D545: Freestyle Python API: new methods for Stroke and StrokeVertexIterator.

This revision extends the Freestyle Python API to make for style module writing
easier.

- freestyle.types.Stroke: A proper support for reversed() is implemented.  It
works the same with other Python sequence objects (returns an iterator starting
from the end).  This is in effect equivalent to Stroke.stroke_vertices_end().

- freestyle.types.StrokeVertexIterator: An incremented, decremented and reversed
method are added.  The first two methods return a new StrokeVertexIterator
object that has been incremented and decremented, respectively. The reversed
method returns a new StrokeVertexIterator object that will traverse stroke
vertices in the opposite direction.

- freestyle.types.Interface0DIterator: Its constructor now accepts a Stroke
object to create an Interface0DIterator that traverses stroke vertices.  This is
in effect equivalent to Stroke.vertices_begin().  The new API makes stroke
shaders involving function calls much simpler as illustrated below:

  # in the old API
  it = stroke.stroke_vertices_begin()
  for vert in it:
      result = somefunc(Interface0DIterator(it))

  # in the new API
  it = Interface0DIterator(stroke)
  for vert in it:
      result = somefunc(it)


Differential Revision: https://developer.blender.org/D545

Reviewers: kjym3

source/blender/freestyle/intern/python/Interface1D/BPy_Stroke.cpp

@@ -286,6 +286,21 @@ static PyObject *Stroke_stroke_vertices_end(BPy_Stroke *self)
 	return BPy_StrokeVertexIterator_from_StrokeVertexIterator(sv_it, true);
 }
 
+PyDoc_STRVAR(Stroke_reversed_doc,
+	".. method:: __reversed__()\n"
+	"\n"
+	"   Returns a StrokeVertexIterator iterating over the vertices of the Stroke\n"
+	"   in the reversed order (from the last to the first).\n"
+	"\n"
+	"   :return: A StrokeVertexIterator pointing after the last StrokeVertex.\n"
+	"   :rtype: :class:`StrokeVertexIterator`");
+
+static PyObject *Stroke_reversed(BPy_Stroke *self)
+{
+	StrokeInternal::StrokeVertexIterator sv_it(self->s->strokeVerticesEnd());
+	return BPy_StrokeVertexIterator_from_StrokeVertexIterator(sv_it, true);
+}
+
 PyDoc_STRVAR(Stroke_stroke_vertices_size_doc,
 ".. method:: stroke_vertices_size()\n"
 "\n"
@@ -310,6 +325,7 @@ static PyMethodDef BPy_Stroke_methods[] = {
 	{"stroke_vertices_begin", (PyCFunction)Stroke_stroke_vertices_begin, METH_VARARGS | METH_KEYWORDS,
 	                          Stroke_stroke_vertices_begin_doc},
 	{"stroke_vertices_end", (PyCFunction)Stroke_stroke_vertices_end, METH_NOARGS, Stroke_stroke_vertices_end_doc},
+	{"__reversed__", (PyCFunction)Stroke_reversed, METH_NOARGS, Stroke_reversed_doc},
 	{"stroke_vertices_size", (PyCFunction)Stroke_stroke_vertices_size, METH_NOARGS, Stroke_stroke_vertices_size_doc},
 	{NULL, NULL, 0, NULL}
 };