examples/vector.py

   1 from math import pi, sin, cos
   2 from pyx import *
   3
   4 def vector(x1, y1, x2, y2, t, pos=0.5, distance=0.1):
   5     c = canvas.canvas()
   6     c.stroke(path.line(x1, y1, x2, y2), [deco.earrow.normal])
   7     textbox = text.text((1-pos)*x1 + pos*x2, (1-pos)*y1 + pos*y2, t,
   8                         [text.halign.center, text.vshift.mathaxis])
   9     if distance < 0:
  10         textbox.linealign(-distance, y1 - y2, x2 - x1)
  11     else:
  12         textbox.linealign(distance, y2 - y1, x1 - x2)
  13     c.insert(textbox)
  14     return c
  15
  16 r = 1.5
  17 a = 150
  18
  19 c = canvas.canvas()
  20 dx, dy = cos(a * pi / 180), sin(a * pi / 180)
  21 x, y = r * dx, r * dy
  22 c.stroke(path.circle(0, 0, r))
  23 c.insert(vector(0, 0, x, y, r"$\vec r$"))
  24 c.insert(vector(x, y, x - dy, y + dx, r"$\vec t$", pos=0.7))
  25 c.insert(vector(x, y, x + dx, y + dy, r"$\vec n$", pos=0.7))
  26 c.writeEPSfile("vector")