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diff --git a/graphics/pgf/base/doc/pgfmanual-en-tikz-pics.tex b/graphics/pgf/base/doc/pgfmanual-en-tikz-pics.tex new file mode 100644 index 0000000000..e24c1cee9f --- /dev/null +++ b/graphics/pgf/base/doc/pgfmanual-en-tikz-pics.tex @@ -0,0 +1,645 @@ +% 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{Pics: Small Pictures on Paths} +\label{section-pics} + +\subsection{Overview} + +A ``pic'' is a ``short picture'' (hence the short name\dots) that can be +inserted anywhere in \tikzname\ picture where you could also insert a node. +Similarly to nodes, pics have a ``shape'' (called \emph{type} to avoid +confusion) that someone has defined. Each time a pic of a specified type is +used, the type's code is executed, resulting in some drawings to be added to +the current picture. The syntax for adding nodes and adding pics to a picture +are also very similar. The core difference is that pics are typically more +complex than nodes and may consist of a whole bunch of nodes themselves +together with complex paths joining them. + +As a very simple example, suppose we want to define a pic type |seagull| that +just draw ``two bumps''. The code for this definition is quite easy: +% +\begin{codeexample}[code only] +\tikzset{ + seagull/.pic={ + % Code for a "seagull". Do you see it?... + \draw (-3mm,0) to [bend left] (0,0) to [bend left] (3mm,0); + } +} +\end{codeexample} + +The first line just tells \TeX\ that you set some \tikzname\ options for the +current scope (which is the whole document); you could put |seagull/.pic=...| +anywhere else where \tikzname\ options are allowed (which is just about +anywhere). We have now defined a |seagull| pic type and can use it as follows: +% +\tikzset{ + seagull/.pic={ + % Code for a "seagull". Do you see it?... + \draw (-3mm,0) to [bend left] (0,0) to [bend left] (3mm,0); + } +} +\begin{codeexample}[ + pre={\tikzset{ + seagull/.pic={ + % Code for a "seagull". Do you see it?... + \draw (-3mm,0) to [bend left] (0,0) to [bend left] (3mm,0); + }, +}}] +\tikz \fill [fill=blue!20] + (1,1) + -- (2,2) pic {seagull} + -- (3,2) pic {seagull} + -- (3,1) pic [rotate=30] {seagull} + -- (2,1) pic [red] {seagull}; +\end{codeexample} + +As can be see, defining new types of pics is much easier than defining new +shapes for nodes; but see Section~\ref{section-new-pic-types} for the fine +details. + +Since defining new pics types is easier than defining new node shapes and since +using pics is as easy as using nodes, why should you use nodes at all? There +are chiefly two reasons: +% +\begin{enumerate} + \item Unlike nodes, pics cannot be referenced later on. You \emph{can} + reference nodes that are inside a pic, but not ``the pic itself''. In + particular, you cannot draw lines between pics the way you can draw + them between nodes. In general, whenever it makes sense that some + drawing could conceivably be connected to other node-like-things, then + a node is better than a pic. + \item If pics are used to emulate the full power of a node (which is + possible, in principle), they will be slower to construct and take up + more memory than a node achieving the same effect. +\end{enumerate} + +Despite these drawbacks, pics are an excellent choice for creating highly +configurable reusable pieces of drawings that can be inserted into larger +contexts. + + +\subsection{The Pic Syntax} + +\begin{command}{\pic} + Inside |{tikzpicture}| this is an abbreviation for |\path pic|. +\end{command} + +The syntax for adding a pic to a picture is very similar to the syntax used for +nodes (indeed, internally the same parser code is used). The main difference is +that instead of a node contents you provide the picture's type between the +braces: + +\begin{pathoperation}{pic}{ + \opt{\meta{foreach statements}} + \opt{|[|\meta{options}|]|} + \opt{|(|\meta{prefix}|)|} + \opt{|at(|\meta{coordinate}|)|} + \opt{|:|\meta{animation attribute}|=|\marg{options}} + \opt{\marg{pic type}}% +} + Adds a pic to the current \tikzname\ picture of the specified \meta{pic + type}. The effect is, basically, that some code associated with the + \meta{pic type} is executed (how this works, exactly, is explained later). + This code can consist of arbitrary \tikzname\ code. As for nodes, the + current path will not be modified by this path command, all drawings + produced by the code are ``external'' to the path the same way neither a + node nor its border are part of the path on which they are specified. + + Just like the |node| command, this path operation is somewhat complex and + we go over it step by step. + + \medskip + \textbf{Order of the parts of the specification.} + Just like for nodes, everything between ``|pic|'' and the opening brace of + the \meta{pic type} is optional and can be given in any order. If there are + \meta{foreach statements}, they must come first, directly following + ``|pic|''. As for nodes, the ``end'' of the pic specification is normally + detected by the presence of the opening brace. You can, however, use the + |pic type| option to specify the pic type as an option. + + \begin{key}{/tikz/pic type=\meta{pic type}} + This key sets the pic type of the current~|pic|. When this option is + used inside an option block of a |pic|, the parsing of the |pic| ends + immediately and no pic type in braces is expected. (In other words, + this option behaves exactly like the |node contents| option and, + indeed, the two are interchangeable.) + % +\begin{codeexample}[ + pre={\tikzset{ + seagull/.pic={ + % Code for a "seagull". Do you see it?... + \draw (-3mm,0) to [bend left] (0,0) to [bend left] (3mm,0); + }, +}}] +\tikz { + \path (0,0) pic [pic type = seagull] + (1,0) pic {seagull}; +} +\end{codeexample} + \end{key} + + \medskip + \textbf{The location of a pic.} + Just like nodes, pics are placed at the last position mentioned on the path + or, when |at| is used, at a specified position. ``Placing'' a pic somewhere + actually means that the coordinate system is translated (shifted) to this + last position. This means that inside of the pic type's code any mentioning + of the origin refers to the last position used on the path or to the + specified |at|. + % +\begin{codeexample}[ + pre={\tikzset{ + seagull/.pic={ + % Code for a "seagull". Do you see it?... + \draw (-3mm,0) to [bend left] (0,0) to [bend left] (3mm,0); + }, +}}] +\tikz { % different ways of placing pics + \draw [help lines] (0,0) grid (3,2); + \pic at (1,0) {seagull}; + \path (2,1) pic {seagull}; + \pic [at={(3,2)}] {seagull}; +} +\end{codeexample} + + As for nodes, except for the described shifting, the coordinate system of a + pic is reset prior to executing the pic type's code. This can be changed + using the |transform shape| option, which has the same effect as for nodes: + The ``outer'' transformation gets applied to the node: + % +\begin{codeexample}[ + pre={\tikzset{ + seagull/.pic={ + % Code for a "seagull". Do you see it?... + \draw (-3mm,0) to [bend left] (0,0) to [bend left] (3mm,0); + }, +}}] +\tikz [scale=2] { + \pic at (0,0) {seagull}; + \pic at (1,0) [transform shape] {seagull}; +} +\end{codeexample} + + When the \meta{options} contain transformation commands like |scale| or + |rotate|, these transformations always apply to the pic: + % +\begin{codeexample}[ + pre={\tikzset{ + seagull/.pic={ + % Code for a "seagull". Do you see it?... + \draw (-3mm,0) to [bend left] (0,0) to [bend left] (3mm,0); + }, +}}] +\tikz [rotate=30] { + \pic at (0,0) {seagull}; + \pic at (1,0) [rotate=90] {seagull}; +} +\end{codeexample} + + Just like nodes, pics can also be positioned implicitly and, somewhat + unsurprisingly, the same rules concerning positioning and sloping apply: + % +\begin{codeexample}[ + pre={\tikzset{ + seagull/.pic={ + % Code for a "seagull". Do you see it?... + \draw (-3mm,0) to [bend left] (0,0) to [bend left] (3mm,0); + }, +}}] +\tikz \draw + (0,0) to [bend left] + pic [near start] {seagull} + pic {seagull} + pic [sloped, near end] {seagull} (4,0); +\end{codeexample} + + \medskip + \textbf{The options of a node.} + As always, any given \meta{options} apply only to the pic and have no + effect outside. As for nodes, most ``outside'' options also apply to the + pics, but not the ``action'' options like |draw| or |fill|. These must be + given in the \meta{options} of the pic. + + \medskip + \textbf{The code of a pic.} + As stated earlier, the main job of a pic is to execute some code in a scope + that is shifted according to the last point on the path or to the |at| + position specified in the pic. It was also claimed that this code is + specified by the \meta{pic type}. However, this specification is somewhat + indirect. What really happens is the following: When a |pic| is + encountered, the current path is suspended and a new internal scope is + started. The \meta{options} are executed and also the \meta{pic type} (as + explained in a moment). After all this is done, the code stored in the + following key gets executed: + + \begin{key}{/tikz/pics/code=\meta{code}} + This key stores the \meta{code} that should be drawn in the current + pic. Normally, setting this key is done by the \meta{pic type}, but you + can also set it in the \meta{options} and leave the \meta{pic type} + empty: + % +\begin{codeexample}[] +\tikz \pic [pics/code={\draw (-3mm,0) to[bend left] (0,0) + to[bend left] (3mm,0);}] + {}; % no pic type specified +\end{codeexample} + \end{key} + + Now, how does the \meta{pic type} set |pics/code|? It turns out that the + \meta{pic type} is actually just a list of keys that are executed with the + prefix |/tikz/pics/|. In the above examples, this ``list of keys'' just + consisted of the single key ``|seagull|'' that did not take any arguments, + but, in principle, you could provide any arbitrary text understood by + |\pgfkeys| here. This means that when we write |pic{seagull}|, \tikzname\ + will execute the key |/tikz/pics/seagull|. It turns out, see + Section~\ref{section-new-pic-types}, that this key is just a style set to + |code={\draw(-3mm,0)...;}|. Thus, |pic{seagull}| will cause the |pics/code| + key to be set to the text needed to draw the + seagull. + + Indeed, you can also use the \meta{pic type} simply to set the |code| of + the pic. This is useful for cases when you have some code that you ``just + want to execute, but do not want to define a new pic type''. Here is a + typical example where we use pics to add some markings to a path: + % +\begin{codeexample}[] +\tikz \draw (0,0) .. controls(1,0) and (2,1) .. (3,1) + foreach \t in {0, 0.125, ..., 1} { + pic [pos=\t] {code={\draw circle [radius=2pt];}} + }; +\end{codeexample} + + In our seagull example, we always explicitly used |\draw| to draw the + seagull. This implies that when a user writes something + |pic[fill]{seagull}| in the hope of having a ``filled'' seagull, nothing + special will happen: The |\draw| inside the pic explicitly states that the + path should be drawn, not filled, and the fact that in the surrounding + scope the |fill| option is set has no effect. The following key can be used + to change this: + % + \begin{key}{/tikz/pic actions} + This key is a style that can be used (only) inside the code of a pic. + There, it will set the ``action'' keys set inside the \meta{options} of + the pic (``actions'' are drawing, filling, shading, and clipping or any + combination thereof). + + To see how this key works, let us define the following pic: + % +\begin{codeexample}[code only] +\tikzset{ + my pic/.pic = { + \path [pic actions] (0,0) circle[radius=3mm]; + \draw (-3mm,-3mm) rectangle (3mm,3mm); + } +} +\end{codeexample} + % + In the code, whether or not the circle gets drawn/filled/shaded + depends on which options where given to the |pic| command when it + is used. In contrast, the rectangle will always (just) be drawn. + % +\tikzset{ + my pic/.pic = { + \path [pic actions] (0,0) circle[radius=3mm]; + \draw (-3mm,-3mm) rectangle (3mm,3mm); + } +} +\begin{codeexample}[ + width=6cm, + pre={\tikzset{ + my pic/.pic = { + \path [pic actions] (0,0) circle[radius=3mm]; + \draw (-3mm,-3mm) rectangle (3mm,3mm); + } +}}] +\tikz \pic {my pic}; \space +\tikz \pic [red] {my pic}; \space +\tikz \pic [draw] {my pic}; \space +\tikz \pic [draw=red] {my pic}; \space +\tikz \pic [draw, shading=ball] {my pic}; \space +\tikz \pic [fill=red!50] {my pic}; +\end{codeexample} + \end{key} + + \medskip + \textbf{Code executed behind or in front of the path.} + As for nodes, a pic can be ``behind'' the current path or ``in front of + it'' and, just as for nodes, the two options |behind path| and + |in front of path| are used to specify which is meant. In detail, if |node| + and |pic| are both used repeatedly on a path, in the resulting picture we + first see all nodes and pics with the |behind path| option set in the order + they appear on the path (nodes and pics are interchangeable in this + regard), then comes the path, and then come all nodes and pics that are in + front of the path in the order they appeared. + % +\begin{codeexample}[ + pre={\tikzset{ + seagull/.pic={ + % Code for a "seagull". Do you see it?... + \draw (-3mm,0) to [bend left] (0,0) to [bend left] (3mm,0); + }, +}}] +\tikz \fill [fill=blue!20] + (1,1) + -- (2,2) pic [behind path] {seagull} + -- (3,2) pic {seagull} + -- (3,1) pic [rotate=30] {seagull} + -- (2,1) pic [red, behind path] {seagull}; +\end{codeexample} + % + In contrast to nodes, a pic need not only be completely behind the path or + in front of the path as specified by the user. Instead, a pic type may also + specify that a certain part of the drawing should always be behind the path + and it may specify that a certain other part should always be before the + path. For this, the values of the following keys are relevant: + + \begin{key}{/tikz/pics/foreground code=\meta{code}} + This key stores \meta{code} that will always be drawn in front of the + current path, even when |behind path| is used. If |behind path| is not + used and |code| is (also) set, the code of |code| is drawn first, + following by the foreground \meta{code}. + \end{key} + + \begin{key}{/tikz/pics/background code=\meta{code}} + Like |foreground code|, only that the \meta{code} is always put behind + the path, except when the |behind path| option is applied to the pic, + then the background code is drawn in front of the ``behind path'' code. + \end{key} + + \medskip + \textbf{The foreach statement for pics.} + As for nodes, a pic specification may start with |foreach|. The effect and + semantics are the same as for nodes. + % +\begin{codeexample}[ + pre={\tikzset{ + seagull/.pic={ + % Code for a "seagull". Do you see it?... + \draw (-3mm,0) to [bend left] (0,0) to [bend left] (3mm,0); + }, +}}] +\tikz \pic foreach \x in {1,2,3} at (\x,0) {seagull}; +\end{codeexample} + + \medskip + \textbf{Styles for pics.} + The following styles influence how nodes are rendered: + % + \begin{stylekey}{/tikz/every pic (initially \normalfont empty)} + This style is installed at the beginning of every pic. + % +\begin{codeexample}[ + pre={\tikzset{ + seagull/.pic={ + % Code for a "seagull". Do you see it?... + \draw (-3mm,0) to [bend left] (0,0) to [bend left] (3mm,0); + }, +}}] +\begin{tikzpicture}[every pic/.style={scale=2,transform shape}] + \pic foreach \x in {1,2,3} at (\x,0) {seagull}; +\end{tikzpicture} +\end{codeexample} + \end{stylekey} + + \medskip + \textbf{Name scopes.} + You can specify a \meta{name} for a pic using the key |name=|\meta{name} or + by giving the name in parenthesis inside the pic's specification. The + effect of this is, for once, quite different from what happens for nodes: + All that happens is that |name prefix| is set to \meta{name} at the + beginning of the pic. + + The |name prefix| key was already introduced in the description of the + |node| command: It allows you to set some text that is prefixed to all + nodes in a scope. For pics this makes particular sense: All nodes defined + by a pic's code can be referenced from outside the pic with the prefix + provided. + + To see how this works, let us add some nodes to the code of the seagull: + % +\begin{codeexample}[code only] +\tikzset{ + seagull/.pic={ + % Code for a "seagull". Do you see it?... + \coordinate (-left wing) at (-3mm,0); + \coordinate (-head) at (0,0); + \coordinate (-right wing) at (3mm,0); + + \draw (-left wing) to [bend left] (0,0) (-head) to [bend left] (-right wing); + } +} +\end{codeexample} + % +\tikzset{ + seagull/.pic={ + % Code for a "seagull". Do you see it?... + \coordinate (-left wing) at (-3mm,0); + \coordinate (-head) at (0,0); + \coordinate (-right wing) at (3mm,0); + + \draw (-left wing) to [bend left] (0,0) (-head) to [bend left] (-right wing); + } +} + + Now, we can use it as follows: + % +\begin{codeexample}[code only] +\tikz { + \pic (Emma) {seagull}; + \pic (Alexandra) at (0,1) {seagull}; + + \draw (Emma-left wing) -- (Alexandra-right wing); +} +\end{codeexample} + + Sometimes, you may also wish your pic to access nodes outside the pic + (typically, because they are given as parameters). In this case, the name + prefix gets in the way since the nodes outside the picture do not have this + prefix. The trick is to locally reset the name prefix to the value it had + outside the picture, which is achieved using the following style: + + \begin{key}{/tikz/name prefix ..} + This key is available only inside the code of a pic. There, it + (locally) changes the name prefix to the value it had outside the pic. + This allows you to access nodes outside the current pic. + \end{key} + + \medskip + \textbf{Animations for pics.} + Just as for nodes, you can use the attribute--colon syntax to add an + animation to a pic: + % +\begin{codeexample}[ + preamble={\usetikzlibrary{animations}}, + animation list={0.5,1,1.5,2}, + pre={\tikzset{ + seagull/.pic={ + % Code for a "seagull". Do you see it?... + \coordinate (-left wing) at (-3mm,0); + \coordinate (-head) at (0,0); + \coordinate (-right wing) at (3mm,0); + % + \draw (-left wing) to [bend left] (0,0) (-head) to [bend left] (-right wing); + } +}}, +] +\tikz { + \pic :rotate={0s="0", 20s="90"} {seagull}; + \pic at (1.5,1.5) {seagull}; +} +\end{codeexample} + % + Naturally, you can also use animations in the code of a picture: + % +\begin{codeexample}[ + preamble={\usetikzlibrary{animations}}, + animation list={0.5,1,1.5,2}, + width=3cm, +] +\begin{tikzpicture} [flapping seagull/.pic={ + \draw (0,0) :path={ + 0s= {"{(180:3mm) to [bend left] (0,0) to [bend left] (0:3mm)}"=base}, + 1s= "{(160:3mm) to [bend left] (0,0) to [bend left] (20:3mm)}", + 2s= "{(180:3mm) to [bend left] (0,0) to [bend left] (0:3mm)}", + repeats }; + }] + \pic :rotate={0s="0", 20s="90"} {flapping seagull}; + \pic at (1.5,1.5) {flapping seagull}; +\end{tikzpicture} +\end{codeexample} + % +\end{pathoperation} + +There are two general purpose keys that pics may find useful: + +\begin{key}{/tikz/pic text=\meta{text}} + This macro stores the \meta{text} in the macro |\tikzpictext|, which is + |\let| to |\relax| by default. Setting the |pic text| to some value is the + ``preferred'' way of communicating a (single) piece of text that should + become part of a pic (typically of a node). In particular, the |quotes| + library maps quoted parameters to this key. +\end{key} + +\begin{key}{/tikz/pic text options=\meta{options}} + This macro stores the \meta{options} in the macro |\tikzpictextoptions|, + which is |\let| to the empty string by default. The |quotes| library maps + options for quoted parameters to this key. +\end{key} + + +\subsubsection{The Quotes Syntax} +\label{section-pic-quotes} + +When you load the |quotes| library, you can use the ``quotes syntax'' inside +the options of a pic. Recall that for nodes this syntax is used to add a label +to a node. For pics, the quotes syntax is used to set the |pic text| key. +Whether or not the pic type's code takes this key into consideration is, +however, up to the key. + +In detail, when the |quotes| library is loaded, each time a key--value pair in +a list of options passed to an |pic| starts with |"|, the key--value pair must +actually be a string of the following form: +% +\begin{quote} + |"|\meta{text}|"|\opt{|'|}\opt{\meta{options}} +\end{quote} +% +This string is transformed into the following: +% +\begin{quote} + |every pic quotes/.try,pic text=|\meta{text}|, pic text options={|\meta{options}|}| +\end{quote} + +As example of a pic type that takes these values into account is the |angle| +pic type: +% +\begin{codeexample}[preamble={\usetikzlibrary{angles,quotes}}] +\tikz \draw (3,0) coordinate (A) + -- (0,1) coordinate (B) + -- (1,2) coordinate (C) + pic [draw, "$\alpha$"] {angle}; +\end{codeexample} + +As described in Section~\ref{section-label-quotes}, the apostrophe becomes part +of the \meta{options}, when present. As can be seen above, the following style +is executed: +% +\begin{stylekey}{/tikz/every pic quotes (initially \normalfont empty)} +\end{stylekey} + + +\subsection{Defining New Pic Types} +\label{section-new-pic-types} + +As explained in the description of the |pic| command, in order to define a new +pic type you need to +% +\begin{enumerate} + \item define a key with the path prefix |/tikz/pics| that + \item sets the key |/tikz/pics/code| to the code of the pic. +\end{enumerate} + +It turns out that this is easy enough to achieve using styles: + +\begin{codeexample}[code only] +\tikzset{ + pics/seagull/.style ={ + % Ok, this is the key that should, when + % executed, set the code key: + code = { % + \draw (...) ... ; + } + } +} +\end{codeexample} + +Even though the above pattern is easy enough, there is a special so-called key +handler that allows us to write even simpler code, namely: +% +\begin{codeexample}[code only] +\tikzset{ + seagull/.pic = { + \draw (...) ... ; + } +} +\end{codeexample} + +\begin{handler}{{.pic}|=|\meta{some code}} + This handler can only be used with a key with the prefix |/tikz/|, so you + should normally use it only as an option to a \tikzname\ command or to the + |\tikzset| command. It takes the \meta{key}'s path and, inside that path, + it replaces |/tikz/| by |/tikz/pics/| (so, basically, it adds the + ``missing'' |pics| part of the path). Then, it sets up things so that the + resulting name to key is a style that executes |code=some code|. +\end{handler} + +In almost all cases, the |.pic| key handler will suffice to setup keys. +However, there are cases where you really need to use the first version using +|.style| and |code=|: +% +\begin{itemize} + \item Whenever your pic type needs to set the foreground or the background + code. + \item In case of complicated arguments given to the keys. +\end{itemize} + +As an example, let us define a simple pic that draws a filled circle behind the +path. Furthermore, we make the circle's radius a parameter of the pic: +% +\begin{codeexample}[] +\tikzset{ + pics/my circle/.style = { + background code = { \fill circle [radius=#1]; } + } +} +\tikz [fill=blue!30] + \draw (0,0) pic {my circle=2mm} -- (1,1) pic {my circle=5mm}; +\end{codeexample} |