import math
from inkex import EffectExtension, PathElement, transforms as T
# https://en.wikipedia.org/wiki/Rotations_and_reflections_in_two_dimensions
def reflection_matrix(theta):
theta2 = 2 * theta
return [
[math.cos(theta2), math.sin(theta2), 0],
[math.sin(theta2), -math.cos(theta2), 0],
]
def svg_matrix_order(mat):
((a, c, e), (b, d, f)) = mat
return a, b, c, d, e, f
class Flip(EffectExtension):
"""Extension to flip a path about the line from the start to end node"""
def effect(self):
for node in self.svg.selection.filter(PathElement).values():
points = list(node.path.end_points)
if len(points) < 2 or points[0] == points[-1]:
continue
start = points[0]
end = points[-1]
v = end - start
theta = math.atan2(v.y, v.x)
# transforms go in reverse order
mat = T.Transform()
mat.add_translate(start)
mat.add_matrix(*svg_matrix_order(reflection_matrix(theta)))
mat.add_translate(-start)
node.path = node.path.transform(mat)
if __name__ == '__main__':
Flip().run()
