I want to animate rows of equations to look like they are manually written by hands on a piece of paper.

Requirements

• The equations must be decorated with minimal numbers of cluttering animating decorators.


• For each frame, the first part of an equation sticks to the left and the subsequent parts of the equations flow to the right. (Rather than the first part starts from the center and it get pushed to the left when the subsequent parts come).



• we can also animate fraction, integral, limit, etc. For example, frac{a}{b} will be animated to produce a followed by a horizontal line and followed by b. Another example, int_a^b will be animated as an integral sign followed by b that is followed by a.




• To make it more portable, not using beamer is preferred.

Question

How to achieve such requirements? I will give a bounty of 2000 for those who can provide me with a satisfying code. Any additional features from your creativity is also welcome!

MWE

Warning: the following code will spin undefinetely.

documentclass[12pt]{beamer}

usepackage{amsmath}

usepackage[active,tightpage]{preview}

PreviewBorder=12ptrelax

PreviewEnvironment{align*}



newcounter{counter}

newcommand{foo}[1]{stepcounter{counter}only<thecounter->{#1}}

begin{document}

begin{frame}

    begin{align*}

    foo{a}foo{+b}&foo{=1}\

    foo{frac{1}{2}}foo{+frac{3}{2}}foo{&=2}% I don't know whether "&" should be outside or inside "foo".

    end{align*}

end{frame}

end{document}

This is not a full answer but a longer reply to your comment. There are many things I do not understand about your approach, and here is a suggestion how to fix them. The main point is that IMHO your foo attempts to reinvent the wheel something beamer already has.

documentclass[12pt,beamer,preview,multi={gather*}]{standalone}

usepackage{amsmath,mathtools}

newcommand{foo}[1]{visible<+->{#1}}

newcommand{foop}[1]{only<+>{#1}}

newcommand{foopp}[1]{only<+->{#1}}

newcommand{fooint}[2]{foop{mathrlap{intlimits_{phantom{#1}}^{phantom{#2}}}}%

foop{mathrlap{intlimits_{#1}^{phantom{#2}}}}%

foo{intlimits_{#1}^{#2}}}

newcommand{foofrac}[2]{foop{mathrlap{genfrac{}{}{0pt}{0}{#1}{phantom{#2}}}}%

foop{mathrlap{frac{#1}{phantom{#2}}}}%

foo{frac{#1}{#2}}}



begin{document}

begin{standaloneframe}%showgenfrac

    begin{gather*}

    foo{a}foo{+}foo{b}foo{=}foo{1}\

    fooint{a}{b}foo{f}foo{(}foo{x}foo{)}

    foo{,mathsf{d}}foo{x}foo{=}foo{2}\

    foofrac{a}{b}

    foo{=}

    foofrac{c}{d}\[1cm]

    end{gather*}

end{standaloneframe}

end{document}

EDIT: Added a missing mathrlap, thanks to The Inventor of God (or reinventer of the wheel? ;-)!

As I said, this is an extended comment, not a full answer. I guess a full answer will have to allow one to nest these macros. With the tools above, one could write something like frac{a,b}{c} in such a way that first a appears, then b and finally the full thing. But it will be cumbersome. I could imagine to cook up a more automatized version with loops, but this will most likely be fragile. So I stop here.