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

["Thomas Hellström (VMware)" <thomas_os@shipmail.org>]

On 3/20/20 12:47 PM, Thomas Hellström (VMware) wrote:
> On 3/20/20 12:27 PM, Simon Ser wrote:
>> On Friday, March 20, 2020 11:59 AM, Thomas Hellström 
>> <thomas_os@shipmail.org> wrote:
>>
>>> On 3/20/20 10:13 AM, Pekka Paalanen wrote:
>>>
>>>>> It seems people are also forgetting the problem of associating the
>>>>> cursor plane with an input device, so that whatever is looking to
>>>>> mangle the cursor plane behind the KMS app's back would know how 
>>>>> to do
>>>>> it right.
>>>>> My first thought for that is a new cursor plane property with the 
>>>>> value
>>>>> of major, minor of the kernel input device that userspace is using to
>>>>> control the cursor plane. This property should be set by userspace 
>>>>> only
>>>>> when there is exactly one kernel input device it uses for controlling
>>>>> the cursor plane. Setting this property to none/disabled would be a
>>>>> clear indication that "seamless mode" would be unwanted. The DRM
>>>>> driver or whatever it talks to could then check if the cursor 
>>>>> plane is
>>>>> indeed controlled by the input it so far has only assumed and
>>>>> automatically choose correctly between seamless mode or not.
>>>> Are you sure this i really needed? VMware's SVGA device checks whether
>>>> the guest cursor position and host cursor position are reasonably
>>>> aligned, and if not, composites the guest cursor over the display 
>>>> plane.
>>>> So if you, for example,  attach a passthrough USB mouse to the VM 
>>>> while
>>>> running in seamless mode, things "just work". Similarly if you were to
>>>> attach a kms-based vnc solution that behaved in the same way and that
>>>> created a new input device, things would also look fine, except for
>>>> temporary cursor jumps when you switch input device.
>>> Seems more like a workaround than a real solution.
>
> That may be the case, but still it works and if you have multiple 
> clients it always allows the active client run in seamless mode. 
> Besides, if people think supporting KMS hotspots is already hard 
> enough, the chance of having them supplying the correct input device 
> is small.
>
> /Thomas

To be clear about this, I'm not *against* a property associating a 
device with a cursor plane as long as it's just a hint. However in the 
VMware case, it's unlikely that we will try to implement any kernel 
driver support for it since we have a working solution and it also may 
not be possible. (Some remoting solutions only work when seamless mode 
is enabled).

/Thomas


>
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