[PD] Gem render out of the screen (and v4l2loopback)

Simon Wise simonzwise at gmail.com
Tue Mar 3 06:03:06 CET 2015

On 03/03/15 10:58, Olivier Baudu wrote:
> Hi list,
> Until now, and as far as I (think I) can remember, GEM was rendering frames even
> if the window (with or without border) was :
> - out of the screen
> - reduce in the tool-bar
> - hidden by an other window
> The last time I use this property was on an Ubuntu 13.10 both with "pd-vanilla +
> gem from the depot" and " pd-extended" (but I can't give you versions...
> because... well, I don't know them... sorry)
> On several different patches, I recorded GEM content (which was not display on
> my desktop because of "offset" option) with the combo [pix_record] /
> v4l2loopback in order to make a "fake webcam" to stream.
> It was working.
> It is still working on computers where those patches where installed.
> Now, I am on Ubuntu 14.04 / GEM: 0.93.3 and if anything is put over the GEM
> content, it seems to be that none of the pixel "under" is rendered.
> If I open the v4l2loopback device on VLC (or whatever) and hide part of the GEM
> window (even by dragging icons from my desktop), those parts are not refresh
> anymore.
> Does GEM change its way to render ?
> Is the Ubuntu 14.04 display different ?
> Do I misunderstood something ?

I don't know the answers to those questions ... it could be optimisation at one 
of several levels ... but in very many use-cases not rendering content that is 
covered would be a good thing, and a big improvement to performance.

In that case setting up a virtual X display without a monitor may be the answer, 
though depending on what you are doing it could make a difference to what is 
hardware accelerated.

It was some time ago that I last did that, but will look up the method, 
essentially it involves launching a new X-server instance and running pd with 
its DISPLAY env set to that display.


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