Off the top of my head this might be worth investigating for simulating your code @...box, @...Fill and @...Clear commands.
(listed as backward compatible command in FoxPro Help)

basic syntax is:
@ < nTopRow >, < nLeftCol > to < nBottomRow >, < nRightColumn > [double | system]
and
@ < nTopRow >, < nLeftCol > fill to < nBottomRow >, < nRightColumn > [color scheme < nScheme > | color < nForeColor, nBackColor | cForeColor, cBackColor >

for example
@ 15.2, 30 say "this is a test" && notice decimal is permitted
@ 10, 1 fill to 20, 80 color gr+/gr
@ 10, 1 to 20, 80 double

These commands are from the (yech) DOS days but are very fast, and you can get creative (at least we thought we were back then < s >)

Don't know if they fit into your objective, but if all your trying to do is 'explode' a window put @..box into loop then display form in final size...

Hope this helps!

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>Does anyone knows how to copy a rectangle from an active form into memory and recover it later.

I'm trying to animate an splash form using the form width and height properties and the resize method but the result it's not very impressive but slower and fuzzy.

Here my Activate code:
for i = 1 to 10
this.height = i*10
this.width = i*10
endfor

Resize method
this.refresh.