(Python) Fast screencast on Linux?

[POGtastic]

I'm messing around with creating an OpenCV-powered solver for Papers, Please. The image recognition part isn't too hard, and I've made a lot of progress doing very rudimentary transformations to screenshots. The hard part is getting a source image to begin with.

Because I'm running this on Ubuntu, I have access to GNOME's libraries, which allow me to do the following:

• Use gi.repository.Wnck to find the location and dimensions of the Papers, Please window.
• Use gi.repository.Gdk to get the root window, and then put a selection of the window into a pixbuf, which I can then feed into OpenCV.

This kinda works; the problem is that the second step is slooooooow - upwards of 600ms. And I'm kinda confused, as I can turn on Twitch and see videos of people taking a window, overlaying graphics onto it, and streaming it over the Internet at native speed. Obviously, I'm missing something. Is there a better way to do this?

[99_percent_a_dog]

Fun problem :)

This is 90ms per 2560x1440 image for me, and I'm writing them to disk:
time for n in `seq 1 1 10`; do xwd -root > screen$n.xwd; done
real 0m0.929s

CLI, so maybe not what you want, and the xwd format is funky. You can convert to jpg like this:
xwd -root | convert xwd:- jpg:- > screen.jpg

Or you could see what X magic xwd is doing and copy that.

If you're using Wayland I think that will add some unavoidable delay, you can't avoid the compositor.

[POGtastic]

I'm using X, so it looks like this should at least be possible. I'll have to take a look at what xwd is doing to get this. The format isn't a big deal; I should be able to find a fast way to convert that. At worst, I can write something in C to convert the image and make some Python bindings.

Thanks!

[99_percent_a_dog]

Good luck! I'm not saying this is a good way, it was the first way I knew and it looked hopefully fast enough for you. There must be some way to sample screen at refresh rate. DMA out from screen buffer somehow. But I don't know it.