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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{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 <https://sourceforge.net/p/pgf/bugs/486/>
- }
-
- \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: