The AROW chunk describes an arrowhead pattern.  DR2D open polygons
(OPLY) can have arrowheads attached to their endpoints.  See the
description of the OPLY chunk later in this article for more
information on the OPLY chunk.

    #define ARROW_FIRST  0x01 /* Draw an arrow on the OPLY's first point */
    #define ARROW_LAST   0x02 /* Draw an arrow on the OPLY's last point */

    struct AROWstruct {
        ULONG       ID;
        ULONG       Size;
        UBYTE       Flags;          /* Flags, from ARROW_*, above */
        UBYTE       Pad0;           /* Should always 0 */
        USHORT      ArrowID;        /* Name of the arrow head */
        USHORT      NumPoints;
        IEEE        ArrowPoints[NumPoints*2];
    };

The Flags field specifies which end(s) of an OPLY to place an
arrowhead based on the #defines above.  ArrowID is the number by which
an OPLY will reference this arrowhead pattern.

The coordinates in the array ArrowPoints[] define the arrowhead's
shape.  These points form a closed polygon.  See the section on the
OPLY/CPLY object chunks for a descriptionof how DR2D defines shapes.
The arrowhead is drawn in the same coordinate system relative to the
endpoint of the OPLY the arrowhead is attached to.  The arrowhead's
origin (0,0) coincides with the OPLY's endpoint.  DR2D assumes that
the arrowhead represented in the AROW chunk is pointing to the right
so the proper rotation can be applied to the arrowhead.  The arrow is
filled according to the current fill pattern set in the ATTR object
attribute chunk.