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+% Copyright 2019 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{Spy Library: Magnifying Parts of Pictures}
+\label{section-library-spy}
+
+\begin{tikzlibrary}{spy}
+ The package defines options for creating pictures in which some part of the
+ picture is repeated in another area in a magnified way (as if you were
+ looking through a spyglass, hence the name).
+\end{tikzlibrary}
+
+
+\subsection{Magnifying a Part of a Picture}
+
+The idea behind the |spy| library is to make it easy to create high-density
+pictures in which some important parts are repeated somewhere, but magnified as
+if you were looking through a spyglass:
+%
+\begin{codeexample}[preamble={\usetikzlibrary{decorations.fractals,spy}}]
+\begin{tikzpicture}
+ [spy using outlines={circle, magnification=4, size=2cm, connect spies}]
+
+ \draw [help lines] (0,0) grid (3,2);
+
+ \draw [decoration=Koch curve type 1]
+ decorate { decorate{ decorate{ decorate{ (0,0) -- (2,0) }}}};
+
+ \spy [red] on (1.6,0.3)
+ in node [left] at (3.5,-1.25);
+
+ \spy [blue, size=1cm] on (1,1)
+ in node [right] at (0,-1.25);
+\end{tikzpicture}
+\end{codeexample}
+
+\begin{codeexample}[preamble={\usetikzlibrary{decorations.fractals,spy}}]
+\begin{tikzpicture}[spy using overlays={size=12mm}]
+ \draw [decoration=Koch snowflake]
+ decorate { decorate{ decorate{ decorate{ (0,0) -- (2,0) }}}};
+
+ \spy [green,magnification=3] on (0.6,0.1) in node at (-0.3,-1);
+ \spy [blue,magnification=5] on (1,0.5) in node at (1,-1);
+ \spy [red,magnification=10] on (1.6,0.1) in node at (2.3,-1);
+\end{tikzpicture}
+\end{codeexample}
+
+Note that this magnification uses what is called a \emph{canvas transformation}
+in this manual: Everything is magnified, including line width and text.
+
+In order for ``spying'' to work, the picture obviously has to be drawn several
+times: Once at its normal size and then again for each ``magnifying glass''.
+Several keys and commands work in concert to make this possible:
+%
+\begin{itemize}
+ \item You need to make \tikzname\ aware of the fact that a picture (or just
+ a scope) is to be magnified. This is done by adding the special key
+ |spy scope| to a |{scope}| or |{tikzpicture}| (which is also just a
+ scope). Some special keys like |spy using outlines| implicitly set the
+ |spy scope|.
+ \item Inside this scope you may then use the command |\spy|, which is only
+ available inside such scopes (so there is no danger of you
+ inadvertently using this command outside such a scope). This command
+ has a special syntax and will (at some point) create two nodes: One
+ node that shows the magnified picture (called the \emph{spy-in node})
+ and another node showing which part of the original picture is
+ magnified (called the \emph{spy-on} node). The spy-in node is, indeed,
+ a normal node, so it can have any shape or border that you like and you
+ can apply all of \tikzname's advanced features to it. The only
+ difference compared to a normal node is that instead of some ``text''
+ it contains a magnified version of the picture, clipped to the size of
+ the node.
+
+ The |\spy| command does not create the nodes immediately. Rather, the
+ creation of these nodes is postponed till the end of the |spy scope| in
+ which the |\spy| command is used. This is necessary since in order to
+ repeat the whole scope inside the node containing the magnified
+ version, the whole picture needs to be available when this node is
+ created.
+\end{itemize}
+
+A basic question any library for ``magnifying things'' has to address is how
+you specify which part of the picture is to be magnified (the spy-on node) and
+where this magnified part is to be shown (the spy-in node). There are two
+possible ways:
+%
+\begin{enumerate}
+ \item You specify the size and position of the spy-on node. Then the size
+ of the spy-in node is determined by the size of the spy-on node and the
+ magnification factor -- you can still decide where the spy-in node
+ should be placed, but not its size.
+ \item Alternatively, you specify the size and position of the spy-in node.
+ Then, similarly to the first case, the size of the spy-on node is
+ determined implicitly and you can only decide where the spy-on node
+ should be placed, but not its size.
+\end{enumerate}
+
+The |spy| library uses the second method: You specify the size and position of
+the spy-in nodes, the sizes of the spy-on nodes are then computed
+automatically.
+
+
+\subsection{Spy Scopes}
+
+\begin{key}{/tikz/spy scope=\meta{options} (default \normalfont empty)}
+ This option may be used with a |{scope}| or any environment that creates
+ such a scope internally (like |{tikzpicture}|). It has the following
+ effects:
+ %
+ \begin{itemize}
+ \item It resets a number of graphic state parameters, including the
+ color, line style, and others. This is necessary for technical
+ reasons.
+ \item It tells \tikzname\ that the content of the scope should be saved
+ internally in a special box.
+ \item It defines the command |\spy| so that it can be used inside the
+ scope.
+ \item At the end of the scope, the nodes belonging to the |\spy|
+ commands used inside the scope are created.
+ \item The \meta{options} are saved in an internal style. Each time
+ |\spy| is used, these \meta{options} will be used.
+ \item Three keys are defined that provide useful shortcuts:
+ %
+ \begin{key}{/tikz/size=\meta{dimension}}
+ Inside a |spy scope|, this is a shortcut for |minimum size|.
+ \end{key}
+ %
+ \begin{key}{/tikz/height=\meta{dimension}}
+ Inside a |spy scope|, this is a shortcut for |minimum height|.
+ \end{key}
+ %
+ \begin{key}{/tikz/width=\meta{dimension}}
+ Inside a |spy scope|, this is a shortcut for |minimum width|.
+ \end{key}
+ \end{itemize}
+ %
+ It is permissible to nest |spy scopes|. In this case, all |\spy| commands
+ inside the inner |spy scope| only have an effect on material inside the
+ scope, whereas |\spy| commands outside the inner |spy scope| but inside the
+ outer |spy scope| allow you to ``spy on the spy''.
+ %
+\begin{codeexample}[preamble={\usetikzlibrary{decorations.fractals,spy}}]
+\begin{tikzpicture}
+ [spy using outlines={rectangle, red, magnification=5,
+ size=1.5cm, connect spies}]
+
+ \begin{scope}
+ [spy using outlines={circle, blue,
+ magnification=3, size=1.5cm, connect spies}]
+ \draw [help lines] (0,0) grid (3,2);
+
+ \draw [decoration=Koch curve type 1]
+ decorate{ decorate{ decorate{ (0,0) -- (2,0) }}};
+
+ \spy on (1.6,0.3) in node (zoom) [left] at (3.5,-1.25);
+ \end{scope}
+
+ \spy on (zoom.north west) in node [right] at (0,-1.25);
+\end{tikzpicture}
+\end{codeexample}
+ %
+\end{key}
+
+
+\subsection{The Spy Command}
+
+\begin{command}{\spy \opt{\oarg{options}} |on| \meta{coordinate} \texttt{in node} \meta{node options}|;|}
+ This command can only be used inside a |spy scope|. Let us start with the
+ syntax:
+ %
+ \begin{itemize}
+ \item The |\spy| command is not a special case of |\path|. Rather, it
+ has a small parser of its own.
+ \item Following the optional \meta{options}, you must write |on|,
+ followed by a coordinate. This coordinate will be the center of the
+ area that is to be magnified.
+ \item Following the \meta{coordinate}, you must write |in node|
+ followed by some \meta{node options}. The syntax for these options
+ is the same as for a normal |node| path command, such as |[left]|
+ or |(foo) [red] at (bar)|. \emph{However}, \meta{node options} are
+ \emph{not} followed by a curly brace. Rather, the \meta{node
+ options} must directly be followed by a semicolon.
+ \end{itemize}
+ %
+ The effect of this command is the following: The \meta{options},
+ \meta{coordinate}, and \meta{node options} are stored internally till the
+ end of the current |spy scope|. This means that, in particular, you can
+ reference any node inside the |spy scope|, even if it is not yet defined
+ when the |\spy| command is given. At the end of the current |spy scope|,
+ two nodes are created, called the \emph{spy-in node} and the \emph{spy-on
+ node}.
+ %
+ \begin{itemize}
+ \item The \emph{spy-in node} is the node that contains a magnified part
+ of the picture (the node \emph{in} which we see on what we spy).
+ This node is, indeed, a normal \tikzname\ node, so you can use all
+ standard options to style this node. In particular, you can specify
+ a shape or a border color or a drop shadow or whatever. The only
+ thing that is special about this node is that instead of containing
+ some normal text, its ``text'' is the magnified picture.
+
+ To be precise, the picture of the |spy scope| is scaled by a
+ certain factor, specified by the |lens| or |magnification| options
+ discussed below, and is shifted in such a way that the
+ \meta{coordinate} lies at the center of the spy-on node.
+ \item The \emph{spy-on node} is a node that is centered on the
+ \meta{coordinate} and whose size reflects exactly the area shown
+ inside the spy-in node (the node containing \emph{on} what we spy).
+ \end{itemize}
+
+ Let us now go over what happens in detail when the two nodes are
+ created:
+ %
+ \begin{enumerate}
+ \item A scope is started. Two sets of options are used with this scope:
+ First, the options passed to the enclosing |spy scope| and then the
+ \meta{options} (which will, thus, overrule the options of the
+ |spy scope|).
+ \item Then, the spy-on node is created. However, we will first discuss
+ the spy-in node.
+ \item The spy-in node is created after the spy-on node (and, hence,
+ will cover the spy-on node in case they overlap). When this node is
+ created, the \meta{node options} are used in addition to the effect
+ caused by the \meta{options} and the options of the |{spy scope}|.
+ Additionally, the following style is used:
+ %
+ \begin{stylekey}{/tikz/every spy in node}
+ This style is used with every spy-in node.
+ \end{stylekey}
+ %
+ The position of the node (the |at| option) is set to the
+ \meta{coordinate} by default, so that it will cover the
+ to-be-magnified area. You can change this by providing the |at|
+ option yourself:
+ %
+\begin{codeexample}[preamble={\usetikzlibrary{decorations.fractals,spy}}]
+\begin{tikzpicture}
+ [spy using outlines={circle, magnification=3, size=1cm}]
+
+ \draw [decoration=Koch curve type 1]
+ decorate{ decorate{ decorate{ (0,0) -- (2,0) }}};
+
+ \spy [red] on (1.6,0.3) in node;
+ \spy [blue] on (1,1) in node at (1,-1);
+\end{tikzpicture}
+\end{codeexample}
+ %
+ No ``text'' can be specified for the node. Rather, the ``text''
+ shown inside this node is the picture of the current |spy scope|,
+ but canvas-transformed according to the following key:
+ %
+ \begin{key}{/tikz/lens=\meta{options}}
+ The \meta{options} should contain transformation commands like
+ |scale| or |rotate|. These transformations are applied to the
+ picture when it is shown inside the spy-on node.
+ \end{key}
+ %
+ Since the most common transformation is undoubtedly a simple
+ scaling, there is a special style for this:
+ %
+ \begin{key}{/tikz/magnification=\meta{number}}
+ This has the same effect as saying
+ |lens={scale=|\meta{number}|}|.
+ \end{key}
+ %
+ Now, usually the size of a node is determined in such a way that it
+ ``fits'' around the text of the node. For a spy-on node this is not
+ a good approach since the ``text'' of this node would contain ``the
+ whole picture''. Because of this, \tikzname\ acts as if the
+ ``text'' of the node has zero size. You must then use keys like
+ |minimum size| to cause the node to have a certain size. Note that
+ the key |size| is an abbreviation for |minimum size| inside a spy
+ scope.
+
+ You can name the spy-on node in the usual ways. Additionally, the
+ node is (also) always named |tikzspyinnode|. Following the spy
+ scope, you can use this node like any other node:
+ %
+\begin{codeexample}[preamble={\usetikzlibrary{decorations.fractals,spy}}]
+\begin{tikzpicture}
+ \begin{scope}
+ [spy using outlines={circle, magnification=3, size=2cm, connect spies}]
+
+ \draw [decoration=Koch curve type 1]
+ decorate{ decorate{ decorate{ (0,0) -- (2,0) }}};
+
+ \spy [red] on (1.6,0.3) in node (a) [left] at (3.5,-1.25);
+
+ \spy [blue, size=1cm] on (1,1) in node (b) [right] at (0,-1.25);
+ \end{scope}
+ \draw [ultra thick, green!50!black] (b) -- (a.north west);
+\end{tikzpicture}
+\end{codeexample}
+ %
+ \item Once both nodes have been created, the current value of the
+ following key is used to connect them:
+ %
+ \begin{key}{/tikz/spy connection path=\meta{code} (initially \normalfont empty)}
+ The \meta{code} is executed after the spy-on and spy-in nodes
+ have just been created. Inside this \meta{code}, the two nodes
+ can be accessed as |tikzspyinnode| and |tikzspyonnode|. For
+ example, the key |connect spies| sets this command to
+ %
+\begin{codeexample}[code only]
+\draw[thin] (tikzspyonnode) -- (tikzspyinnode);
+\end{codeexample}
+ \end{key}
+ \end{enumerate}
+ %
+ Returning to the creation of the spy-in node: This node is centered on
+ \meta{coordinate} (more precisely, its anchor is set to |center| and the
+ |at| option is set to \meta{coordinate}). Its size and shape are initially
+ determined in the same way as the size and shape of the spy-on node
+ (unless, of course, you explicitly provide a different shape for, say, the
+ spy-on node locally, which is not really a good idea). Then, additionally,
+ the \emph{inverted} transformation done by the |lens| option is applied,
+ resulting in a node whose size and shape exactly corresponds to the area in
+ the picture that is shown in the spy-on node.
+ %
+\begin{codeexample}[preamble={\usetikzlibrary{decorations.fractals,spy}}]
+\begin{tikzpicture}
+ [spy using outlines={lens={scale=3,rotate=20}, size=2cm, connect spies}]
+
+ \draw [decoration=Koch curve type 1]
+ decorate{ decorate{ decorate{ (0,0) -- (2,0) }}};
+
+ \spy [red] on (1.6,0.3) in node at (2.5,-1.25);
+\end{tikzpicture}
+\end{codeexample}
+
+ Like for the spy-in node, a style can be used to format the spy-on node:
+ %
+ \begin{stylekey}{/tikz/every spy on node}
+ This style is used with every spy-on node.
+ \end{stylekey}
+ %
+ The spy-on node is named |tikzspyonnode| (but, as always, this node is only
+ available after the spy scope). If you have multiple spy-on nodes and you
+ would like to access all of them, you need to use the |name| key inside the
+ |every spy on node| style.
+
+ The |inner sep| and |outer sep| of both spy-in and spy-on nodes are set to
+ |0pt|.
+\end{command}
+
+
+\subsection{Predefined Spy Styles}
+
+There are some predefined styles that make using the |spy| library easier. The
+following two styles can be used instead of |spy scope|, they pass their
+\meta{options} directly to |spy scope|. They additionally set up the graphic
+styles to be used for the spy-in nodes and the spy-on nodes in some special
+way.
+
+\begin{key}{/tikz/spy using outlines=\meta{options} (default \normalfont empty)}
+ This key creates a |spy scope| in which the spy-in node is drawn, but not
+ filled, using a thick line; and the spy-on node is drawn, but not filled,
+ using a very thin line.
+ %
+\begin{codeexample}[preamble={\usetikzlibrary{decorations.fractals,spy}}]
+\begin{tikzpicture}
+ [spy using outlines={circle, magnification=3, size=1cm, connect spies}]
+
+ \draw [decoration=Koch curve type 1]
+ decorate{ decorate{ decorate{ (0,0) -- (2,0) }}};
+
+ \spy [red] on (1.6,0.3) in node at (3,1);
+\end{tikzpicture}
+\end{codeexample}
+ %
+\end{key}
+
+\begin{key}{/tikz/spy using overlays=\meta{options} (default \normalfont empty)}
+ This key creates a |spy scope| in which both the spy-in and spy-on nodes
+ are filled, but with the fill opacity set to 20\%.
+ %
+\begin{codeexample}[preamble={\usetikzlibrary{decorations.fractals,spy}}]
+\begin{tikzpicture}
+ [spy using overlays={circle, magnification=3, size=1cm, connect spies}]
+
+ \draw [decoration=Koch curve type 1]
+ decorate{ decorate{ decorate{ (0,0) -- (2,0) }}};
+
+ \spy [green] on (1.6,0.3) in node at (3,1);
+\end{tikzpicture}
+\end{codeexample}
+ %
+\end{key}
+
+The following style is useful for connecting the spy-in and the spy-on nodes:
+
+\begin{key}{/tikz/connect spies}
+ Causes the spy-in and the spy-on nodes to be connected by a thin line.
+ %
+\begin{codeexample}[preamble={\usetikzlibrary{decorations.fractals,spy}}]
+\begin{tikzpicture}
+ [spy using overlays={circle, magnification=3, size=1cm}]
+
+ \draw [decoration=Koch curve type 2]
+ decorate{ decorate{ decorate{ (0,0) -- (2,0) }}};
+
+ \spy [green] on (1.6,0.1) in node at (3,1);
+ \spy [red,connect spies] on (0.5,0.4) in node at (1,1.5);
+\end{tikzpicture}
+\end{codeexample}
+ %
+\end{key}
+
+
+\subsection{Examples}
+
+Usually, the spy-in node and the spy-on node should have the same shape.
+However, you might also wish to use the |circle| shape for the spy-on node and
+the |magnifying glass| shape for the spy-in node:
+%
+\begin{codeexample}[preamble={\usetikzlibrary{decorations.fractals,shadows,shapes.symbols,spy}}]
+\tikzset{spy using mag glass/.style={
+ spy scope={
+ every spy on node/.style={
+ circle,
+ fill, fill opacity=0.2, text opacity=1},
+ every spy in node/.style={
+ magnifying glass, circular drop shadow,
+ fill=white, draw, ultra thick, cap=round},
+ #1
+ }}}
+\begin{tikzpicture}[spy using mag glass={magnification=3, size=1cm}]
+ \draw [decoration=Koch curve type 2]
+ decorate{ decorate{ decorate{ (0,0) -- (2,0) }}};
+
+ \spy [green!50!black] on (1.6,0.1) in node at (2.5,-0.5);
+\end{tikzpicture}
+\end{codeexample}
+
+With the magnifying glass, you can also put it ``on top'' of the picture
+itself:
+%
+\begin{codeexample}[preamble={\usetikzlibrary{decorations.fractals,shadows,shapes.symbols,spy}}]
+\begin{tikzpicture}
+ [spy scope={magnification=4, size=1cm},
+ every spy in node/.style={
+ magnifying glass, circular drop shadow,
+ fill=white, draw, ultra thick, cap=round}]
+
+ \draw [decoration=Koch curve type 2]
+ decorate{ decorate{ decorate{ (0,0) -- (2,0) }}};
+
+ \spy on (1.6,0.1) in node;
+\end{tikzpicture}
+\end{codeexample}
+
+
+%%% Local Variables:
+%%% mode: latex
+%%% TeX-master: "pgfmanual-pdftex-version"
+%%% End: