Question

This question is similar to this one

Fastest method of screen capturing

but for linux/X11.

To be more specific, i need a method to capture the pixel images of one window (the programmatic equivalent of alt-print screen in windows) running on a X11 diplay.

Notes and requirements:

1) Even if a new window is placed on top of the window that is being captured, the pixel image should still point to the original application window without any occlusion

2) it is not needed that the application window to be seen by the user, i just need to store the pixel buffers/images for video purposes

other alternatives that i’ve explored are:

1) xvfb – it works but it does does CPU rendering, which is slow and
wasteful of a good GPU

2) x11 inside many lxc – theoretically could work but is complex to
setup, and i’m not sure it will scale well with many windows being
captured

suggestions and ideas are welcome

Answer 1

This is possible using VirtualGL in a server with hardware acceleration. Basically just configure the server appropiately, then either on the same machine or on a machine in the same network, run

export DISPLAY=<your xvfb display>
vglrun <your_app>

This will have the following advantages:

1) your app will render using virtualGL, which will use the hardware

2) VirtualGL will display your 3D context inside the Xfvb display, which will only render the 2D widgets in CPU

3) configure Xvfb to render to a framebuffer

4) profit!