pgfplots: problem with "non-smooth" intersection of two lines' ends

Question

I have a problem like the one in this question concerning a tikz drawing but for a pgfplots plot. I want to create a plot that has one region filled without opacity and a neighboring one filled with opacity. The transparent region should be coated by a solid line. I managed to get pretty much what I want with this code:

\documentclass{standalone}

\usepackage{pgfplots}
\pgfplotsset{compat=1.3}

\usepackage{pgfplotstable} % For \pgfplotstableread
\usepgfplotslibrary{external}
\tikzexternalize

\usepackage{filecontents}

\begin{filecontents}{total.dos}
0  0  0  0  0   
1  2 -2  2 -2  
2  4 -4  4 -4  
3  2 -2  2 -2  
4  0  0  0  0 
5  1 -1  0  0 
6  2 -2  0  0 
7  1 -1  0  0 
8  0  0  0  0 
THIS WAS: TOTAL
\end{filecontents}

\pgfplotstableread[comment chars={T}]{total.dos}\total

\begin{document}

% Set a filename for the next tikzpicture.
\tikzsetnextfilename{total_dos} 

\begin{tikzpicture}
\begin{axis}[ymax=7, ymin=-7, xlabel={Energy [eV]}, ylabel={Intensity}, legend pos=north east]

\addplot [restrict x to domain=4:8, no markers, draw=red, fill=red, fill opacity=0.3] table [x=0, y expr=\thisrowno{2} - \thisrowno{4}] {\total}; \addlegendentry{$2-4$}

\addplot [restrict x to domain=4:8, no markers, draw=blue, fill=blue, fill opacity=0.3] table [x=0, y expr=\thisrowno{1} - \thisrowno{3}] {\total}; \addlegendentry{$1-3$}

\addplot [restrict x to domain=0:4, no markers, draw=blue , fill=blue] table [x=0, y=3] {\total}; \addlegendentry{$3$}

\addplot [restrict x to domain=0:4, no markers, draw=red, fill=red] table [x=0, y=4] {\total}; \addlegendentry{$4$}

\end{axis}
\end{tikzpicture}
\end{document}

This gives the following picture:

The problem is the intersections of the coating lines' ends (those that come from the draw=<color> options). They are not smooth, but look like this:

My question: How can I get these things smooth?

Side note: I know that using the option draw=none gives the behaviour I want, but then I have no line surrounding the transparent region.

Edit:

I have stumbled upon something interesting: Adobe Acrobat X and SumatraPDF seem to handle the plots slightly differently. Acrobat cuts off the parts of the rightmost line endings that loom beyond the plotting domain (I don't know a better word for it) while SumatraPDF doesn't. Interestingly, this doesn't happen for the line endings on the left or in the middle (see picture above, which was made with Acrobat).

I'm not sure why this is so and whether it affects the possible solutions to my problems. Maybe this is an issue worth adressing in a different question? Or is this a mere PDF viewer question which shouldn't be asked here?

Answer 1

Since draw = none gives the correct behavoir, we can simplify the problem. Use draw = none around the red and blue regions in the domain = 0:4. Now if we do line join = round, line width = .08pt, we can still see a border around dulled regions but we only have one connection of the lines to worry about. However, since we used line width = .08pt, it is very hard to notice anything when zoomed in at 1600%.

As you can see, we still have a border:

and zoomed at 1600% we see no issues with the connection:

Would this be an acceptable solution for you?

---

Option 2:

\documentclass[tikz]{standalone}
\usetikzlibrary{arrows}
\begin{document}

\begin{tikzpicture}[]
  \begin{scope}
    \clip (0, 0) rectangle (8, 5);
    \filldraw[blue] (0, 0) -- (2, 4) -- (4, 0) -- cycle;
    \filldraw[blue, opacity = .3, draw = blue]
    (4, 0) -- (6, 2) -- (8, 0) -- cycle;
  \end{scope}

    \begin{scope}
    \clip (0, 0) rectangle (8, -5);
    \filldraw[red] (0, 0) -- (2, -4) -- (4, 0) -- cycle;
    \filldraw[red, opacity = .3, draw = red]
    (4, 0) -- (6, -2) -- (8, 0) -- cycle;
  \end{scope}
\end{tikzpicture}
\end{document}

Now all you need to do is draw the axis.

Then here is the intersection:

---

With darker outlines:

\documentclass[tikz]{standalone}
\usetikzlibrary{arrows}
\begin{document}

\begin{tikzpicture}[]
  \begin{scope}
    \clip (0, 0) rectangle (8, 5);
    \filldraw[blue] (0, 0) -- (2, 4) -- (4, 0) -- cycle;
    \filldraw[blue, opacity = .3, draw = blue]
    (4, 0) -- (6, 2) -- (8, 0) -- cycle;
    \draw[blue] (4, 0) -- (6, 2) -- (8, 0);
  \end{scope}

    \begin{scope}
    \clip (0, 0) rectangle (8, -5);
    \filldraw[red] (0, 0) -- (2, -4) -- (4, 0) -- cycle;
    \filldraw[red, opacity = .3, draw = red]
    (4, 0) -- (6, -2) -- (8, 0) -- cycle;
    \draw[red] (4, 0) -- (6, -2) -- (8, 0);
  \end{scope}
\end{tikzpicture}
\end{document}