How can I program an RDK using inline JavaScript?

jtdeakin

Hi,

I have a task which using random dot kinematograms (moving dots) in OpenSesame which contains inline python script to create and move the dots. I can’t run this online because of the Python script. The only information I can find says you can’t use inline JavaScript to create canvas objects. Where would I begin when trying to make this experiment run online?

Thanks

sebastiaan

Hi @jtdeakin ,

You can implement this with some creativity 😉 Generating random-dot stimuli in JavaScript won't be possible, but you can generate them offline with Python and then save them as images. Next, you store these images in the file pool, and play them back as an animation by putting a sketchpad inside a loop. (There is a practical limit of about 1000 files in the file pool though. Beyond that browsers start to complain.)

Saving a frame from a psychopy DotStim , which I assume you're using, isn't trivial, but you can do it by accessing its _verticesBase property like so:

from PIL import Image, ImageDraw
import os
import itertools

SIZE = 200
DOTSIZE = 3

dots.draw()  # assumption: dots is a psychopy.visual.DotStim
im = Image.new('1', (SIZE, SIZE))
dr = ImageDraw.Draw(im)
for x, y in dots._verticesBase:
    for dx, dy in itertools.product(range(DOTSIZE), range(DOTSIZE)):
        xdx = int(x) + dx + SIZE // 2
        ydy = int(y) + dy + SIZE // 2
        if xdx >= SIZE or ydy >= SIZE:
            continue
        dr.point((xdx, ydy), fill='white')
im.save('my_dot_stim.png')

Hope this helps!

Sebastiaan

jtdeakin

Thanks Sebastiaan, that is really helpful!