function Snap(whichPiece) {
if (whichPiece._x>40 && whichPiece._x<320 && whichPiece._y>40 && whichPiece._y<320) {
var xSnapNumber = Math.floor((whichPiece._x-20)/40);
var ySnapNumber = Math.floor((whichPiece._y-20)/40);
if (((whichPiece._x-20)%40)/40<.5) {
whichPiece._x = xSnapNumber*40+20;
} else {
whichPiece._x = (xSnapNumber+1)*40+20;
}
if (((whichPiece._y-20)%40)/40<.5) {
whichPiece._y = ySnapNumber*40+20;
} else {
whichPiece._y = (ySnapNumber+1)*40+20;
}
}
}
这段代码怎样理由啊？

做这种“吸附”算法，要一下子考虑周全，得费点脑子