README.md: mention also the tetraflexagon example

[flexagon-toolkit.git] / src / flexagon / hexaflexagon_diagram.py

diff --git a/src/flexagon/hexaflexagon_diagram.py b/src/flexagon/hexaflexagon_diagram.py
index 4bb029b..7b09c94 100755 (executable)
--- a/src/flexagon/hexaflexagon_diagram.py
+++ b/src/flexagon/hexaflexagon_diagram.py
@@ -43,6 +43,10 @@ class HexaflexagonDiagram(object):
         self.plan_origin = (self.x_border * 2. + self.hexagon_radius / 2.,
                             self.x_border + self.triangle_radius / 3.)
 
+        # The offset of the backfaces relative to the first hexagon
+        self.backfaces_offsets = (0,
+                                  (self.hexagon_radius + self.x_border) * 2)
+
         self.hexagons_color_map = [(1, 0, 0), (0, 1, 0), (0, 0, 1)]
 
     def _init_centers(self):
@@ -66,6 +70,15 @@ class HexaflexagonDiagram(object):
     def get_triangle_center(self, triangle):
         return self.triangles_centers[triangle.hexagon.index][triangle.index]
 
+    def get_triangle_center_in_backfaces(self, triangle):
+        """Get the center of this triangle but in the backface"""
+        x0, y0 = self.backfaces_offsets
+
+        backface_triangle_index = triangle.get_backface_index()
+        x, y = self.triangles_centers[triangle.hexagon.index][backface_triangle_index]
+
+        return x0 + x, y0 + y
+
     def get_triangle_center_in_plan(self, triangle):
         x0, y0 = self.plan_origin
         i, j = self.hexaflexagon.get_triangle_plan_position(triangle)
@@ -91,6 +104,18 @@ class HexaflexagonDiagram(object):
         return self.backend.calc_rotate_translate_transform(src_x, src_y,
                                                             dest_x, dest_y, theta)
 
+    def get_triangle_backfaces_transform(self, triangle):
+        """Calculate the transformation matrix from a triangle in an hexagon to
+        the correspondent triangle in a backface.
+
+        Return the matrix as a list of values sorted in row-major order."""
+        src_x, src_y = self.get_triangle_center(triangle)
+        dest_x, dest_y = self.get_triangle_center_in_backfaces(triangle)
+        theta = triangle.get_angle_in_backface_relative_to_hexagon()
+
+        return self.backend.calc_rotate_translate_transform(src_x, src_y,
+                                                            dest_x, dest_y, theta)
+
     def draw_hexagon_template(self, hexagon):
         for triangle in hexagon.triangles:
             cx, cy = self.get_triangle_center(triangle)