diagram: share the rotate-translate calculation in the generic diagram class

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

diff --git a/src/flexagon/hexaflexagon_diagram.py b/src/flexagon/hexaflexagon_diagram.py
index 1a1cdff..4bb029b 100755 (executable)
--- a/src/flexagon/hexaflexagon_diagram.py
+++ b/src/flexagon/hexaflexagon_diagram.py
@@ -17,7 +17,7 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-from math import sin, cos, pi
+from math import cos, pi
 from .trihexaflexagon import TriHexaflexagon
 
 
@@ -88,59 +88,8 @@ class HexaflexagonDiagram(object):
         dest_x, dest_y = self.get_triangle_center_in_plan(triangle)
         theta = triangle.get_angle_in_plan_relative_to_hexagon()
 
-        # The transformation from a triangle in the hexagon to the correspondent
-        # triangle in the plan is composed by these steps:
-        #
-        #   1. rotate by 'theta' around (src_x, src_y);
-        #   2. move to (dest_x, dest_y).
-        #
-        # Step 1 can be expressed by these sub-steps:
-        #
-        #  1a. translate by (-src_x, -src_y)
-        #  1b. rotate by 'theta'
-        #  1c. translate by (src_x, src_y)
-        #
-        # Step 2. can be expressed by a translation like:
-        #
-        #  2a. translate by (dest_x - src_x, dest_y - src_y)
-        #
-        # The consecutive translations 1c and 2a can be easily combined, so
-        # the final steps are:
-        #
-        #  T1 -> translate by (-src_x, -src_y)
-        #  R  -> rotate by 'theta'
-        #  T2 -> translate by (dest_x, dest_y)
-        #
-        # Using affine transformations these are expressed as:
-        #
-        #      | 1  0  -src_x |
-        # T1 = | 0  1  -src_y |
-        #      | 0  0       1 |
-        #
-        #      | cos(theta)  -sin(theta)  0 |
-        # R  = | sin(theta)   con(theta)  0 |
-        #      |          0            0  1 |
-        #
-        #      | 1  0  dest_x |
-        # T2 = | 0  1  dest_y |
-        #      | 0  0       1 |
-        #
-        # Composing these transformations into one is achieved by multiplying
-        # the matrices from right to left:
-        #
-        #   T = T2 * R * T1
-        #
-        # NOTE: To remember this think about composing functions: T2(R(T1())),
-        # the inner one is performed first.
-        #
-        # The resulting  T matrix is the one below.
-        matrix = [
-            cos(theta), -sin(theta), -src_x * cos(theta) + src_y * sin(theta) + dest_x,
-            sin(theta),  cos(theta), -src_x * sin(theta) - src_y * cos(theta) + dest_y,
-                     0,           0,                                                 1
-        ]
-
-        return matrix
+        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: