enable_move for Lines

[sigbjorngrini]

Hi

Is it possible to move entire lines as one does with enable_move for a scatter point?

Regards,
Sigbjorn

[dmadeka]

@sigbjorngrini What would the behavior you expect be? I guess you could see the HandDraw as "moving" a line. We have an issue open for moving the markers of a line to change the data - is that what you mean?

[sigbjorngrini]

@dmadeka The thought is to be able to click and hold on a line and move it in x or y direction. I. e. that you add the same value to all x or y points for each point in the line. This would in effect change the data yes.

[dmadeka]

@sigbjorngrini This might be better done with the markers. For now, the workaround would be to put a Scatter on the points of the line (or one point) and do something like:

def observe_scatter_x_y(change):
    if change['name'] == 'x':
        line.x = line.x + change['new'] - change['old']
    else:
        line.y = line.y + change['new'] - change['old']

Does that work for you?

[sigbjorngrini]

@dmadeka Thank you for the suggestion. Since I want to move all points relative to the one I physically move, the observe function reruns for every change of scatter.x and scatter.y and my kernel crashes. I found out that I could use the drag on_drag events. Something like this works as intended.

import bqplot as bq
import numpy as np

xs = bq.LinearScale()
ys = bq.LinearScale()
x = np.arange(-10, 11)
x2 = np.arange(-10, 11)
y = -x ** 3
y2 = -x2 ** 3 + 100

line = bq.Lines(x=x, y=y, scales={'x': xs, 'y': ys}, colors=['red'])
line2 = bq.Lines(x=x2, y=y2, scales={'x': xs, 'y': ys}, colors=['blue'])
scatter = bq.Scatter(x=x, y=y, scales={'x': xs, 'y': ys}, colors=['red'], enable_move=True)
scatter2 = bq.Scatter(x=x2, y=y2, scales={'x': xs, 'y': ys}, colors=['blue'], enable_move=False, marker='cross')
xax = bq.Axis(scale=xs, label='x', grid_lines='solid')
yax = bq.Axis(scale=ys, orientation='vertical', tick_format='0.2f', label='y', grid_lines='solid')

fig = bq.Figure(marks=[line, line2, scatter, scatter2], axes=[xax, yax])
        
def drag_end(s, changes):
    line.x = line.x + changes['point']['x'] - line.x[changes['index']]
    line.y = line.y + changes['point']['y'] - line.y[changes['index']]
    scatter.x = line.x
    scatter.y = line.y
    line.opacities = [1]
    scatter.visible = True
    
def drag_start(s, changes):
    scatter.visible = False
    line.opacities = [0.3]
    
def drag(s, changes):
    line.x = line.x + changes['point']['x'] - line.x[changes['index']]
    line.y = line.y + changes['point']['y'] - line.y[changes['index']]
    scatter.x = line.x
    scatter.y = line.y

scatter.on_drag_end(drag_end)
scatter.on_drag(drag)
scatter.on_drag_start(drag_start)

fig

Now, you can move around the red curve. I could now make a general function for this and make all lines with scatter move so this works for me. Ideally I wouldn't need the markers though.

[dmadeka]

@sigbjorngrini You could also move the line with one point right? Or is that too clunky? It would have less updating overhead. Or you could efficiently put them along your line? Maybe at every diadic partition?

[sigbjorngrini]

@dmadeka Yes that would work too. I'll see what I choose. That solved my problem. Thank you for your help.