Casey P Casey P - 9 days ago 6
Python Question

Bokeh: implementing custom javascript in an image plot

I am trying to combine these two examples in Bokeh:

http://bokeh.pydata.org/en/latest/docs/gallery/image.html
http://bokeh.pydata.org/en/latest/docs/user_guide/interaction.html#customjs-for-widgets

The idea seems simple. I want to plot the image shown in the first link and then vary the frequency of the sine function using an interactive slider:

import numpy as np

from bokeh.plotting import figure, show, output_file
from bokeh.models import CustomJS, ColumnDataSource, Slider
from bokeh.io import vform


N = 10

x = np.linspace(0, 10, N)
y = np.linspace(0, 10, N)
xx, yy = np.meshgrid(x, y)
d = np.sin(xx)*np.cos(yy)

output_file("image.html", title="image.py example")

source = ColumnDataSource(data={'d': d, 'x': x, 'y': y})

p = figure(x_range=[0, 10], y_range=[0, 10])
p.image([source.data['d']], x=[0], y=[0], dw=[10], dh=[10], palette="Spectral11")

callback = CustomJS(args=dict(source=source), code="""
var data = source.get('data');
var f = cb_obj.get('value')
x = data['x']
y = data['y']
d = data['d']
for (i = 0; i < x.length; i++) {
for (i = 0; i < x.length; i++){
d[i][j] = Math.sin(f*x[i])*Math.cos(y[j])
}
source.trigger('change');
""")

slider = Slider(start=0.1, end=4, value=1, step=.1, title="angular frequency", callback=callback)

layout = vform(slider, p)

show(layout)


The chart plots right, but the image never updates. The problem almost certainly exists how I am plotting the image:

p.image([source.data['d']], x=[0], y=[0], dw=[10], dh=[10], palette="Spectral11")


I don't think that's how you properly attach a plot to a source object. I am just passing in an array, which explains why the plot isn't updating when source changes, but I am not sure what the correct method is for the image function. If I change the statement to:

p.image(['d'], x=[0], y=[0], dw=[10], dh=[10], source=source, palette="Spectral11")


It won't plot correctly. I am not sure if this is just a syntax problem or a deeper issue. Any pointers would be appreciated. Thanks in advance.

Answer

I was dealing with a similar problem for a couple of days. Finally I make it work. First notice the brackets [] in the ColumnDataSource function. The data allows for multiple images. So, inside the callback function you use [0] to get the data for one image. Also the use of 'x' and 'y' in the source for the image conflicts with the location of the image x=[0], and y[0], so I used xx and yy. I want to mention that I borrowed from an example by tobyhodges color_sliders.py a way to push slider information to a callback function that has been already defined. Here my code that worked for me:

import numpy as np
from bokeh.plotting import figure, show, output_file
from bokeh.models import CustomJS, ColumnDataSource, Slider
from bokeh.io import vform

N = 100

x = np.linspace(0, 10, N)
y = np.linspace(0, 10, N)
xx, yy = np.meshgrid(x, y)
d = np.sin(xx)*np.cos(yy)  

output_file("image.html", title="image.py example")

source = ColumnDataSource(data={'d': [d], 'xx': [x], 'yy': [y]})

p = figure(x_range=[0, 10], y_range=[0, 10])
p.image(image="d", x=[0], y=[0], dw=[10], dh=[10], palette="Spectral11",source=source)

callback = CustomJS(args=dict(source=source), code="""
        var xx = source.get('data')['xx'][0];
        var yy = source.get('data')['yy'][0];
        var d = source.get('data')['d'][0];
        var f = slider.get('value');
        for (var i = 0; i < xx.length; i++) {
            for (var j = 0; j < yy.length; j++){
                d[i][j] = Math.sin(f * xx[i]) * Math.cos(yy[j]);
            }
        }
        source.trigger('change');
    """)

slider = Slider(start=0.1, end=4, value=1, step=.1, title="angular frequency", callback=callback)
callback.args['slider'] = slider
layout = vform(slider, p)
show(layout)

To avoid deprecation warnings in the latest version of bokeh (the version that I have just installed is 0.12.3) I have modified this code as follows. In this code, I don't use data source for the image. Inside CustomJS I pass the image handle "im" and get the data source as im.data_source.

import numpy as np
import bokeh
import bokeh.plotting

N = 100

x = np.linspace(0, 10, N)
y = np.linspace(0, 10, N)
xx, yy = np.meshgrid(x, y)
d = np.sin(xx)*np.cos(yy)  

source = bokeh.models.ColumnDataSource(data={'x': [x], 'y': [y]})

p = bokeh.plotting.figure(x_range=[0, 10], y_range=[0, 10])
im = p.image(image=[d], x=[0], y=[0], dw=[10], dh=[10], palette="Spectral11")

callback = bokeh.models.CustomJS(args=dict(source=source,im=im), code="""
        var x = source.data['x'][0];
        var y = source.data['y'][0];
        var image_source = im.data_source;
        var d = image_source.data['image'][0];
        var f = slider.value;
        for (var i = 0; i < x.length; i++) {
            for (var j = 0; j < y.length; j++){
                d[i][j] = Math.sin(f * x[i]) * Math.cos(f * y[j]);
            }
        }
        image_source.trigger('change');
    """)

slider = bokeh.models.Slider(start=0.1, end=4, value=1, step=.1, 
                             title="angular frequency", callback=callback)
callback.args['slider'] = slider
layout = bokeh.models.layouts.Column(slider, p)

bokeh.io.output_file("image.html", title="image.py example")
bokeh.io.save(layout)
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