Display a numpy array in Kivy

Question

first of all, I'm totally new to kivy, so I'm struggling a bit.

I'm trying to display a numpy array in a kivy window. So far i figured out that this should work using the Texture Class (http://kivy.org/docs/api-kivy.graphics.texture.html).

As my numpy array changes from time to time, I'm trying to adjust the following code to my application.

# create a 64x64 texture, defaults to rgb / ubyte
texture = Texture.create(size=(64, 64))

# create 64x64 rgb tab, and fill with values from 0 to 255
# we'll have a gradient from black to white
size = 64 * 64 * 3
buf = [int(x * 255 / size) for x in range(size)]

# then, convert the array to a ubyte string
buf = b''.join(map(chr, buf))

# then blit the buffer
texture.blit_buffer(buf, colorfmt='rgb', bufferfmt='ubyte')

# that's all ! you can use it in your graphics now :)
# if self is a widget, you can do this
with self.canvas:
    Rectangle(texture=texture, pos=self.pos, size=(64, 64))

It seems that creating the texture and changing it works as it should, but i dont get, how to display the texture.

Can anybody explain to me, how to use the

with self.canvas:
    Rectangle(texture=texture, pos=self.pos, size=(64, 64))

in a way, that I get to see my picture/numpy array.

Thanks alot in advance! Holzroller

Edit: I figured out that using Kivy 1.8.0 and the Texture Class is a bit messy. So I upgraded to Kivy 1.9.0 via github (installing Kivy via apt-get in Ubuntu 14.04 LTS serves you the 1.8.0 version) and I get to see the Texture using the following code. I hope that helps people who are having the same problem as me.

from kivy.graphics.texture import Texture
from kivy.graphics import Rectangle
from kivy.uix.widget import Widget
from kivy.base import runTouchApp
from array import array
from kivy.core.window import Window


# create a 64x64 texture, defaults to rgb / ubyte
texture = Texture.create(size=(1280, 1024), colorfmt='rgb')

# create 64x64 rgb tab, and fill with values from 0 to 255
# we'll have a gradient from black to white
size = 1280 * 1024 * 3
buf = [int(x * 255 / size) for x in range(size)]

# then, convert the array to a ubyte string
arr = array('B', buf)
# buf = b''.join(map(chr, buf))

# then blit the buffer
texture.blit_buffer(arr, colorfmt='rgb', bufferfmt='ubyte')

# that's all ! you can use it in your graphics now :)
# if self is a widget, you can do this
root = Widget()
with root.canvas:
    Rectangle(texture=texture, pos=(0, 0), size=(1280*3, 1024*3))

runTouchApp(root)

Edit2: Basically I'm back to the original Problem: I have a numpy array (type 'numpy.ndarray'; dtype 'uint8') and I'm trying to convert it into a format, so that the texture will show me the image. I tried to break it down to the same way it is done in the example code i posted above. But i sadly doesn't work. I really do not know what I'm doing wrong here. (my numpy array is called im2 in the folling code)

list1 = numpy.array(im2).reshape(-1,).tolist()

arr = array('B', list1)

texture.blit_buffer(arr, colorfmt='rgb', bufferfmt='ubyte')

Answer 1

Numpy have a tostring() attribute, that you could use directly, if the source array is uint8 type. You don't even need to reshape:

texture = Texture.create(size=(16, 16), colorfmt="rgb"))
arr = numpy.ndarray(shape=[16, 16, 3], dtype=numpy.uint8)
# fill your numpy array here
data = arr.tostring()
texture.blit_buffer(data, bufferfmt="ubyte", colorfmt="rgb"

About the issue you're talking in the comment, i see 2 points:

1. Ensure the callback from the ROS is called in the mainthread. Maybe the update is simply ignored.
2. When you manually change inplace the texture, the associated object that use it are not notified, you need to do it. Add a self.canvas.ask_update() to ensure the canvas redisplay at the next frame.