Add clockwise=False option to control outermost contour direction

Fixes #30

src/python/pathops/_pathops.pxd

@@ -158,7 +158,12 @@ cdef class Path:
 
     cpdef reverse(self)
 
-    cpdef simplify(self, bint fix_winding=*, bint keep_starting_points=*)
+    cpdef simplify(
+        self,
+        bint fix_winding=*,
+        bint keep_starting_points=*,
+        bint clockwise=*,
+    )
 
     cpdef convertConicsToQuads(self, float tolerance=*)
 
@@ -279,7 +284,7 @@ cdef int path_is_inside(const SkPath& self, const SkPath& other) except -1
 cpdef int restore_starting_points(Path path, list points) except -1
 
 
-cpdef bint winding_from_even_odd(Path path, bint truetype=*) except False
+cpdef bint winding_from_even_odd(Path path, bint clockwise=*) except False
 
 
 cdef list _decompose_quadratic_segment(tuple points)
@@ -309,10 +314,16 @@ cpdef Path op(
     SkPathOp operator,
     bint fix_winding=*,
     bint keep_starting_points=*,
+    bint clockwise=*,
 )
 
 
-cpdef Path simplify(Path path, bint fix_winding=*, bint keep_starting_points=*)
+cpdef Path simplify(
+    Path path,
+    bint fix_winding=*,
+    bint keep_starting_points=*,
+    bint clockwise=*,
+)
 
 
 cdef class OpBuilder:
@@ -321,6 +332,7 @@ cdef class OpBuilder:
     cdef bint fix_winding
     cdef bint keep_starting_points
     cdef list first_points
+    cdef bint clockwise
 
     cpdef add(self, Path path, SkPathOp operator)
 

src/python/pathops/_pathops.pyx

@@ -345,14 +345,19 @@ cdef class Path:
             skpath.addPath(contour.path)
         self.path = skpath
 
-    cpdef simplify(self, bint fix_winding=True, bint keep_starting_points=True):
+    cpdef simplify(
+        self,
+        bint fix_winding=True,
+        bint keep_starting_points=True,
+        bint clockwise=False,
+    ):
         cdef list first_points
         if keep_starting_points:
             first_points = self.firstPoints
         if not Simplify(self.path, &self.path):
             raise PathOpsError("simplify operation did not succeed")
         if fix_winding:
-            winding_from_even_odd(self)
+            winding_from_even_odd(self, clockwise)
         if keep_starting_points:
             restore_starting_points(self, first_points)
 
@@ -1116,23 +1121,23 @@ DEF DEBUG_WINDING = False
 
 @cython.wraparound(False)
 @cython.boundscheck(False)
-cpdef bint winding_from_even_odd(Path path, bint truetype=False) except False:
+cpdef bint winding_from_even_odd(Path path, bint clockwise=False) except False:
     """ Take a simplified path (without overlaps) and set the contours
     directions according to the non-zero winding fill type.
     The outermost contours are set to counter-clockwise direction, unless
-    'truetype' is True.
+    'clockwise' is True.
     """
     # TODO re-enable this once the new feature is stabilized in upstream skia
     # https://github.com/fonttools/skia-pathops/issues/10
     # if AsWinding(path.path, &path.path):
-    #     if path.clockwise ^ truetype:
+    #     if path.clockwise ^ clockwise:
     #         path.reverse()
     #     return True
     #
     # # in the unlikely event the built-in method fails, try our naive approach
 
     cdef int i, j
-    cdef bint inverse = not truetype
+    cdef bint inverse = not clockwise
     cdef bint is_clockwise, is_even
     cdef Path contour, other
 
@@ -1375,7 +1380,8 @@ cpdef Path op(
     Path two,
     SkPathOp operator,
     bint fix_winding=True,
-    bint keep_starting_points=True
+    bint keep_starting_points=True,
+    bint clockwise=False,
 ):
     cdef list first_points
     if keep_starting_points:
@@ -1384,32 +1390,43 @@ cpdef Path op(
     if not Op(one.path, two.path, operator, &result.path):
         raise PathOpsError("operation did not succeed")
     if fix_winding:
-        winding_from_even_odd(result)
+        winding_from_even_odd(result, clockwise)
     if keep_starting_points:
         restore_starting_points(result, first_points)
     return result
 
 
-cpdef Path simplify(Path path, bint fix_winding=True, bint keep_starting_points=True):
+cpdef Path simplify(
+    Path path,
+    bint fix_winding=True,
+    bint keep_starting_points=True,
+    bint clockwise=False,
+):
     cdef list first_points
     if keep_starting_points:
         first_points = path.firstPoints
     cdef Path result = Path()
     if not Simplify(path.path, &result.path):
         raise PathOpsError("operation did not succeed")
     if fix_winding:
-        winding_from_even_odd(result)
+        winding_from_even_odd(result, clockwise)
     if keep_starting_points:
         restore_starting_points(result, first_points)
     return result
 
 
 cdef class OpBuilder:
 
-    def __init__(self, bint fix_winding=True, bint keep_starting_points=True):
+    def __init__(
+        self,
+        bint fix_winding=True,
+        bint keep_starting_points=True,
+        bint clockwise=False,
+    ):
         self.fix_winding = fix_winding
         self.keep_starting_points = keep_starting_points
         self.first_points = []
+        self.clockwise = clockwise
 
     cpdef add(self, Path path, SkPathOp operator):
         self.builder.add(path.path, operator)
@@ -1421,7 +1438,7 @@ cdef class OpBuilder:
         if not self.builder.resolve(&result.path):
             raise PathOpsError("operation did not succeed")
         if self.fix_winding:
-            winding_from_even_odd(result)
+            winding_from_even_odd(result, self.clockwise)
         if self.keep_starting_points:
             restore_starting_points(result, self.first_points)
         return result

src/python/pathops/operations.py

@@ -19,13 +19,20 @@ def _draw(contours):
     return path
 
 
-def union(contours, outpen, fix_winding=True, keep_starting_points=True):
+def union(
+    contours,
+    outpen,
+    fix_winding=True,
+    keep_starting_points=True,
+    clockwise=False,
+):
     if not contours:
         return
     path = _draw(contours)
     path.simplify(
         fix_winding=fix_winding,
-        keep_starting_points=keep_starting_points
+        keep_starting_points=keep_starting_points,
+        clockwise=clockwise,
     )
     path.draw(outpen)
 
@@ -37,10 +44,18 @@ def _do(
     outpen,
     fix_winding=True,
     keep_starting_points=True,
+    clockwise=False,
 ):
     one = _draw(subject_contours)
     two = _draw(clip_contours)
-    result = op(one, two, operator, fix_winding, keep_starting_points)
+    result = op(
+        one,
+        two,
+        operator,
+        fix_winding=fix_winding,
+        keep_starting_points=keep_starting_points,
+        clockwise=clockwise,
+    )
     result.draw(outpen)