Very nice. A couple of comments. Default height is too large for my monitor (1152x864) so I guess you must run 1280x1024+....

I did not like the grid. Having had a quick RTFS I changed withgrid => 1 to zero. This has multiple effects, but in short it does not remove the grid and it does destroy the geometry. If you just add a return in the draw_grid() function if withdgrid => 0 then you can lose the grid but see the undesirable side effects on the geometry (rotating the blocks is interesting). The easiest way to remove the grid (and retain the geometry) is simply to make it the same as the board colour.

    my $gridcolor      = $NO_GRID ? '#000000' : '#FFFFFF';
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The grid still gets drawn but is invisible, and all the withgrid code is redundant and can be removed. That saves fixing it ;-) I like the grid through the blocks anyway as it looks as I remember tetris looking.