[febvwdap] Chess thickness

For each position of a chess game, compute the number of moves, or proportion of moves, that do not lead to being checkmated.  Probably done by computers with MultiPV, but humans can help, too.  Depict that value over the course of a game.

Artistically attempts to capture the riskiness of a position.  Perhaps icons walking across a "floor" with thickness.  Probably also want to include moves which are very negative but the computer hasn't found mate:  Order moves top to bottom strongest to weakest and the color the opacity of the floor by the evaluation score.

The level of the floor could indicate current position evaluation, with "falls" for bad moves.

We can also speculate the future of a game in progress; the riskiness of the next several moves assuming optimal(ish) play.