struct Layer
{
Bitmap; /* Bitmap.cache!=0 ==> layer */
Layer *next; /* next layer from front to back */
Cover *cover; /* layer etc. from which this is derived */
int user; /* a place for the user to stick stuff */
Lvis vis; /* visibility state */
};
struct Cover
{
Layer *layer; /* layer on which these are painted */
Layer *front; /* first sublayer */
Bitmap *ground; /* background texture */
};