Solution 1
A combination of grid and clip.
If you want to change the line width of the grid change it in the scope (so that the shifting uses the correct \pgflinewidth).
line cap=rect makes a nice grid at the corners.
The shifting makes sure that the clip doesn't cut anything from the grid’s line width.
Code
\documentclass{article}
%\usepackage{tikz}
\tikzset{Shift/.style 2 args={shift={(+#1\pgflinewidth,+#2\pgflinewidth)}}}
\begin{document}
\begin{tikzpicture}
\begin{scope}
\clip ([Shift=--] 1,0) -- + ([Shift=22] \numOfRows,\numOfRows) -| +(-1,0) -- cycle;
\draw[line cap=rect] (0,0) grid ++ (\numOfRows,\numOfRows);
\end{scope}
\begin{scope}
\clip ([Shift=--] 2,0) -- + ([Shift=22] \numOfRows,\numOfRows) -| +([Shift=20] \numOfRows+1,0) -- cycle;
\draw[line cap=rect] (3,0) grid ++ (\numOfRows,\numOfRows);
\end{scope}
\draw (0,-1.5) -- + (\numOfRows+3,\numOfRows+3);
\foreach \Dot in {0,1,2}{
\fill (\numOfRows/2,\numOfRows+1+\Dot/2) circle [radius=.125cm];
\fill (\numOfRows+4+\Dot/2,\numOfRows/2) circle [radius=.125cm];
}
\end{tikzpicture}
\end{document}
Solution 2
Good ol’ lines. The right part is obtained by rotating the left part around the middle point of that diagonal line. (There are other ways.)
Code
\documentclass{article}
\usepackage{tikz}
\newcommand*{\numOfRows}{8}
\begin{document}
\begin{tikzpicture}
\foreach \Rotate in {0,180}{
\begin{scope}[rotate around={\Rotate:(\numOfRows/2+1.5,\numOfRows/2)}]
\foreach \Row in {1,...,\numOfRows}{
\draw[line cap=rect] (0,\Row-1) -- ++ (\Row,0) -- ++ (0,\numOfRows+1-\Row);
}
\draw (\numOfRows,\numOfRows) -| (0,0);
\end{scope}
}
\draw (0,-1.5) -- + (\numOfRows+3,\numOfRows+3);
\foreach \Dot in {0,1,2}{
\fill (\numOfRows/2,\numOfRows+1+\Dot/2) circle [radius=.125cm];
\fill (\numOfRows+4+\Dot/2,\numOfRows/2) circle [radius=.125cm];
}
\end{tikzpicture}
\end{document}
Output

thick.) – Sean Allred Apr 13 '13 at 09:08(10,9). – Ronny Apr 13 '13 at 09:23