How to draw triangular grid in TikZ?

Question

Is there an easy way to draw a triangular grid in TikZ, like this?

Answer 1

Like Leo said: use \foreach and some math:

\usetikzlibrary{calc}

\newcommand*\rows{10}
\begin{tikzpicture}
    \foreach \row in {0, 1, ...,\rows} {
        \draw ($\row*(0.5, {0.5*sqrt(3)})$) -- ($(\rows,0)+\row*(-0.5, {0.5*sqrt(3)})$);
        \draw ($\row*(1, 0)$) -- ($(\rows/2,{\rows/2*sqrt(3)})+\row*(0.5,{-0.5*sqrt(3)})$);
        \draw ($\row*(1, 0)$) -- ($(0,0)+\row*(0.5,{0.5*sqrt(3)})$);
    }
\end{tikzpicture}

Answer 2

A funny solution (have you ever used lindenmayersystems library?):

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{lindenmayersystems}
\begin{document}
\begin{tikzpicture}
  \pgfdeclarelindenmayersystem{triangular grid}{\rule{F->F-F+++F--F}}
  \path[draw=black,
  l-system={triangular grid,step=1cm,
    angle=-60,axiom=F--F--F,order=4,
  }]
  lindenmayer system -- cycle;
\end{tikzpicture}
\end{document}

Answer 3

A slightly different solution using a matrix transformation and clipping:

\newcommand*{\rows}{10}
\pgfmathsetmacro{\xcoord}{cos(60)}
\pgfmathsetmacro{\ycoord}{sin(60)}

\begin{tikzpicture}
    \pgftransformcm{1}{0}{\xcoord}{\ycoord}{\pgfpointorigin} 

    \path[clip,preaction = {draw=black}] (\rows,0) -- (0,0) -- (0,\rows) -- cycle;
    \draw (0,0) grid (\rows,\rows);
    \foreach \x in {1,2,...,\rows} {
        \draw (0,\x) -- (\x,0);
    } 
\end{tikzpicture}