Refactor pnpoly function in Cython and add to shared package

skimage/_shared/geometry.pxd

@@ -0,0 +1,7 @@
+
+cdef inline unsigned char point_in_polygon(int nr_verts, double *xp, double *yp,
+                                           double x, double y)
+
+cdef void points_in_polygon(int nr_verts, double *xp, double *yp,
+                            int nr_points, double *x, double *y,
+                            unsigned char *result)

skimage/_shared/geometry.pyx

@@ -0,0 +1,27 @@
+#cython: cdivison=True
+#cython: boundscheck=False
+#cython: nonecheck=False
+#cython: wraparound=False
+
+
+cdef inline unsigned char point_in_polygon(int nr_verts, double *xp, double *yp,
+                                           double x, double y):
+    cdef int i
+    cdef unsigned char c = 0
+    cdef int j = nr_verts - 1
+    for i in range(nr_verts):
+        if (
+            (((yp[i] <= y) and (y < yp[j])) or
+            ((yp[j] <= y) and (y < yp[i])))
+            and (x < (xp[j] - xp[i]) * (y - yp[i]) / (yp[j] - yp[i]) + xp[i])
+        ):
+            c = not c
+        j = i
+    return c
+
+cdef void points_in_polygon(int nr_verts, double *xp, double *yp,
+                            int nr_points, double *x, double *y,
+                            unsigned char *result):
+    cdef int n
+    for n in range(nr_points):
+        result[n] = point_in_polygon(nr_verts, xp, yp, x[n], y[n])

skimage/_shared/setup.py

@@ -13,9 +13,11 @@ def configuration(parent_package='', top_path=None):
     config = Configuration('_shared', parent_package, top_path)
     config.add_data_dir('tests')
 
+    cython(['geometry.pyx'], working_path=base_path)
     cython(['interpolation.pyx'], working_path=base_path)
     cython(['transform.pyx'], working_path=base_path)
 
+    config.add_extension('geometry', sources=['geometry.c'])
     config.add_extension('interpolation', sources=['interpolation.c'],
                          include_dirs=[get_numpy_include_dirs()])
     config.add_extension('transform', sources=['transform.c'],