How dou you make game like tetris?

What I mean is how do you setup and control game board. As GD is “freeform” engine, not tile-based, there aren’t any tools built-in to manipulate game board (which would allow e.g. for easily clearing lines.

Round everything to a number (e.g. 40) and then bam you have everything on a 40 x 40 grid. You can then clear lines and stuff easily. You can use Floor(x), Ceil(x) to do this kind of stuff.