NAME
    WhichLayer -- Which Layer is this point in?

SYNOPSIS
    layer = WhichLayer( li, x, y )
    d0                  a0  d0 d1

    struct Layer *WhichLayer(struct Layer_Info*, WORD, WORD);

FUNCTION
    Starting at the topmost layer check to see if this point (x,y)
        occurs in this layer.  If it does return the pointer to this
        layer. Return NULL if there is no layer at this point.

INPUTS
    li  = pointer to LayerInfo structure
    (x,y) = coordinate in the BitMap

RESULTS
    layer - pointer to the topmost layer that this point is in
            NULL if this point is not in a layer

SEE ALSO
    graphics/layers.h