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I would like to draw an arrow that begins as a highly blurry rectangle and ends in a defined (no blur) shape. Is this possible in TikZ? A less preferable alternative would be a sequence of aligned arrow shapes, each less blurred than the previous one. Here is what I have so far (I could not find any command in TikZ to add blur):

\documentclass[border=1cm]{standalone}

\usepackage{tikz}

\begin{document}
\begin{tikzpicture}
    \def \ty {0.5}
    \def \by {-0.5}
    \fill[gray] (-0, \by) rectangle (10, \ty);
    \fill[gray] (9, -1) -- (9, 1) -- (11, 0) -- cycle;

    \def \tyinc {0.8}
    \def \byinc {-0.8}
    \foreach \x\en in {0/1,2/3,4/5, 6/7} {
        % Bonus question: Why does the left side of Event 1 tick not align exactly with the edge of the rectangle?
        \draw[gray, ultra thick] (\x,\ty) -- (\x,\tyinc) node [black, above] {Event \en};}

    \foreach \x\en in {1/2,3/4,5/6, 7/8} {
        \draw[gray, ultra thick] (\x,\by) -- (\x,\byinc) node [black, below] {Event \en};
    }
\end{tikzpicture}
\end{document}

Which looks like: LaTeX output

Here is an example of the less preferable option 2 that I drew on Inkscape (I don't know how to do option 1, one arrow, with Inkscape either): option 2

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  • 2,432
jsb
  • 454
  • Image blurring isn't part of TikZ, see https://tex.stackexchange.com/questions/295100/partial-or-entire-image-blurring-in-tikz and the answers posted there. – Skillmon Nov 05 '19 at 14:30
  • 1
    However, you could get that effect with a \pgfdeclarefunctionalshading (but that's nothing I can...) – Skillmon Nov 05 '19 at 14:40
  • 1
    It would seem a better option to fade from transparent to completely opaque rather than using a blur. – Werner Nov 05 '19 at 21:52

1 Answers1

13

UPDATE: This is an attempt to address all your comments on the color gradient (path fading) and control of the length. The length and some other parameters have been made pgf keys, which you can adjust at the beginning. 

\documentclass[tikz,border=1cm]{standalone}
\usetikzlibrary{decorations.markings,fadings,shadings}
\tikzset{blurring/.cd,amplitude/.initial=2mm,drop factor/.initial=0.006,line
width/.initial=1cm,%<-width of the arrow line
length/.initial=9cm,%<- length of the arrow
tick prominence/.initial=0.8cm,%<- length of the ticks
color/.code={\colorlet{myarrowcolor}{#1}},
color=gray}%<- try e.g. color=blue ;-)
\begin{tikzfadingfrompicture}[name=fade right] 
\shade[left color=transparent!0,
right color=transparent!100] 
    (0,-\pgfkeysvalueof{/tikz/blurring/line width}) rectangle 
    (\pgfkeysvalueof{/tikz/blurring/length}+\pgfkeysvalueof{/tikz/blurring/line width},\pgfkeysvalueof{/tikz/blurring/line width}); 
\end{tikzfadingfrompicture}

\begin{document}
\begin{tikzpicture}[font=\sffamily]
  \newcommand{\bkv}[1]{\pgfkeysvalueof{/tikz/blurring/#1}}
  \begin{scope}[local bounding box=faded]
    % this is the main routine. it draws little rectangles along the upper 
    % and lower border of the path. The size of these rectangles decreases.
    % The decrease is exponential and depends on the drop factor, larger
    % values imply faster decrease (initially it is 0.006).
    \draw[myarrowcolor,line width=\bkv{line width},postaction={decorate,decoration={markings,
    mark=between positions 0 and 1 step 1pt with {
        \pgfmathsetmacro{\myamp}{exp(-(\pgfkeysvalueof{/pgf/decoration/mark info/sequence number}*\bkv{drop factor}))}
        \pgfmathsetmacro{\myoldamp}{exp(-((\pgfkeysvalueof{/pgf/decoration/mark info/sequence number}-1)*\bkv{drop factor}))}
        \shade[top color=white,bottom color=myarrowcolor] 
        (0pt,0.49*\bkv{line width}-\myoldamp*\bkv{amplitude}) 
        -- (0pt,0.49*\bkv{line width}+\myoldamp*\bkv{amplitude}) 
        -- (1.1pt,0.49*\bkv{line width}+\myamp*\bkv{amplitude}) 
        -- (1.1pt,0.49*\bkv{line width}-\myamp*\bkv{amplitude});
        \shade[top color=myarrowcolor,bottom color=white] 
        (0pt,-0.49*\bkv{line width}+\myoldamp*\bkv{amplitude}) 
        -- (0pt,-0.49*\bkv{line width}-\myoldamp*\bkv{amplitude}) 
        -- (1.1pt,-0.49*\bkv{line width}-\myamp*\bkv{amplitude}) 
        -- (1.1pt,-0.49*\bkv{line width}+\myamp*\bkv{amplitude});}}}] 
        (0,0) -- (\bkv{length}, 0);
    % the parts left of the arrow are patched together  
    % left      
    \shade[left color=white,right color=myarrowcolor] 
     (-3*\bkv{amplitude},-0.5*\bkv{line width}+\bkv{amplitude})
      rectangle (0,0.5*\bkv{line width}-\bkv{amplitude});
    % top left  
    \shade[upper left=white,upper right=white,lower left=white,lower right=myarrowcolor] 
     (-3*\bkv{amplitude},0.5*\bkv{line width}-\bkv{amplitude})
      rectangle (0,0.5*\bkv{line width}+\bkv{amplitude});
    % bottom left  
    \shade[upper left=white,upper right=myarrowcolor,lower left=white,lower right=white] 
    (-3*\bkv{amplitude},-0.5*\bkv{line width}+\bkv{amplitude})
    rectangle (0,-0.5*\bkv{line width}-\bkv{amplitude}); 
    %
    \fill[myarrowcolor] (\bkv{length}-\bkv{line width},-\bkv{line width}) 
    -- (\bkv{length}-\bkv{line width},\bkv{line width}) 
    -- (\bkv{length}+\bkv{line width}, 0) -- cycle;
    %
    \foreach \x/\en in {0/1,2/3,4/5, 6/7} {
        % Bonus question: Why does the left side of Event 1 tick not align exactly with the edge of the rectangle?
        % Answer: because lines have a thickness
        \draw[myarrowcolor, ultra thick] (\x*1cm+\pgflinewidth/2,0) 
        -- (\x*1cm+\pgflinewidth/2,\bkv{tick prominence}) node [black, above] {Event \en};}
    %
    \foreach \x/\en in {1/2,3/4,5/6, 7/8} {
        \draw[myarrowcolor, ultra thick] (\x*1cm+\pgflinewidth/2,0) -- 
        (\x*1cm+\pgflinewidth/2,-\bkv{tick prominence}) node [black, below] {Event \en};
    }
  \end{scope}
  \fill[white,path fading=fade right] (faded.south west) rectangle
      (faded.north east);
\end{tikzpicture}
\end{document}

enter image description here

This is a pic version thereof. Of course, I do not know what things should be adjustable. The pic illustrates a bit what the keys do. 

\documentclass[tikz,border=1cm]{standalone}
\usetikzlibrary{decorations.markings,fadings,shadings}
\tikzset{pics/blurred arrow/.style={code={
\tikzset{blurring/.cd,#1}
\begin{pgfinterruptpicture}%
\begin{tikzfadingfrompicture}[name=fade right] 
\shade[left color=transparent!0,
right color=transparent!100] 
    (0,-\pgfkeysvalueof{/tikz/blurring/line width}) rectangle 
    (\pgfkeysvalueof{/tikz/blurring/length}+\pgfkeysvalueof{/tikz/blurring/line width},\pgfkeysvalueof{/tikz/blurring/line width}); 
\end{tikzfadingfrompicture}%
\end{pgfinterruptpicture}
  \newcommand{\bkv}[1]{\pgfkeysvalueof{/tikz/blurring/##1}}
  \begin{scope}[local bounding box=faded]
    % this is the main routine. it draws little rectangles along the upper 
    % and lower border of the path. The size of these rectangles decreases.
    % The decrease is exponential and depends on the drop factor, larger
    % values imply faster decrease (initially it is 0.006).
    \draw[myarrowcolor,line width=\bkv{line width},postaction={decorate,decoration={markings,
    mark=between positions 0 and 1 step 1pt with {
        \pgfmathsetmacro{\myamp}{exp(-(\pgfkeysvalueof{/pgf/decoration/mark info/sequence number}*\bkv{drop factor}))}
        \pgfmathsetmacro{\myoldamp}{exp(-((\pgfkeysvalueof{/pgf/decoration/mark info/sequence number}-1)*\bkv{drop factor}))}
        \shade[top color=white,bottom color=myarrowcolor] 
        (0pt,0.49*\bkv{line width}-\myoldamp*\bkv{amplitude}) 
        -- (0pt,0.49*\bkv{line width}+\myoldamp*\bkv{amplitude}) 
        -- (1.1pt,0.49*\bkv{line width}+\myamp*\bkv{amplitude}) 
        -- (1.1pt,0.49*\bkv{line width}-\myamp*\bkv{amplitude});
        \shade[top color=myarrowcolor,bottom color=white] 
        (0pt,-0.49*\bkv{line width}+\myoldamp*\bkv{amplitude}) 
        -- (0pt,-0.49*\bkv{line width}-\myoldamp*\bkv{amplitude}) 
        -- (1.1pt,-0.49*\bkv{line width}-\myamp*\bkv{amplitude}) 
        -- (1.1pt,-0.49*\bkv{line width}+\myamp*\bkv{amplitude});}}}] 
        (0,0) -- (\bkv{length}, 0);
    % the parts left of the arrow are patched together  
    % left      
    \shade[left color=white,right color=myarrowcolor] 
     (-3*\bkv{amplitude},-0.5*\bkv{line width}+\bkv{amplitude})
      rectangle (0,0.5*\bkv{line width}-\bkv{amplitude});
    % top left  
    \shade[upper left=white,upper right=white,lower left=white,lower right=myarrowcolor] 
     (-3*\bkv{amplitude},0.5*\bkv{line width}-\bkv{amplitude})
      rectangle (0,0.5*\bkv{line width}+\bkv{amplitude});
    % bottom left  
    \shade[upper left=white,upper right=myarrowcolor,lower left=white,lower right=white] 
    (-3*\bkv{amplitude},-0.5*\bkv{line width}+\bkv{amplitude})
    rectangle (0,-0.5*\bkv{line width}-\bkv{amplitude}); 
    %
    \fill[myarrowcolor] (\bkv{length}-\bkv{line width},-\bkv{line width}) 
    -- (\bkv{length}-\bkv{line width},\bkv{line width}) 
    -- (\bkv{length}+\bkv{line width}, 0) -- cycle;
    %
    \pgfmathtruncatemacro{\imax}{-1+\bkv{length}/1cm}
    \foreach \XX in {1,...,\imax}
    {\ifodd\XX
    \draw[myarrowcolor, ultra thick] (\XX*1cm+\pgflinewidth/2-1cm,0) 
    -- (\XX*1cm+\pgflinewidth/2-1cm,\bkv{tick prominence}) 
    node [black, above] {Event \XX};
    \else
    \draw[myarrowcolor, ultra thick] (\XX*1cm+\pgflinewidth/2-1cm,0) 
    -- (\XX*1cm+\pgflinewidth/2-1cm,-\bkv{tick prominence}) 
    node [black, below] {Event \XX};
    \fi
    }
  \end{scope}
  \fill[white,path fading=fade right] (faded.south west) rectangle
      (faded.north east);   
}},blurring/.cd,amplitude/.initial=2mm,drop factor/.initial=0.006,line
width/.initial=1cm,%<-width of the arrow line
length/.initial=9cm,%<- length of the arrow
tick prominence/.initial=0.8cm,%<- length of the ticks
color/.code={\colorlet{myarrowcolor}{#1}},
color=gray}%
\begin{document}
\begin{tikzpicture}[font=\sffamily]
  \pic{blurred arrow={color=blue,amplitude=2.4mm,drop factor=0.005}};
\end{tikzpicture}
\end{document}

enter image description here

OLDER PARTS. It is fairly easy to blur out single objects with shadows.blur. 

\documentclass[tikz,border=3mm]{standalone}
\usetikzlibrary{shapes.arrows,shadows.blur}
\tikzset{marrow/.style={minimum height=1.6cm,minimum width=1.2cm,
        single arrow, single arrow
        head extend=.125cm, single arrow head indent=0cm}}
\begin{document}
    \begin{tikzpicture}
     \path foreach \X in {1,...,4} 
    {(2.5*\X-2.5,0) node[marrow,fill=gray,blur shadow={shadow blur steps=10,shadow xshift=0pt,shadow yshift=0pt,shadow scale=1.2-\X*0.05}]{}};
   \end{tikzpicture}    
\end{document}

enter image description here

Or some more fancy option.

\documentclass[tikz,border=3mm]{standalone}
\usetikzlibrary{shapes.arrows,shadows.blur}
\newcounter{ishadow}
\tikzset{marrow/.style={minimum height=1.6cm,minimum width=1.2cm,
        single arrow, draw=none,rounded corners=1pt,single arrow
        head extend=.125cm, single arrow head indent=0cm},
    multi shadow/.style={/utils/exec=\setcounter{ishadow}{0}%
   \loop\stepcounter{ishadow} \ifnum\value{ishadow}<#1
   \tikzset{blur shadow={shadow blur steps=10,shadow xshift=0.5ex-rnd*1ex,shadow yshift=0.5ex-rnd*1ex,opacity=0.0,fill opacity=0.25,}}
  \repeat}}
\begin{document}
    \begin{tikzpicture}
     \path foreach \X in {1,...,4} 
     {(2.5*\X-2.5,0) node[marrow,fill=gray,multi shadow=\the\numexpr20-5*\X]{} node[marrow,fill=gray]{} };
   \end{tikzpicture}    
\end{document}

enter image description here

  • Thanks! I will start playing with that, I think the one arrow might be improved by also adding a color gradient. For the single arrow case I don't feel it conveys the message (from abstraction to concreteness) well, since the outline of the arrow is preserved and clearly visible through the cases. – jsb Nov 05 '19 at 19:57
  • @jsb I added a version with path fading, which yields a gradient. –  Nov 05 '19 at 21:08
  • wow thanks! That looks quite good. I will play with it to try to make the ticks blend a bit better. – jsb Nov 05 '19 at 21:32
  • @jsb I would only extend them. –  Nov 05 '19 at 21:39
  • Perfect, extending the ticks is what I had in mind but was having some issues implementing it. How can I change the length of the arrow (currently it goes from 0 to 11)? I tried modifying the obvious parts but it did not work. – jsb Nov 05 '19 at 21:49
  • I tried modifying the number 11 (the original length) where it appeared, but I have figured out that the important value is on line 25 (currently set to 10). I have been studying the TikZ manual for a few weeks but honestly most of what is going on here escapes my current knowledge. – jsb Nov 05 '19 at 21:58
  • @jsb I added a more customizable version at the very beginning of my answer. –  Nov 06 '19 at 00:13
  • Awesome, I modified line 38 as (0,0) -- (0.9*\bkv{length}, 0); to prevent the rectangle from appearing passed the edges of the arrow head. – jsb Nov 06 '19 at 19:11