3D 图 - 阶跃函数

Question

我想为步进函数生成 3D 图片，如下所示：

但我被卡住了。下面，我尝试了一些方法。

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{3d}

\begin{document}
\begin{tikzpicture}[scale=0.5]
  % Draw the axes
  \draw[->] (0,0,0) -- (8,0,0) node[below] {$y$};
  \draw[->] (0,0,0) -- (0,8,0) node[left] {$z$};
  \draw[->] (0,0,0) -- (0,0,5) node[above] {$x$};

  
  \pgfmathsetmacro{\numlevels}{4}
  \pgfmathsetmacro{\levelheight}{4}

 
  \foreach \x in {0,1,2,3,4,5,6,7} {
    \foreach \y in {0,...,\numlevels} {
      \draw (\x,\y,0) -- (\x,\y,\levelheight) -- (\x+1,\y,\levelheight) -- (\x+1,\y,0) -- cycle;
      \draw (\x,\y,0) -- (\x,\y,\levelheight) -- (\x,\y+1,\levelheight) -- (\x,\y+1,0) -- cycle;
      \draw (\x,\y+1,0) -- (\x,\y+1,\levelheight) -- (\x+1,\y+1,\levelheight) -- (\x+1,\y+1,0) -- cycle;
      \draw (\x+1,\y,0) -- (\x+1,\y,\levelheight) -- (\x+1,\y+1,\levelheight) -- (\x+1,\y+1,0) -- cycle;
    }
  }


  \node[align=center] at (-0.5,-1.1,2) {\resizebox{!}{0.5\height}{\footnotesize{$b=x_{2}$}}};
  \node[align=center] at (1.2,1,3) {\resizebox{!}{0.5\height}{\footnotesize{$b=x_{1}$}}};
\end{tikzpicture}
\end{document}

输出为：

任何解决方案或想法都会非常有帮助！