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+% Copyright 2006 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 behaviour 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 adress 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 is best supported by the pdf\TeX\
+driver. The \textsc{svg} driver also has some support. For PostScript
+output, opacity is rendered correctly only with the most recent
+versions of GhostScript. Printers and other programs will typically
+ignore the opacity setting.
+
+
+
+\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=examplefill,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 setup 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{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 to transparency of the 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 lumonisity 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 where 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{percantage} per cent 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 changes gets more and more
+ transparent from left to right, but is 50\% transparent for a large
+ circle in the middle.
+\begin{codeexample}[]
+\begin{tikzfadingfrompicture}[name=fade right]
+ \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,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}[]
+\begin{tikzfadingfrompicture}[name=tikz]
+ \node [text=transparent!20]
+ {\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}
+\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 that 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}[]
+\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}[]
+\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}
+
+Aa 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}[]
+\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 is 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 ``punsh 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}[]
+\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}[]
+\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 more transparent in the middle than on the
+ outside.
+
+\begin{codeexample}[]
+\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}[]
+\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 addtion 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 excatly 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}[]
+\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}[]
+\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}[]
+\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}
+
+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}[]
+\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}[]
+\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}
+ This option can be given to a |scope|. It will have the following
+ effect: The scope's contents is stroked/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
+ picutre. 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.
+
+ Note that, depending on the driver, it is possible to directly put
+ objects in a transparency group that lie outside the picture. This
+ has to do with internal bounding box computations.
+ Section~\ref{section-transparency} explains how to sidestep this
+ problem.
+\end{key}
+
+
+
+%%% Local Variables:
+%%% mode: latex
+%%% TeX-master: "pgfmanual"
+%%% End: