NAME
    ScrollLayer -- Scroll around in a superbitmap, translate coordinates
                  in non-superbitmap layer.

SYNOPSIS
    ScrollLayer( dummy, l, dx, dy )
                 a0     a1 d0  d1

    void ScrollLayer( LONG, struct Layer *, LONG, LONG);

FUNCTION
    For a SuperBitMap Layer:
    Update the SuperBitMap from the layer display, then copy bits
    between Layer and SuperBitMap to reposition layer over different
    portion of SuperBitMap.
    For nonSuperBitMap layers, all (x,y) pairs are adjusted by
    the scroll(x,y) value in the layer.  To cause (0,0) to actually
    be drawn at (3,10) use ScrollLayer(-3,-10). This can be useful
    along with InstallClipRegion to simulate Intuition GZZWindows
    without the overhead of an extra layer.

INPUTS
    dummy - unused
    l - pointer to a layer
    dx - delta to add to current x scroll value
    dy - delta to add to current y scroll value

BUGS
    May not handle (dx,dy) which attempts to move the layer ouside the
    layer's SuperBitMap bounds.

SEE ALSO
    graphics/layers.h