add fixed size for arrow heads in Quiver Plot

[gurpreet3737]

While plotting two or more vectors using quiver plots arrows heads are scaled with respect to barb length. No option for having arrow heads of fixed size as depicted in attached file. Please add option for the same.Here is the code:

from plotly import tools
from plotly.offline import download_plotlyjs, plot, iplot, init_notebook_mode
import plotly.graph_objs as go
import plotly.figure_factory as ff
import numpy as np

init_notebook_mode(connected=True)

layout=go.Layout(xaxis=dict(range=[-10,10],dtick=1),
yaxis=dict(range=[-10,10],dtick=1, ticks='outside'),
width=900, height=900)

v=np.array([[1,1],[-2,2], [4,7]])
x, y = [0,0,0], [0,0,0]
fig= ff.create_quiver(x, y, v[:,0], v[:,1], scale=1)
fig.layout.update(layout)
iplot(fig)

[janosh]

Would unit-vectoring and then multiplying the barbs end_x and end_y each by sqrt(fixed_size) in get_barbs be an acceptable implementation?

plotly.py/packages/python/plotly/plotly/figure_factory/_quiver.py

Lines 177 to 197 in ce0ed07

	def get_barbs(self):
	"""
	Creates x and y startpoint and endpoint pairs
	After finding the endpoint of each barb this zips startpoint and
	endpoint pairs to create 2 lists: x_values for barbs and y values
	for barbs
	:rtype: (list, list) barb_x, barb_y: list of startpoint and endpoint
	x_value pairs separated by a None to create the barb of the arrow,
	and list of startpoint and endpoint y_value pairs separated by a
	None to create the barb of the arrow.
	"""
	self.end_x = [i + j for i, j in zip(self.x, self.u)]
	self.end_y = [i + j for i, j in zip(self.y, self.v)]
	empty = [None] * len(self.x)
	barb_x = utils.flatten(zip(self.x, self.end_x, empty))
	barb_y = utils.flatten(zip(self.y, self.end_y, empty))
	return barb_x, barb_y