Given the function
f(x)={3x6x<03x12x0\displaystyle {f{{\left({x}\right)}}}={\left\lbrace\begin{array}{cc} {3}{x}-{6}&{x}<{0}\\{3}{x}-{12}&{x}\geq{0}\end{array}\right.}

Calculate the following values:
f(1)=\displaystyle {f{{\left(-{1}\right)}}}=  
f(0)=\displaystyle {f{{\left({0}\right)}}}=  
f(2)=\displaystyle {f{{\left({2}\right)}}}=