % + Note that you key mechanisms like |.expand once| to pass the value of a + macro instead of the macro itself: + % +\begin{codeexample}[code only] +\tikzdatavisualizationset{ + new object={ + class = example class, + arg1 = foo, + arg2/.expand once = \bar + } +} +\end{codeexample} + % + Now, if |\bar| is set to |This \emph{is} it.|\@ at the moment to object + is created later on, the following object creation code is executed: + % +\begin{codeexample}[code only] +\pgfoonew \tikzdvobj=new example class(foo,This \emph{is} it) +\end{codeexample} + \end{key} + + \begin{key}{/tikz/data visualization/arg1 from key=\meta{key}} + Works like the |arg1|, only the value that is passed to the constructor + is the current value of the specified \meta{key} at the moment when the + object is created. + % +\begin{codeexample}[code only] +\tikzdatavisualizationset{ + new object={ + class = example class, + arg1 from key = /tikz/some key + } +} +\tikzset{some key/.initial=foobar} +\end{codeexample} + % + causes the following to be executed: + % +\begin{codeexample}[code only] +\pgfoonew \tikzdvobj=new example class(foobar) +\end{codeexample} + % + Naturally, the keys |arg2 from key| to |arg8 from key| are also + provided. + \end{key} + + \begin{key}{/tikz/data visualization/arg1 handle from key=\meta{key}} + Works like the |arg1 from key|, only the key must store an object and + instead of the object a handle to the object is passed to the + constructor. + \end{key} +\end{key} |