[winswitch] Dynamically variable DPI?

Antoine Martin antoine at nagafix.co.uk
Fri Mar 17 18:01:13 GMT 2017

On 18/03/17 00:20, Timothy Hobbs via shifter-users wrote:
> Hi,
> I'm using xpra+subuser for most things now. It works well, except for
> full screen videos on my high-dpi display, which don't play well at all.
> All of this is local, and as far as I know, I have compression turned
> off and memmapping turned on...
mmap transfers should be able to handle fullscreen at high resolutions
without problems if you have enough CPU, memory bandwidth and use the
client with OpenGL enabled.

> If I play the videos in non-fullscreen
> mode then they play fine. It seems to me that since youtube videos
> aren't actually high dpi anyways, then there shouldn't be a difference
> between how well they play in non-fullscreen mode and how well they play
> full screen.
You would think that... except that the browser will render at the
resolution requested by the client, and we will grab the pixels and
forward them at that resolution, which can be expensive.
(there are ways to capture the video at its original unscaled size, but
this has not been implemented yet)

> Would it be technically possible for xpra to detect that it
> is being slow, and to automatically start passing a lower dpi version of
> the window contents? I don't know if that's crazy or not, as I don't
> know how xpra internals work...
This feature already exists but it isn't enabled with mmap, as it should
not be needed in this case.

Here it is from the man page:
    How  much automatic video downscaling should be used, from 1
    (rarely) to 100 (aggressively), 0 to disable. Video scaling is
    normally used with video regions or very large windows (especially
    full screen windows) to try to maintain a decent framerate.
    Video downscaling negatively affects visual quality and will
    cause automatic refreshes (if enabled), it is most useful on video
    content where it saves a considerable amount of bandwidth.


> Tim
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