add contour.setStartPoint + test (#668)

Lib/fontParts/base/contour.py

@@ -957,6 +957,45 @@ def _removePoint(self, index, preserveCurve, **kwargs):
         """
         self.raiseNotImplementedError()
 
+    def setStartPoint(self, point):
+        """
+        Set the first point on the contour.
+        point can be a segment object or an index.
+        """
+        if self.open:
+            raise FontPartsError("An open contour can not change the starting point.")
+
+        points = self.points
+        if not isinstance(point, int):
+            pointIndex = points.index(point)
+        else:
+            pointIndex = point
+        if pointIndex == 0:
+            return
+
+        if pointIndex >= len(points):
+            raise ValueError(("The contour does not contain a point "
+                              "at index %d" % pointIndex))
+        self._setStartPoint(pointIndex)
+
+    def _setStartPoint(self, pointIndex, **kwargs):
+        """
+        Subclasses may override this method.
+        """
+        points = self.points
+        points = points[pointIndex:] + points[:pointIndex]
+        # Clear the points.
+        for point in self.points:
+            self.removePoint(point)
+        # Add the points.
+        for point in points:
+            self.appendPoint(
+                (point.x, point.y),
+                type=point.type,
+                smooth=point.smooth,
+                name=point.name,
+                identifier=point.identifier
+            )
     # ---------
     # Selection
     # ---------

Lib/fontParts/test/test_contour.py

@@ -669,3 +669,20 @@ def test_segment_insert_curve_closed(self):
             [(point.x, point.y) for point in contour.points],
             [(0, 0), (2, 2), (3, 3), (4, 4), (1, 1), (5, 5)]
         )
+
+    # ------
+    # points
+    # ------
+
+    def test_setStartPoint(self):
+        contour, _ = self.objectGenerator("contour")
+        contour.appendPoint((0, 0), "line")
+        contour.appendPoint((1, 1), "line")
+        contour.appendPoint((2, 2), "line")
+        contour.appendPoint((3, 3), "line")
+
+        contour.setStartPoint(2)
+        self.assertEqual(
+            [(point.x, point.y) for point in contour.points],
+            [(2, 2), (3, 3), (0, 0), (1, 1)]
+        )