From 6f9e1680085e7bb4d258f6f8116369d122e196e1 Mon Sep 17 00:00:00 2001 From: Norbert Preining Date: Mon, 16 Jan 2023 03:03:27 +0000 Subject: CTAN sync 202301160303 --- .../base/doc/pgfmanual-en-tikz-transparency.tex | 895 +++++++++++++++++++++ 1 file changed, 895 insertions(+) create mode 100644 graphics/pgf/base/doc/pgfmanual-en-tikz-transparency.tex (limited to 'graphics/pgf/base/doc/pgfmanual-en-tikz-transparency.tex') diff --git a/graphics/pgf/base/doc/pgfmanual-en-tikz-transparency.tex b/graphics/pgf/base/doc/pgfmanual-en-tikz-transparency.tex new file mode 100644 index 0000000000..1e2a20aba7 --- /dev/null +++ b/graphics/pgf/base/doc/pgfmanual-en-tikz-transparency.tex @@ -0,0 +1,895 @@ +% 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{Transparency} +\label{section-tikz-transparency} + +\subsection{Overview} + +Normally, when you paint something using any of \tikzname's commands (this +includes stroking, filling, shading, patterns, and images), the newly painted +objects totally obscure whatever was painted earlier in the same area. + +You can change this behavior by using something that can be thought of as +``(semi)transparent colors''. Such colors do not completely obscure the +background, rather they blend the background with the new color. At first +sight, using such semitransparent colors might seem quite straightforward, but +the math going on in the background is quite involved and the correct handling +of transparency fills some 64 pages in the PDF specification. + +In the present section, we start with the different ways of specifying ``how +transparent'' newly drawn objects should be. The simplest way is to just +specify a percentage like ``60\% transparent''. A much more general way is to +use something that I call a \emph{fading}, also known as a soft mask or a mask. + +At the end of the section we address the problem of creating so-called +\emph{transparency groups}. This problem arises when you paint over a position +several times with a semitransparent color. Sometimes you want the effect to +accumulate, sometimes you do not. + +\emph{Note:} Transparency (or Opacity, as it may be called as well) is best +supported by the pdf\TeX\ driver. The \textsc{svg} driver also has some +support. The PostScript file format does not know about transparency. In +|dvips|-generated PostScript files, transparency of graphic objects is defined +through special commands that need further processing to become visible in the +\textsc{pdf} output. For this, a recent version of Ghostscript, preferably 9.52 +or newer, is required and its command line utility |ps2pdf| must be called with +option |-dALLOWPSTRANSPARENCY|. Older versions may need option |-dNOSAFER| +instead, but some advanced features, such as \emph{transparency groups} and +\emph{fadings}, may not work at all. Printers and other programs will typically +ignore opacity settings in PostScript files. + + +\subsection{Specifying a Uniform Opacity} + +Specifying a stroke and/or fill opacity is quite easy using the following +options. + +\begin{key}{/tikz/draw opacity=\meta{value}} + This option sets ``how transparent'' lines should be. A value of |1| means + ``fully opaque'' or ``not transparent at all'', a value of |0| means + ``fully transparent'' or ``invisible''. A value of |0.5| yields lines that + are semitransparent. + + Note that when you use PostScript as your output format, this option works + only with recent versions of Ghostscript. + % +\begin{codeexample}[] +\begin{tikzpicture}[line width=1ex] + \draw (0,0) -- (3,1); + \filldraw [fill=yellow!80!black,draw opacity=0.5] (1,0) rectangle (2,1); +\end{tikzpicture} +\end{codeexample} + % +\end{key} + +Note that the |draw opacity| options only sets the opacity of drawn lines. The +opacity of fillings is set using the option |fill opacity| (documented in +Section~\ref{section-fill-opacity}. The option |opacity| sets both at the same +time. + +\begin{key}{/tikz/opacity=\meta{value}} + Sets both the drawing and filling opacity to \meta{value}. + + The following predefined styles make it easier to use this option: + % + \begin{stylekey}{/tikz/transparent} + Makes everything totally transparent and, hence, invisible. + % +\begin{codeexample}[] +\tikz{\fill[red] (0,0) rectangle (1,0.5); + \fill[transparent,red] (0.5,0) rectangle (1.5,0.25); } +\end{codeexample} + \end{stylekey} + + \begin{stylekey}{/tikz/ultra nearly transparent} + Makes everything, well, ultra nearly transparent. + % +\begin{codeexample}[] +\tikz{\fill[red] (0,0) rectangle (1,0.5); + \fill[ultra nearly transparent] (0.5,0) rectangle (1.5,0.25); } +\end{codeexample} + \end{stylekey} + + \begin{stylekey}{/tikz/very nearly transparent} +\begin{codeexample}[] +\tikz{\fill[red] (0,0) rectangle (1,0.5); + \fill[very nearly transparent] (0.5,0) rectangle (1.5,0.25); } +\end{codeexample} + \end{stylekey} + + \begin{stylekey}{/tikz/nearly transparent} +\begin{codeexample}[] +\tikz{\fill[red] (0,0) rectangle (1,0.5); + \fill[nearly transparent] (0.5,0) rectangle (1.5,0.25); } +\end{codeexample} + \end{stylekey} + + \begin{stylekey}{/tikz/semitransparent} +\begin{codeexample}[] +\tikz{\fill[red] (0,0) rectangle (1,0.5); + \fill[semitransparent] (0.5,0) rectangle (1.5,0.25); } +\end{codeexample} + \end{stylekey} + + \begin{stylekey}{/tikz/nearly opaque} +\begin{codeexample}[] +\tikz{\fill[red] (0,0) rectangle (1,0.5); + \fill[nearly opaque] (0.5,0) rectangle (1.5,0.25); } +\end{codeexample} + \end{stylekey} + + \begin{stylekey}{/tikz/very nearly opaque} +\begin{codeexample}[] +\tikz{\fill[red] (0,0) rectangle (1,0.5); + \fill[very nearly opaque] (0.5,0) rectangle (1.5,0.25); } +\end{codeexample} + \end{stylekey} + + \begin{stylekey}{/tikz/ultra nearly opaque} +\begin{codeexample}[] +\tikz{\fill[red] (0,0) rectangle (1,0.5); + \fill[ultra nearly opaque] (0.5,0) rectangle (1.5,0.25); } +\end{codeexample} + \end{stylekey} + + \begin{stylekey}{/tikz/opaque} + This yields completely opaque drawings, which is the default. + % +\begin{codeexample}[] +\tikz{\fill[red] (0,0) rectangle (1,0.5); + \fill[opaque] (0.5,0) rectangle (1.5,0.25); } +\end{codeexample} + \end{stylekey} +\end{key} + +\begin{key}{/tikz/fill opacity=\meta{value}} + This option sets the opacity of fillings. In addition to filling + operations, this opacity also applies to text and images. + + Note, again, that when you use PostScript as your output format, this + option works only with recent versions of Ghostscript. + % +\begin{codeexample}[] +\begin{tikzpicture}[thick,fill opacity=0.5] + \filldraw[fill=red] (0:1cm) circle (12mm); + \filldraw[fill=green] (120:1cm) circle (12mm); + \filldraw[fill=blue] (-120:1cm) circle (12mm); +\end{tikzpicture} +\end{codeexample} + +\begin{codeexample}[] +\begin{tikzpicture} + \fill[red] (0,0) rectangle (3,2); + + \node at (0,0) {\huge A}; + \node[fill opacity=0.5] at (3,2) {\huge B}; +\end{tikzpicture} +\end{codeexample} + % +\end{key} + +\begin{key}{/tikz/text opacity=\meta{value}} + Sets the opacity of text labels, overriding the |fill opacity| setting. + % +\begin{codeexample}[] +\begin{tikzpicture}[every node/.style={fill,draw}] + \draw[line width=2mm,blue!50,line cap=round] (0,0) grid (3,2); + + \node[opacity=0.5] at (1.5,2) {Upper node}; + \node[draw opacity=0.8,fill opacity=0.2,text opacity=1] + at (1.5,0) {Lower node}; +\end{tikzpicture} +\end{codeexample} + % +\end{key} + +Note the following effect: If you set up a certain opacity for stroking or +filling and you stroke or fill the same area twice, the effect accumulates: +% +\begin{codeexample}[] +\begin{tikzpicture}[fill opacity=0.5] + \fill[red] (0,0) circle (1); + \fill[red] (1,0) circle (1); +\end{tikzpicture} +\end{codeexample} + +Often, this is exactly what you intend, but not always. You can use +transparency groups, see the end of this section, to change this. + + +\subsection{Blend Modes} +\label{section-blend-modes} + +A \emph{blend mode} specifies how colors mix when you paint on a canvas. +Normally, if you paint a red box on a green circle, the red color will +completely replace the green circle. However, in some situations you might also +wish the red color to somehow ``mix'' or ``blend'' with the green circle. We +already saw that, using transparency, we can draw something without completely +obscuring the background. \emph{Blending} is a similar operation, only here we +mix colors in more complicated ways. + +\emph{Note:} Blending is a rather ``advanced'' feature of \textsc{pdf}. Most +renderers, let alone printers, will have trouble rendering blending correctly. + +\begin{key}{/tikz/blend mode=\meta{mode}} + Sets the current blend mode to \meta{mode}. Here \meta{mode} must be one of + the modes listed below. More details on these modes can also be found in + Section~7.2.4 of the \textsc{pdf} Specification, version~1.7. + + In the following example, the blend mode is only used and set inside a + transparency group (see also Section~\ref{section-transparency-groups}). + This is because most renderers (viewing programs) have trouble rendering + blending correctly otherwise. For instance, at the time of writing, the + versions of Adobe's Reader and Apple's Preview render the following drawing + very differently, if the transparency group is not used in the following + example. + % +\begin{codeexample}[] +\tikz { + \begin{scope}[transparency group] + \begin{scope}[blend mode=screen] + \fill[red!90!black] ( 90:.6) circle (1); + \fill[green!80!black] (210:.6) circle (1); + \fill[blue!90!black] (330:.6) circle (1); + \end{scope} + \end{scope} +} +\end{codeexample} + + Because of the trouble with rendering blending correctly outside + transparency groups, there is a special key that establishes a transparency + group and sets a blend mode simultaneously: + + \begin{key}{/tikz/blend group=\meta{mode}} + This key can only be used with a scope (like |transparency group|). It + will cause the current scope to become a transparency group and, inside + this group, the blend mode will be set to \meta{mode}. + % +\begin{codeexample}[] +\tikz [blend group=screen] { + \fill[red!90!black] ( 90:.6) circle (1); + \fill[green!80!black] (210:.6) circle (1); + \fill[blue!90!black] (330:.6) circle (1); +} +\end{codeexample} + \end{key} + + Here is an overview of the effects of the different available blend modes. + In the examples, we always have three circles drawn on top of each other + (as in the example code earlier): We start with a triple of pure red, + green, and blue. Below it, we have a triple of light versions of these + three colors (|red!50|, |green!50|, and |blue!50|). Next comes the triple + yellow, cyan, and magenta; again with a triple of light versions below it. + The large example consists of three balls (produced using |ball color|) + having the colors red, green, and blue, are drawn on top of each other just + like the circles. + + \definecolor{rg}{rgb}{1,1,0} + \definecolor{gb}{rgb}{0,1,1} + \definecolor{br}{rgb}{1,0,1} + + \def\makeline#1#2#3{\leavevmode + \hbox to 40mm{#1\hss}\ \hbox to + 20.5mm{#2\hss}\ \begin{minipage}[t]{88.5mm}\raggedright#3\end{minipage}\par + \textcolor{black!25}{\hrule height1pt} + } + + \def\showmode#1#2{ + \makeline{ + \tikz [blend mode=#1,baseline=-.5ex] { + \fill[red] ( 90:.5em) circle (.75em); + \fill[green] (210:.5em) circle (.75em); + \fill[blue] (330:.5em) circle (.75em); + \scoped[yshift=-2.5em]{ + \fill[red!50] ( 90:.5em) circle (.75em); + \fill[green!50] (210:.5em) circle (.75em); + \fill[blue!50] (330:.5em) circle (.75em); + } + } + \tikz [blend mode=#1,baseline=-.5ex] { + \fill[rg] ( 90:.5em) circle (.75em); + \fill[gb] (210:.5em) circle (.75em); + \fill[br] (330:.5em) circle (.75em); + \scoped[yshift=-2.5em]{ + \fill[rg!50] ( 90:.5em) circle (.75em); + \fill[gb!50] (210:.5em) circle (.75em); + \fill[br!50] (330:.5em) circle (.75em); + } + } + \tikz [blend mode=#1,baseline=-.5ex+1.25em] { + \shade[ball color=red] ( 90:1em) circle (1.5em); + \shade[ball color=green] (210:1em) circle (1.5em); + \shade[ball color=blue] (330:1em) circle (1.5em); + }}{\verb|#1|}{#2}% + % this argument was changed from {|#1|} + % --> see + } + + \medskip + \makeline{\emph{Example}}{\emph{Mode}}{\emph{Explanations quoted from + Table~7.2 of the \textsc{pdf} Specification, Version~1.7}} + \showmode{normal}{When painting a pixel with a some color (called the + ``source color''), the background color (called the ``backdrop'') is + completely ignored.} + \showmode{multiply}{Multiplies the backdrop and source color values. The + result color is always at least as dark as either of the two + constituent colors. Multiplying any color with black produces black; + multiplying with white leaves the original color unchanged. Painting + successive overlapping objects with a color other than black or white + produces progressively darker colors.} + \showmode{screen}{Multiplies the complements of the backdrop and source + color values, then complements the result. The result color is always + at least as light as either of the two constituent colors. Screening + any color with white produces white; screening with black leaves the + original color unchanged. The effect is similar to projecting multiple + photographic slides simultaneously onto a single screen.} + \showmode{overlay}{Multiplies or screens the colors, depending on the + backdrop color value. Source colors overlay the backdrop while + preserving its highlights and shadows. The backdrop color is not + replaced but is mixed with the source color to reflect the lightness or + darkness of the backdrop.} + \showmode{darken}{Selects the darker of the backdrop and source colors. The + backdrop is replaced with the source where the source is darker; + otherwise, it is left unchanged.} + \showmode{lighten}{Selects the lighter of the backdrop and source colors. + The backdrop is replaced with the source where the source is lighter; + otherwise, it is left unchanged.} + \showmode{color dodge}{Brightens the backdrop color to reflect the source + color. Painting with black produces no changes.} + \showmode{color burn}{Darkens the backdrop color to reflect the source + color. Painting with white produces no change.} + \showmode{hard light}{Multiplies or screens the colors, depending on the + source color value. The effect is similar to shining a harsh spotlight + on the backdrop.} + \showmode{soft light}{Darkens or lightens the colors, depending on the + source color value. The effect is similar to shining a diffused + spotlight on the backdrop.} + \showmode{difference}{Subtracts the darker of the two constituent colors + from the lighter color. Painting with white inverts the backdrop color; + painting with black produces no change.} + \showmode{exclusion}{Produces an effect similar to that of the Difference + mode but lower in contrast. Painting with white inverts the backdrop + color; painting with black produces no change.} + \showmode{hue}{Creates a color with the hue of the source color and the + saturation and luminosity of the backdrop color.} + \showmode{saturation}{Creates a color with the saturation of the source + color and the hue and luminosity of the backdrop color. Painting with + this mode in an area of the backdrop that is a pure gray (no + saturation) produces no change.} + \showmode{color}{Creates a color with the hue and saturation of the source + color and the luminosity of the backdrop color. This preserves the gray + levels of the backdrop and is useful for coloring monochrome images or + tinting color images.} + \showmode{luminosity}{Creates a color with the luminosity of the source + color and the hue and saturation of the backdrop color. This produces + an inverse effect to that of the Color mode.} +\end{key} + + +\subsection{Fadings} + +For complicated graphics, uniform transparency settings are not always +sufficient. Suppose, for instance, that while you paint a picture, you want the +transparency to vary smoothly from completely opaque to completely transparent. +This is a ``shading-like'' transparency. For such a form of transparency I will +use the term \emph{fading} (as a noun). They are also known as \emph{soft +masks}, \emph{opacity masks}, \emph{masks}, or \emph{soft clips}. + + +\subsubsection{Creating Fadings} + +How do we specify a fading? This is a bit of an art since the underlying +mechanism is quite powerful, but a bit difficult to use. + +Let us start with a bit of terminology. A \emph{fading} specifies for each +point of an area the transparency of that point. This transparency can by any +number between 0 and 1. A \emph{fading picture} is a normal graphic that, in a +way to be described in a moment, determines the transparency of points inside +the fading. Each fading has an underlying fading picture. + +The fading picture is a normal graphic drawn using any of the normal graphic +drawing commands. A fading and its fading picture are related as follows: Given +any point of the fading, the transparency of this point is determined by the +luminosity of the fading picture at the same position. The luminosity of a +point determines ``how bright'' the point is. The brighter the point in the +fading picture, the more opaque is the point in the fading. In particular, a +white point of the fading picture is completely opaque in the fading and a +black point of the fading picture is completely transparent in the fading. (The +background of the fading picture is always transparent in the fading as if the +background were black.) + +It is rather counter-intuitive that a \emph{white} pixel of the fading picture +will be \emph{opaque} in the fading and a \emph{black} pixel will be +\emph{transparent}. For this reason, \tikzname\ defines a color called +|transparent| that is the same as |black|. The nice thing about this definition +is that the color |transparent!|\meta{percentage} in the fading picture yields +a pixel that is \meta{percentage} percent transparent in the fading. + +Turning a fading picture into a normal picture is achieved using the following +commands, which are \emph{only defined in the library}, namely the library +|fadings|. So, to use them, you have to say |\usetikzlibrary{fadings}| first. + +\begin{environment}{{tikzfadingfrompicture}\oarg{options}} + This command works like a |{tikzpicture}|, only the picture is not shown, + but instead a fading is defined based on this picture. To set the name of + the picture, use the |name| option (which is normally used to set the name + of a node). + % + \begin{key}{/tikz/name=\marg{name}} + Use this option with the |{tikzfadingfrompicture}| environment to set + the name of the fading. You \emph{must} provide this option. + \end{key} + + The following shading is 2cm by 2cm and gets more and more transparent from + left to right, but is 50\% transparent for a large circle in the middle. + % +{\ifpgfmanualexternalize\tikzexternaldisable\fi +\begin{codeexample}[preamble={\usetikzlibrary{fadings,patterns}}] +\begin{tikzfadingfrompicture}[name=fade right with circle] + \shade[left color=transparent!0, + right color=transparent!100] (0,0) rectangle (2,2); + \fill[transparent!50] (1,1) circle (0.7); +\end{tikzfadingfrompicture} + +% Now we use the fading in another picture: +\begin{tikzpicture} + % Background + \fill [black!20] (-1.2,-1.2) rectangle (1.2,1.2); + \pattern [pattern=checkerboard,pattern color=black!30] + (-1.2,-1.2) rectangle (1.2,1.2); + + \fill [path fading=fade right with circle,red] (-1,-1) rectangle (1,1); +\end{tikzpicture} +\end{codeexample} + % + In the next example we create a fading picture that contains some text. + When the fading is used, we only see the shading ``through it''. + % +\begin{codeexample}[preamble={\usetikzlibrary{fadings,patterns}}] +\begin{tikzfadingfrompicture}[name=tikz] + \node [text=transparent!20] + {\fontencoding{T1}\fontfamily{ptm}\fontsize{45}{45}\bfseries\selectfont + Ti\emph{k}Z}; +\end{tikzfadingfrompicture} + +% Now we use the fading in another picture: +\begin{tikzpicture} + \fill [black!20] (-2,-1) rectangle (2,1); + \pattern [pattern=checkerboard,pattern color=black!30] + (-2,-1) rectangle (2,1); + + \shade[path fading=tikz,fit fading=false, + left color=blue,right color=black] + (-2,-1) rectangle (2,1); +\end{tikzpicture} +\end{codeexample} +}% + + The same effect can also be achieved using knockout groups, see + Section~\ref{section-transparency-groups}. +\end{environment} + +\begin{plainenvironment}{{tikzfadingfrompicture}\oarg{options}} + The plain\TeX\ version of the environment. +\end{plainenvironment} + +\begin{contextenvironment}{{tikzfadingfrompicture}\oarg{options}} + The Con\TeX t version of the environment. +\end{contextenvironment} + +\begin{command}{\tikzfading\oarg{options}} + This command is used to define a fading similarly to the way a shading is + defined. In the \meta{options} you should + % + \begin{enumerate} + \item use the |name=|\meta{name} option to set a name for the fading, + \item use the |shading| option to set the name of the shading that you + wish to use, + \item extra options for setting the colors of the shading (typically + you will set them to the color |transparent!|\meta{percentage}). + \end{enumerate} + % + Then, a new fading named \meta{name} will be created based on the shading. + % +\begin{codeexample}[preamble={\usetikzlibrary{fadings,patterns}}] +\tikzfading[name=fade right, + left color=transparent!0, + right color=transparent!100] + +% Now we use the fading in another picture: +\begin{tikzpicture} + % Background + \fill [black!20] (-1.2,-1.2) rectangle (1.2,1.2); + \path [pattern=checkerboard,pattern color=black!30] + (-1.2,-1.2) rectangle (1.2,1.2); + + \fill [red,path fading=fade right] (-1,-1) rectangle (1,1); +\end{tikzpicture} +\end{codeexample} + +\begin{codeexample}[preamble={\usetikzlibrary{fadings,patterns}}] +\tikzfading[name=fade out, + inner color=transparent!0, + outer color=transparent!100] + +% Now we use the fading in another picture: +\begin{tikzpicture} + % Background + \fill [black!20] (-1.2,-1.2) rectangle (1.2,1.2); + \path [pattern=checkerboard,pattern color=black!30] + (-1.2,-1.2) rectangle (1.2,1.2); + + \fill [blue,path fading=fade out] (-1,-1) rectangle (1,1); +\end{tikzpicture} +\end{codeexample} + % +\end{command} + + +\subsubsection{Fading a Path} + +A fading specifies for each pixel of a certain area how transparent this pixel +will be. The following options are used to install such a fading for the +current scope or path. + +\pgfdeclarefading{fade down}{% + \tikzset{top color=pgftransparent!0,bottom color=pgftransparent!100} + \pgfuseshading{axis} +} +\pgfdeclarefading{fade inside}{% + \tikzset{inner color=pgftransparent!90,outer color=pgftransparent!30} + \pgfuseshading{radial} +} + +\begin{key}{/tikz/path fading=\meta{name} (default \normalfont scope's setting)} + This option tells \tikzname\ that the current path should be faded with the + fading \meta{name}. If no \meta{name} is given, the \meta{name} set for the + whole scope is used. Similarly to options like |draw| or |fill|, this + option is reset for each path, so you have to add it to each path that + should be faded. You can also specify |none| as \meta{name}, in which case + fading for the path will be switched off in case it has been switched on by + previous options or styles. + % +\begin{codeexample}[preamble={\usetikzlibrary{fadings,patterns}}] +\begin{tikzpicture}[path fading=south] + % Checker board + \fill [black!20] (0,0) rectangle (4,3); + \pattern [pattern=checkerboard,pattern color=black!30] + (0,0) rectangle (4,3); + + \fill [color=blue] (0.5,1.5) rectangle +(1,1); + \fill [color=blue,path fading=north] (2.5,1.5) rectangle +(1,1); + + \fill [color=red,path fading] (1,0.75) ellipse (.75 and .5); + \fill [color=red] (3,0.75) ellipse (.75 and .5); +\end{tikzpicture} +\end{codeexample} + + \begin{key}{/tikz/fit fading=\meta{boolean} (default true, initially true)} + When set to |true|, the fading is shifted and resized (in exactly the + same way as a shading) so that it covers the current path. When set to + |false|, the fading is only shifted so that it is centered on the + path's center, but it is not resized. This can be useful for + special-purpose fadings, for instance when you use a fading to ``punch + out'' something. + \end{key} + + \begin{key}{/tikz/fading transform=\meta{transformation options}} + The \meta{transformation options} are applied to the fading before it + is used. For instance, if \meta{transformation options} is set to + |rotate=90|, the fading is rotated by 90 degrees. + % +\begin{codeexample}[ + preamble={\usetikzlibrary{fadings,patterns}}, + pre={\pgfdeclarefading{fade down}{% + \tikzset{top color=pgftransparent!0,bottom color=pgftransparent!100} + \pgfuseshading{axis} +}}] +\begin{tikzpicture}[path fading=fade down] + % Checker board + \fill [black!20] (0,0) rectangle (4,1.5); + \path [pattern=checkerboard,pattern color=black!30] (0,0) rectangle (4,1.5); + + \fill [red,path fading,fading transform={rotate=90}] + (1,0.75) ellipse (.75 and .5); + \fill [red,path fading,fading transform={rotate=30}] + (3,0.75) ellipse (.75 and .5); +\end{tikzpicture} +\end{codeexample} + \end{key} + + \begin{key}{/tikz/fading angle=\meta{degree}} + A shortcut for |fading transform={rotate=|\meta{degree}|}|. + \end{key} + + Note that you can ``fade just about anything''. In particular, you can fade + a shading. + % +\begin{codeexample}[preamble={\usetikzlibrary{fadings,patterns}}] +\begin{tikzpicture} + % Checker board + \fill [black!20] (0,0) rectangle (4,4); + \path [pattern=checkerboard,pattern color=black!30] (0,0) rectangle (4,4); + + \shade [ball color=blue,path fading=south] (2,2) circle (1.8); +\end{tikzpicture} +\end{codeexample} + + The |fade inside| of the following example is more transparent in the + middle than on the outside. + % +\begin{codeexample}[preamble={\usetikzlibrary{fadings,patterns}}] +\tikzfading[name=fade inside, + inner color=transparent!80, + outer color=transparent!30] +\begin{tikzpicture} + % Checker board + \fill [black!20] (0,0) rectangle (4,4); + \path [pattern=checkerboard,pattern color=black!30] (0,0) rectangle (4,4); + + \shade [ball color=red] (3,3) circle (0.8); + \shade [ball color=white,path fading=fade inside] (2,2) circle (1.8); +\end{tikzpicture} +\end{codeexample} + + Note that adding the |path fading| option to a node fades the (background) + path, not the text itself. To fade the text, you need to use a scope fading + (see below). +\end{key} + +Note that using fadings in conjunction with patterns can create visually rather +pleasing effects: +% +\begin{codeexample}[preamble={\usetikzlibrary{fadings,patterns,shadows}}] +\tikzfading[name=middle, + top color=transparent!50, + bottom color=transparent!50, + middle color=transparent!20] +\begin{tikzpicture} + \node [circle,circular drop shadow, + pattern=horizontal lines dark blue, + path fading=south, + minimum size=3.6cm] {}; + \pattern [path fading=north, + pattern=horizontal lines dark gray] + (0,0) circle (1.8cm); + \pattern [path fading=middle, + pattern=crosshatch dots light steel blue] + (0,0) circle (1.8cm); +\end{tikzpicture} +\end{codeexample} + + +\subsubsection{Fading a Scope} + +In addition to fading individual paths, you may also wish to ``fade a scope'', +that is, you may wish to install a fading that is used globally to specify the +transparency for all objects drawn inside a scope. This effect can also be +thought of as a ``soft clip'' and it works in a similar way: You add the +|scope fading| option to a path in a scope -- typically the first one -- and +then all subsequent drawings in the scope are faded. You will use a +|transparency group| in conjunction, see the end of this section. + +\begin{key}{/tikz/scope fading=\meta{fading}} + In principle, this key works in exactly the same way as the |path fading| + key. The only difference is, that the effect of the fading will persist + after the current path till the end of the scope. Thus, the \meta{fading} + is applied to all subsequent drawings in the current scope, not just to the + current path. In this regard, the option works very much like the |clip| + option. (Note, however, that, unlike the |clip| option, fadings to not + accumulate unless a transparency group is used.) + + The keys |fit fading| and |fading transform| have the same effect as for + |path fading|. Also that, just as for |path fading|, providing the + |scope fading| option with a |{scope}| only sets the name of the fading to + be used. You have to explicitly provide the |scope fading| with a path to + actually install a fading. + % +\begin{codeexample}[preamble={\usetikzlibrary{fadings,patterns}}] +\begin{tikzpicture} + \fill [black!20] (-2,-2) rectangle (2,2); + \pattern [pattern=checkerboard,pattern color=black!30] + (-2,-2) rectangle (2,2); + + % The bounding box of the shading: + \draw [red] (-50bp,-50bp) rectangle (50bp,50bp); + + \path [scope fading=south,fit fading=false] (0,0); + % fading is centered at its natural size + + \fill[red] ( 90:1) circle (1); + \fill[green] (210:1) circle (1); + \fill[blue] (330:1) circle (1); +\end{tikzpicture} +\end{codeexample} + + In the following example we resize the fading to the size of the whole + picture: + % +\begin{codeexample}[preamble={\usetikzlibrary{fadings,patterns}}] +\begin{tikzpicture} + \fill [black!20] (-2,-2) rectangle (2,2); + \pattern [pattern=checkerboard,pattern color=black!30] + (-2,-2) rectangle (2,2); + + \path [scope fading=south] (-2,-2) rectangle (2,2); + + \fill[red] ( 90:1) circle (1); + \fill[green] (210:1) circle (1); + \fill[blue] (330:1) circle (1); +\end{tikzpicture} +\end{codeexample} + + Scope fadings are also needed if you wish to fade a node. + % +\begin{codeexample}[preamble={\usetikzlibrary{fadings}}] +\tikz \node [scope fading=south,fading angle=45,text width=3.5cm] +{ + This is some text that will fade out as we go right + and down. It is pretty hard to achieve this effect in + other ways. +}; +\end{codeexample} + % +\end{key} + + +\subsection{Transparency Groups} +\label{section-transparency-groups} + +Consider the following cross and sign. They ``look wrong'' because we can see +how they were constructed, while this is not really part of the desired effect. +% +\begin{codeexample}[] +\begin{tikzpicture}[opacity=.5] + \draw [line width=5mm] (0,0) -- (2,2); + \draw [line width=5mm] (2,0) -- (0,2); +\end{tikzpicture} +\end{codeexample} + +\begin{codeexample}[preamble={\usetikzlibrary{shapes.symbols}}] +\begin{tikzpicture} + \node at (0,0) [forbidden sign,line width=2ex,draw=red,fill=white] {Smoking}; + + \node [opacity=.5] + at (2,0) [forbidden sign,line width=2ex,draw=red,fill=white] {Smoking}; +\end{tikzpicture} +\end{codeexample} + +Transparency groups are used to render them correctly: +% +\begin{codeexample}[] +\begin{tikzpicture}[opacity=.5] + \begin{scope}[transparency group] + \draw [line width=5mm] (0,0) -- (2,2); + \draw [line width=5mm] (2,0) -- (0,2); + \end{scope} +\end{tikzpicture} +\end{codeexample} + +\begin{codeexample}[preamble={\usetikzlibrary{shapes.symbols}}] +\begin{tikzpicture} + \node at (0,0) [forbidden sign,line width=2ex,draw=red,fill=white] {Smoking}; + + \begin{scope}[opacity=.5,transparency group] + \node at (2,0) [forbidden sign,line width=2ex,draw=red,fill=white] + {Smoking}; + \end{scope} +\end{tikzpicture} +\end{codeexample} + +\begin{key}{/tikz/transparency group=\oarg{options}} + This option can be given to a |scope|. It will have the following effect: + The scope's contents is stroked\,/\penalty0\,filled ``ignoring any outside + transparency''. This means, all previous transparency settings are ignored + (you can still set transparency inside the group, but never mind). For + instance, in the forbidden sign example, the whole sign is first painted + (conceptually) like the image on the left hand side. Note that some pixels + of the sign are painted multiple times (up to three times), but only the + last color ``wins''. + + Then, when the scope is finished, it is painted as a whole. The \emph{fill} + transparency settings are now applied to the resulting picture. For + instance, the pixel that has been painted three times is just red at the + end, so this red color will be blended with whatever is ``behind'' the + group on the page. + % +\begin{codeexample}[preamble={\usetikzlibrary{patterns,shapes.symbols}}] +\begin{tikzpicture} + \pattern[pattern=checkerboard,pattern color=black!15](-1,-1) rectangle (3,1); + \node at (0,0) [forbidden sign,line width=2ex,draw=red,fill=white] {Smoking}; + + \begin{scope}[transparency group,opacity=.5] + \node at (2,0) [forbidden sign,line width=2ex,draw=red,fill=white] + {Smoking}; + \end{scope} +\end{tikzpicture} +\end{codeexample} + + Note that in the example, the |opacity=.5| is not active inside the + transparency group: The group is only established at beginning of the scope + and all options given to the |{scope}| environment are set before the group + is established. To change the opacity \emph{inside} the group, you need to + open another scope inside it or use the |opacity| key with a command inside + the group: + % +\begin{codeexample}[preamble={\usetikzlibrary{patterns,shapes.symbols}}] +\begin{tikzpicture} + \pattern[pattern=checkerboard,pattern color=black!15](-1,-1) rectangle (3,1); + \node at (0,0) [forbidden sign,line width=2ex,draw=red,fill=white] {Smoking}; + + \begin{scope}[transparency group,opacity=.5] + \node (s) at (2,0) [forbidden sign,line width=2ex,draw=red,fill=white] + {Smoking}; + + \draw [opacity=.5, line width=2ex, blue] (1.2,0) -- (2.8,0); + \end{scope} +\end{tikzpicture} +\end{codeexample} + + The \meta{options} are a list of comma-separated options: + % + \begin{itemize} + \item \declare{|knockout|} When this option is given inside the + \meta{options}, the group becomes a so-called \emph{knockout} + group. This means, essentially, that inside the group everything is + painted as if the ``opacity'' of a line or area were just another + color channel. In particular, if you paint a pixel with opacity $0$ + inside a knockout group, this pixel becomes perfectly transparent + immediately. In contrast, painting a pixel with something of + opacity $0$ normally has no effect. + + Not all renderers, let alone printers, will support this. At the + time of writing, Apple's Preview will not show the following + correctly (you should see the text \tikzname\ in the middle): + % +\begin{codeexample}[] +\begin{tikzpicture} + \shade [left color=red,right color=blue] (-2,-1) rectangle (2,1); + \begin{scope}[transparency group=knockout] + \fill [white] (-1.9,-.9) rectangle (1.9,.9); + \node [opacity=0,font=\fontencoding{T1}\fontfamily{ptm}\fontsize{45}{45}\bfseries] + {Ti\emph{k}Z}; + \end{scope} +\end{tikzpicture} +\end{codeexample} + % + In the example, we first draw a large shading and then, inside the + transparency group ``overwrite'' most of this shading by a big + white rectangle. The interesting part is the text of the node, + which has opacity |0|. Normally, this would mean that nothing is + shown. However, in a knockout group, we ``paint'' the text with an + ``opacity zero'' color. The effect is that part of the totally + opaque white rectangle gets overwritten by a perfectly transparent + area (namely exactly the area taken up by the pixels of the text). + When this whole knockout group is then placed on top of the + shading, the shading will ``shine through'' at the knocked-out + pixels. + + \item \declare{|isolated|}|=false| A group can be isolated or not. By + default, they are isolated, since this is typically what you want. + For details on what isolated groups are, exactly, see Section~7.3.4 + of the \textsc{pdf} Specification, version~1.7. + \end{itemize} + + Note that when a transparency group is created, \tikzname\ must correctly + determine the size of the material inside the group. Usually, this is no + problem, but when you use things like |overlay| or |transform canvas|, + trouble may result. In this case, please consult + Section~\ref{section-transparency} on how to sidestep this problem in such + cases. +\end{key} + + +%%% Local Variables: +%%% mode: latex +%%% TeX-master: "pgfmanual" +%%% End: -- cgit v1.2.3