def motion(x1, y1):
global x0, y0, rotation, scale
if rotating:
p0 = screen2space(x0, y0)
p1 = screen2space(x1, y1)
rotation = q.product(rotation, q.arcball(*p0), q.arcball(*p1))
if scaling:
scale *= exp(((x1 - x0) - (y1 - y0)) * .01)
x0, y0 = x1, y1
glutPostRedisplay()
def arcball(_, p0, p1):
''' set the rotation only according to the arcball'''
_.rotation = _q.product(_.rotation, _q.arcball(*p0), _q.arcball(*p1))
_.matrix = _q.matrix(_.rotation)
'''
