A DR2D project is broken up into one or more layers.  Each DR2D object
is in one of these layers.  Layers provide several useful features.
Any particular layer can be "turned off", so that the objects in the
layer are not displayed.  This eliminates the unnecessary display of
objects not currently needed on the screen.  Also, the user can lock a
layer to protect the layer's objects from accidental changes.

    struct LAYRstruct {
        ULONG    ID;
        ULONG    Size;
        USHORT   LayerID;              /* ID of the layer */
        char     LayerName[16];        /* Null terminated and padded */
        UBYTE    Flags;                /* Flags, from LF_*, below */
        UBYTE    Pad0;                 /* Always 0 */
    };

LayerID is the number assigned to this layer.  As the field's name
indicates, LayerName[] is the NULL terminated name of the layer.
Flags is a bit field who's bits are set according to the #defines
below:

    #define LF_ACTIVE       0x01    /* Active for editing */
    #define LF_DISPLAYED    0x02    /* Displayed on the screen */

If the LF_ACTIVE bit is set, this layer is unlocked.  A set
LF_DISPLAYED bit indicates that this layer is currently visible on the
screen.  A cleared LF_DISPLAYED bit implies that LF_ACTIVE is not set.
The reason for this is to keep the user from accidentally editing
layers that are invisible.