The shape interface is an interface for leaf nodes which export their appearance as (a set of) polygons. It does not have any interesting public methods.
Every object implementing the shape interface must also implement the object interface and the node interface. No object implementing the shape interface is allowed to implement any of the container or mask interfaces.
void * vcl_shape_polygonize (void * obj, void * it, double delta, const struct geom_transform *t, const struct geom_rectangle *bbox, u8 ** buff, uns * buff_len, uns *closed, uns *points, uns hints)
This method is requested for expressing a part of the area occupied by
obj by one polygon (or polyline). This function is supposed to
be called in an iterative way – in every call one polygon/polyline is
returned. In first call, the
it argument should be
NULL, and next calls
it set to the return value of the previous call. If the return
value is NULL, then there should be no other calls. All iterations must
be done (there is no way to escape during the cycle).
delta argument means the precision of the approximation. The
t argument is
the required transformation from the
obj's coordinate system to pixel
coordinate system (the primary transformation matrix). The
bbox argument is the bounding box
of caller's area of interest – anything out of it is not required to be
approximated within the given precision, but must have a correct connection
to the next point inside the bounding box. Any polygons/polylines which are entirely outside
bbox can be skipped.
bbox is in
buff_len arguments are for point buffer – if the
buffer is small (or
NULL), then the callee is responsible for reallocating
xrealloc and update the value in
*buff_len, which is the buffer size in bytes. The caller can give
some hints using the
hints argument, but the callee can ignore them. The hints
are the following flags:
VCL_SHAPE_CLOSED_ONLY – the callee can skip polylines,
VCL_SHAPE_OPEN_ONLY – the callee can skip polygons.
Polygons/polylines are returned using an array of
geom_rectangle stored in the buffer, the number of points is returned in
*closed indicates whether the returned object is
a polygon (=1) or a polyline (=0).