Add uncertainty to time graph

graphics/time_table.tex

@@ -1,13 +1,15 @@
 \documentclass{standalone}
 \usepackage{tikz,pgfplots}
 \usepackage{siltex}
-\usetikzlibrary{arrows.meta,positioning}
+\usetikzlibrary{arrows.meta,positioning,calc,fadings}
 \pgfplotsset{compat=1.17}
 \begin{document}
 \begin{tikzpicture}
+    \pgfmathsetlengthmacro{\xbarvalue}{-3mm}
+    \pgfmathsetlengthmacro{\barwidthvalue}{4mm}
 \begin{axis}[
-    xbar=-3mm,
-    bar width=4mm,
+    xbar=\xbarvalue,
+    bar width=\barwidthvalue,
     xmin=0,
     xmax=21,
     width=85mm,
@@ -21,7 +23,18 @@
 ]
     \addplot[draw=red,fill=red!40] coordinates {(2,Problem Description) (3,Specifications) (3.5,Initial Design) (13,Feature Definition) (0.5,Test Protocol) (3,Development Cycle 1) (17,Development Cycle 2) (20,Software Development)};
     \addplot[draw=blue,fill=blue!40] coordinates {(2,Problem Description) (3,Specifications) (5,Initial Design) (6,Feature Definition) (1,Test Protocol) (3,Development Cycle 1) (13,Development Cycle 2)};
-\legend{Time Spend,Time Planned};
+    \legend{Time Spend,Time Planned};
+    \pgfmathsetlengthmacro{\baroffset}{\barwidthvalue+\xbarvalue/2}
+    \pgfmathsetlengthmacro{\smeer}{7mm}
+    \node (a) at ($(axis cs:3,Development Cycle 1)-(0.1mm,0mm)+(0mm,\baroffset)$) {};
+    \node (b) at ($(axis cs:3,Development Cycle 1)-(0.1mm,0mm)-(0mm,\baroffset)$) {};
+    \fill[white] (a) rectangle ++(\smeer,-\barwidthvalue-1mm);
+    \fill[red!40,path fading=east] (b) rectangle ++(\smeer,1mm);
+    \fill[blue!40,path fading=east] (a) rectangle ++(\smeer,-\barwidthvalue);
+    \draw[white] ($(a)$) -- +(\smeer,0mm) ++(0mm,-\barwidthvalue) -- +(\smeer,0mm);
+    \draw[white] ($(b)$) -- +(\smeer,0mm); 
+    \draw[blue,path fading=east] ($(a)$) -- +(\smeer,0mm) ++(0mm,-\barwidthvalue) -- +(\smeer,0mm);
+    \draw[red,path fading=east] ($(b)$) -- +(\smeer,0mm); 
 \end{axis}
 \end{tikzpicture}
 \end{document}