NAME                                                              (V36)
	CreateUpfrontHookLayer -- Create a new layer on top of existing layers,
	                          using supplied callback BackFill hook.

    SYNOPSIS
	result = CreateUpfrontHookLayer(li,bm,x0,y0,x1,y1,flags,hook,[,bm2])
	d0                              a0 a1 d0 d1 d2 d3   d4  a3   [ a2 ]

	struct Layer *CreateUpfrontHookLayer(struct Layer_Info *, struct BitMap *,
	    LONG, LONG, LONG, LONG, LONG, struct Hook *, ... );

    FUNCTION
	Create a new Layer of position and size (x0,y0)->(x1,y1)
	and place it on top of all other layers.
	Make this layer of type found in flags
	Install Layer->BackFill callback hook.
	if SuperBitMap, use bm2 as pointer to real SuperBitMap.
	and copy contents of Superbitmap into display layer.

	Note: when using SUPERBITMAP, you should also set LAYERSMART flag.

    INPUTS
	li - pointer to LayerInfo structure
	bm - pointer to common BitMap used by all Layers
	x0,y0 - upper left hand corner of layer
	x1,y1 - lower right hand corner of layer
	flags - various types of layers supported as bit sets.
	hook -  Layer->BackFill callback Hook (see InstallLayerHook())

	        If hook is LAYERS_BACKFILL, the default backfill is
	        used for the layer.  (Same as pre-2.0)

	        As of V39:
		If hook is LAYERS_NOBACKFILL, the layer will not be
	        backfilled (NO-OP).

	bm2 - pointer to optional Super BitMap

    RESULTS
	result - pointer to Layer structure if successful
	         NULL if not successful

    BUGS

    SEE ALSO
	InstallLayerHook(), DeleteLayer(), graphics/layers.h, graphics/clip.h,
	graphics/gfx.h, utility/hooks.h