How filling angle symbol?

Question

In the thread Insertion of perpendicular symbol at intersection of two perpendicular lines, Jake proposed a very useful command to mark a right angle. I tried to color the symbol, but I get only half colored.

  \documentclass{standalone}
  \usepackage{pgfplots}
  \usetikzlibrary{calc}
  \pgfplotsset{compat=1.13}
    \tikzset{
     right angle quadrant/.code={
     \pgfmathsetmacro\quadranta{{1,1,-1,-1}[#1-1]}   
     \pgfmathsetmacro\quadrantb{{1,-1,-1,1}[#1-1]}},
      right angle quadrant=1, 
      right angle length/.code={\def\rightanglelength{#1}},   
      right angle length=2ex,
      right angle symbol/.style n args={3}{
      insert path={
        let \p0 = ($(#1)!(#3)!(#2)$) in    
            let \p1 = ($(\p0)!\quadranta*\rightanglelength!(#3)$), 
            \p2 = ($(\p0)!\quadrantb*\rightanglelength!(#2)$) in 
            let \p3 = ($(\p1)+(\p2)-(\p0)$) in 
        (\p1) -- (\p3) -- (\p2)
     }
     }
     }

  \begin{document}

  \begin{tikzpicture}[extended line/.style={shorten >=-#1,shorten <=-#1}]

  \begin{axis}[
    restrict x to domain=-4:5, xmax=5, xmin=-4,
    restrict y to domain=-2:4, ymax=4, ymin=-2,
    x=0.7cm,
    y=0.7cm,
    axis x line=middle,
    axis y line=middle,
    major tick style=black,
    axis line style = thick,
    tickwidth=0.1cm,
    grid=both,
    xtick={-3,...,4},
    ytick={-1,...,3},
    yticklabels={,,},
    xticklabels={,,},
    extra x ticks={-4,5}, 
    extra x tick label={\null}, 
    extra y ticks={-2,4}, 
    extra y tick label={\null},
    extra tick style={tick style={draw=none}},
    xlabel=$x$,ylabel=$y$,
    every axis x label/.style={
    at={(ticklabel* cs:1.01)},
   anchor=west,
   },
   every axis y label/.style={
   at={(ticklabel* cs:1.01)},
   anchor=south,
   },
  samples=1000,
  >=stealth,
  ]


 \coordinate [label=above right : $A$] (A) at (-2,3);
 \coordinate [label=below left : $B$](B) at (-3,1);
 \coordinate [label=above right : $C$](C) at (4,0);
 \coordinate [label=below right : $H$] (H) at ($(B)!(A)!(C)$);

 \draw [thick] (A)--(B)--(C)--cycle;
 \draw [thick,extended line=3cm] (A)--(H);
 \draw [fill=red,right angle quadrant=1,right angle symbol={B}{C}{A}];

 \node[below=2pt] at (1,0) {$1$};
 \node[left=2pt] at (0,1) {$1$};
 \node[below left=2pt] at (0,0) {$0$};

 \node[thick] at (A) {+};
 \node[thick] at (B) {+};
 \node[thick] at (C) {+};

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

Answer 1

Replacing (\p1) -- (\p3) -- (\p2) with (\p1) -- (\p3) -- (\p2) --(\p0) will fill in the symbol. The original macro at Insertion of perpendicular symbol at intersection of two perpendicular lines was designed to draw the perpendiular symbol assuming that the other lines were already in place; Thus, it was not doing a complete cycle.

Notes:

• In the version below I am using the macro from a follow-up question to the one where you got the code: Right Angle Symbol Alignment with TikZ/Calc. But, for this specfic case either version of the right angle quadrant= seems to work fine:
• Also, I recommend filling the symbol in before drawing the other lines as I have done below.

Code:

\documentclass{standalone}
\usepackage{pgfplots}
\usetikzlibrary{calc}
\pgfplotsset{compat=1.13}

%% https://tex.stackexchange.com/questions/114680/right-angle-symbol-alignment-with-tikz-calc
\tikzset{
    right angle quadrant/.code={
        \pgfmathsetmacro\quadranta{{1,1,-1,-1}[#1-1]}     % Arrays for selecting quadrant
        \pgfmathsetmacro\quadrantb{{1,-1,-1,1}[#1-1]}},
    right angle quadrant=1, % Make sure it is set, even if not called explicitly
    right angle length/.code={\def\rightanglelength{#1}},   % Length of symbol
    right angle length=2ex, % Make sure it is set...
    right angle symbol/.style n args={3}{
        insert path={
            let \p0 = ($(#1)!(#3)!(#2)$),     % Intersection
                \p1 = ($(\p0)!\quadranta*\rightanglelength!(#3)$), % Point on base line
                \p2 = ($(\p0)!\quadrantb*\rightanglelength!(#2)$), % Point on perpendicular line
                \p3 = ($(\p1)+(\p2)-(\p0)$) in  % Corner point of symbol
            (\p1) -- (\p3) -- (\p2) --(\p0)%% <-- Added '--(\p0)'
        }
    }
}

\begin{document}

\begin{tikzpicture}[extended line/.style={shorten >=-#1,shorten <=-#1}]

\begin{axis}[
    restrict x to domain=-4:5, xmax=5, xmin=-4,
    restrict y to domain=-2:4, ymax=4, ymin=-2,
    x=0.7cm,
    y=0.7cm,
    axis x line=middle,
    axis y line=middle,
    major tick style=black,
    axis line style = thick,
    tickwidth=0.1cm,
    grid=both,
    xtick={-3,...,4},
    ytick={-1,...,3},
    yticklabels={,,},
    xticklabels={,,},
    extra x ticks={-4,5}, 
    extra x tick label={\null}, 
    extra y ticks={-2,4}, 
    extra y tick label={\null},
    extra tick style={tick style={draw=none}},
    xlabel=$x$,ylabel=$y$,
    every axis x label/.style={
    at={(ticklabel* cs:1.01)},anchor=west},
    every axis y label/.style={
    at={(ticklabel* cs:1.01)}, anchor=south},
    samples=1000,
    >=stealth,
]


 \coordinate [label=above right : $A$] (A) at (-2,3);
 \coordinate [label=below left : $B$](B) at (-3,1);
 \coordinate [label=above right : $C$](C) at (4,0);
 \coordinate [label=below right : $H$] (H) at ($(B)!(A)!(C)$);

 \draw [fill=red, right angle quadrant=1,right angle symbol={B}{C}{A}];
 \draw [thick] (A)--(B)--(C)--cycle;
 \draw [thick,extended line=3cm] (A)--(H);

 \node[below=2pt] at (1,0) {$1$};
 \node[left=2pt] at (0,1) {$1$};
 \node[below left=2pt] at (0,0) {$0$};

 \node[thick] at (A) {+};
 \node[thick] at (B) {+};
 \node[thick] at (C) {+};

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