Re: Atomic KMS API lacks the ability to set cursor hot-spot coordinates

From: Pekka Paalanen <ppaalanen@gmail.com>
To: Hans de Goede <hdegoede@redhat.com>
Cc: "Michel Dänzer" <michel@daenzer.net>,
	"Jonas Ådahl" <jadahl@redhat.com>,
	"dri-devel@lists.freedesktop.org"
	<dri-devel@lists.freedesktop.org>
Subject: Re: Atomic KMS API lacks the ability to set cursor hot-spot coordinates
Date: Thu, 19 Mar 2020 14:54:40 +0200	[thread overview]
Message-ID: <20200319145440.51773af8@eldfell.localdomain> (raw)
In-Reply-To: <8db6e079-c88a-6b11-b77b-337059a139ba@redhat.com>

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On Thu, 19 Mar 2020 12:52:14 +0100
Hans de Goede <hdegoede@redhat.com> wrote:

> Hi,
> 
> On 3/19/20 12:35 PM, Michel Dänzer wrote:
> > On 2020-03-18 4:22 p.m., Simon Ser wrote:  
> >>>
> >>> On 3/18/20 3:38 PM, Simon Ser wrote:  
> >>>>  
> >>>>> 1) Letting the VM-viewer window-system draw the cursor as it normally
> >>>>> would draw it.  
> >>>>
> >>>> Why is this important? Can't the VM viewer hide the cursor and use a
> >>>> sub-surface to manually draw the cursor plane configured by the guest?  
> >>>
> >>> Because then moving the cursor as seen by the user requires a round trip
> >>> through the VM and that adds latency, esp. when the VM viewer is viewing
> >>> a VM which is running somewhere else over the network.  
> >>
> >> The video output has latency anyway.  
> > 
> > Sounds like you've never tried the two different modes yourself? :) IME
> > it makes a big difference even with a local VM. Even very little latency
> > can make the cursor feel awkward, like it's being held back by a rubber
> > band or something.  
> 
> Right not to mention that the latency may be variable, so the cursor
> moves in a jittery fashion instead of having it move smoothly
> matching the smooth way a user normally moves the mouse.
> 
> This totally wrecks hand-eye coordination and is just plain awefull.

I have experienced it, and while it is painful, I prefer that pain over
the pain of accidentally clicking something that was not transmitted to
the remote display yet.

Therefore I think the best user experience is to use both types of
cursor at the same time: the remote desktop or VM viewer paints the
local cursor as an aid, like a phantom, and the cursor from inside the
VM is also visible with the latency it naturally has. That means I
could actually see that the screen has caught up with my motions before
I click something.

Thanks,
pq

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