how to see the layout boxes in a math formula?

Question

Let's try a standard calculus formula, here the code

\documentclass[12pt]{article}
\begin{document}
$$ \int_0^\infty \frac{dx}{1+x^2} = \frac{\pi}{2} $$
\end{document}

Here is the result of the integral of rational function. Notice there is a polynomial and a fraction.

Is there a way to see an "annotated" version of this formula with the boxes. Here is what I found on a Microsoft page using their program opentype.

What are all the rectangles for? Is there any way to get a similar picture in LaTeX?

Answer 1

Wiht LuaTeX it is as easy as adding \usepackage{lua-visual-debug} to the preamble.

\documentclass[12pt]{article}
\usepackage{lua-visual-debug}
\begin{document}
\[ \int_0^\infty \frac{dx}{1+x^2} = \frac{\pi}{2} \]
\end{document}