easier grid connections

gistfile1.txt

\documentclass[tikz]{standalone}
\usepackage{tikz}
\tikzset{
pics/grid/.style n args={9}{
code = {%       
    \pgfmathsetmacro \nxx{#6 - 1}
    \pgfmathsetmacro \nyy{#7 - 1}       

    %CENTRAL DOT
    \filldraw[black] circle (2pt) coordinate (-c); 

    % SOURCES
    \foreach \i in {1,...,#6}{
        \foreach \j in {1,...,#7}{
            \pgfmathsetmacro \x {(\i - (#6 + 1)/2)*#8*#2 + (\j - (#7 + 1)/2)*#9*#3} 
            \pgfmathsetmacro \y {(\i - (#6 + 1)/2)*#8*#4 + (\j - (#7 + 1)/2)*#9*#5}

            \node[circle,minimum size=5mm,fill=#1, draw=black, line width = 0.2mm] (-\i-\j) at (\x,\y) {};
        }
    }

    % draw horizontal connections
    \foreach [evaluate={\ii=int(\i+1)}] \i in {1,...,\nxx}
      \foreach \j in {1,...,#7}
          \draw [#1, dashed, line width = 0.2mm] (-\i-\j) -- (-\ii-\j);

    % draw vertical connections
    \foreach [evaluate={\jj=int(\j+1)}] \j in {1,...,\nyy}
      \foreach \i in {1,...,#6}
          \draw [#1, dashed, line width = 0.2mm] (-\i-\j) -- (-\i-\jj);


}}}

\begin{document}

%% PROPERTIES OF THE GRID
\def \nx{4}
\def \ny{3}
\def \dx{3}
\def \dy{2.2}

%% IDENTITY. UNDEFORMED ARRAY
\def \ai{1}     
\def \bi{0}
\def \ci{0}  
\def \di{1}

%% STRETCHING DEFORMATION MATRIX 
\def \af{0.8} 
\def \bf{0}
\def \cf{0}  
\def \df{1.2}

\begin{tikzpicture}
\pic (a) {grid={blue!15!white}{\ai}{\bi}{\ci}{\di}{\nx}{\ny}{\dx}{\dy}};
\pic (b) {grid={orange!75!red}{\af}{\bf}{\cf}{\df}{\nx}{\ny}{\dx}{\dy}};
\end{tikzpicture}

\end{document}