private synchronized Object[] stateid(Object... extra) {
Object[] ret = new Object[layers.size() + extra.length];
for (int i = 0; i < layers.size(); i++) {
Sprite spr = sprites.get(layers.get(i));
if (spr == null) ret[i] = null;
else ret[i] = spr.stateid();
}
for (int i = 0; i < extra.length; i++) ret[i + layers.size()] = extra[i];
return (ArrayIdentity.intern(ret));
}
