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diff --git a/share/extensions/triangle.py b/share/extensions/triangle.py
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+#!/usr/bin/env python
+# coding=utf-8
+#
+# Copyright (C) 2007 John Beard john.j.beard@gmail.com
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+#
+"""
+This extension allows you to draw a triangle given certain information
+ about side length or angles.
+
+Measurements of the triangle
+
+ C(x_c,y_c)
+ /`__
+ / a_c``--__
+ / ``--__ s_a
+ s_b / ``--__
+ /a_a a_b`--__
+ /--------------------------------``B(x_b, y_b)
+ A(x_a,y_a) s_b
+"""
+
+import sys
+from math import acos, asin, cos, pi, sin, sqrt
+
+import inkex
+
+X, Y = range(2)
+
+def draw_SVG_tri(point1, point2, point3, offset, width, name, parent):
+ style = {'stroke': '#000000', 'stroke-width': str(width), 'fill': 'none'}
+ elem = parent.add(inkex.PathElement())
+ elem.update(**{
+ 'style': style,
+ 'inkscape:label': name,
+ 'd': 'M ' + str(point1[X] + offset[X]) + ',' + str(point1[Y] + offset[Y]) +
+ ' L ' + str(point2[X] + offset[X]) + ',' + str(point2[Y] + offset[Y]) +
+ ' L ' + str(point3[X] + offset[X]) + ',' + str(point3[Y] + offset[Y]) +
+ ' L ' + str(point1[X] + offset[X]) + ',' + str(point1[Y] + offset[Y]) + ' z'})
+ return elem
+
+
+def angle_from_3_sides(a, b, c): # return the angle opposite side c
+ cosx = (a * a + b * b - c * c) / (2 * a * b) # use the cosine rule
+ return acos(cosx)
+
+
+def third_side_from_enclosed_angle(s_a, s_b, a_c): # return the side opposite a_c
+ c_squared = s_a * s_a + s_b * s_b - 2 * s_a * s_b * cos(a_c)
+ if c_squared > 0:
+ return sqrt(c_squared)
+ else:
+ return 0 # means we have an invalid or degenerate triangle (zero is caught at the drawing stage)
+
+
+def pt_on_circ(radius, angle): # return the x,y coordinate of the polar coordinate
+ x = radius * cos(angle)
+ y = radius * sin(angle)
+ return [x, y]
+
+
+def v_add(point1, point2): # add an offset to coordinates
+ return [point1[X] + point2[X], point1[Y] + point2[Y]]
+
+
+def is_valid_tri_from_sides(a, b, c): # check whether triangle with sides a,b,c is valid
+ return (a + b) > c and (a + c) > b and (b + c) > a and a > 0 and b > 0 and c > 0 # two sides must always be greater than the third
+ # no zero-length sides, no degenerate case
+
+
+def draw_tri_from_3_sides(s_a, s_b, s_c, offset, width, parent): # draw a triangle from three sides (with a given offset
+ if is_valid_tri_from_sides(s_a, s_b, s_c):
+ a_b = angle_from_3_sides(s_a, s_c, s_b)
+
+ a = (0, 0) # a is the origin
+ b = v_add(a, (s_c, 0)) # point B is horizontal from the origin
+ c = v_add(b, pt_on_circ(s_a, pi - a_b)) # get point c
+ c[1] = -c[1]
+
+ offx = max(b[0], c[0]) / 2 # b or c could be the furthest right
+ offy = c[1] / 2 # c is the highest point
+ offset = (offset[0] - offx, offset[1] - offy) # add the centre of the triangle to the offset
+
+ draw_SVG_tri(a, b, c, offset, width, 'Triangle', parent)
+ else:
+ inkex.errormsg('Invalid Triangle Specifications.')
+
+
+class Triangle(inkex.EffectExtension):
+ def add_arguments(self, pars):
+ pars.add_argument("--s_a", type=float, default=100.0, help="Side Length a")
+ pars.add_argument("--s_b", type=float, default=100.0, help="Side Length b")
+ pars.add_argument("--s_c", type=float, default=100.0, help="Side Length c")
+ pars.add_argument("--a_a", type=float, default=60.0, help="Angle a")
+ pars.add_argument("--a_b", type=float, default=30.0, help="Angle b")
+ pars.add_argument("--a_c", type=float, default=90.0, help="Angle c")
+ pars.add_argument("--mode", default='3_sides', help="Side Length c")
+
+ def effect(self):
+ tri = self.svg.get_current_layer()
+ offset = self.svg.namedview.center
+ self.options.s_a = self.svg.unittouu(str(self.options.s_a) + 'px')
+ self.options.s_b = self.svg.unittouu(str(self.options.s_b) + 'px')
+ self.options.s_c = self.svg.unittouu(str(self.options.s_c) + 'px')
+ stroke_width = self.svg.unittouu('2px')
+
+ if self.options.mode == '3_sides':
+ s_a = self.options.s_a
+ s_b = self.options.s_b
+ s_c = self.options.s_c
+ draw_tri_from_3_sides(s_a, s_b, s_c, offset, stroke_width, tri)
+
+ elif self.options.mode == 's_ab_a_c':
+ s_a = self.options.s_a
+ s_b = self.options.s_b
+ a_c = self.options.a_c * pi / 180 # in rad
+
+ s_c = third_side_from_enclosed_angle(s_a, s_b, a_c)
+ draw_tri_from_3_sides(s_a, s_b, s_c, offset, stroke_width, tri)
+
+ elif self.options.mode == 's_ab_a_a':
+ s_a = self.options.s_a
+ s_b = self.options.s_b
+ a_a = self.options.a_a * pi / 180 # in rad
+
+ if (a_a < pi / 2.0) and (s_a < s_b) and (s_a > s_b * sin(a_a)): # this is an ambiguous case
+ ambiguous = True # we will give both answers
+ else:
+ ambiguous = False
+
+ sin_a_b = s_b * sin(a_a) / s_a
+
+ if (sin_a_b <= 1) and (sin_a_b >= -1): # check the solution is possible
+ a_b = asin(sin_a_b) # acute solution
+ a_c = pi - a_a - a_b
+ error = False
+ else:
+ sys.stderr.write('Error:Invalid Triangle Specifications.\n') # signal an error
+ error = True
+
+ if not error and (a_b < pi) and (a_c < pi): # check that the solution is valid, if so draw acute solution
+ s_c = third_side_from_enclosed_angle(s_a, s_b, a_c)
+ draw_tri_from_3_sides(s_a, s_b, s_c, offset, stroke_width, tri)
+
+ if not error and ((a_b > pi) or (a_c > pi) or ambiguous): # we want the obtuse solution
+ a_b = pi - a_b
+ a_c = pi - a_a - a_b
+ s_c = third_side_from_enclosed_angle(s_a, s_b, a_c)
+ draw_tri_from_3_sides(s_a, s_b, s_c, offset, stroke_width, tri)
+
+ elif self.options.mode == 's_a_a_ab':
+ s_a = self.options.s_a
+ a_a = self.options.a_a * pi / 180 # in rad
+ a_b = self.options.a_b * pi / 180 # in rad
+
+ a_c = pi - a_a - a_b
+ s_b = s_a * sin(a_b) / sin(a_a)
+ s_c = s_a * sin(a_c) / sin(a_a)
+
+ draw_tri_from_3_sides(s_a, s_b, s_c, offset, stroke_width, tri)
+
+ elif self.options.mode == 's_c_a_ab':
+ s_c = self.options.s_c
+ a_a = self.options.a_a * pi / 180 # in rad
+ a_b = self.options.a_b * pi / 180 # in rad
+
+ a_c = pi - a_a - a_b
+ s_a = s_c * sin(a_a) / sin(a_c)
+ s_b = s_c * sin(a_b) / sin(a_c)
+
+ draw_tri_from_3_sides(s_a, s_b, s_c, offset, stroke_width, tri)
+
+
+if __name__ == '__main__':
+ Triangle().run()