mirror of
https://github.com/gnif/LookingGlass.git
synced 2024-11-22 21:47:23 +00:00
67 lines
2.6 KiB
ReStructuredText
67 lines
2.6 KiB
ReStructuredText
|
Technical FAQ
|
||
|
|
#############
|
||
|
|
|
||
|
|
This FAQ is targetted at developers or technical people that want to
|
||
|
|
know more about what's going on under the hood.
|
||
|
|
|
||
|
|
.. _ivshmemshared_ram:
|
||
|
|
|
||
|
|
IVSHMEM/Shared RAM
|
||
|
|
------------------
|
||
|
|
|
||
|
|
.. _what_exactly_is_the_ivshmem_device:
|
||
|
|
|
||
|
|
What exactly is the IVSHMEM device?
|
||
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||
|
|
|
||
|
|
This is a virtual device that maps a segment of shared memory into the
|
||
|
|
guest via a BAR (Base Address Register). It also has additional features
|
||
|
|
such as interrupt triggering for synchronization however we do not use
|
||
|
|
these.
|
||
|
|
|
||
|
|
.. _what_is_the_ivshmem_device_being_used_for:
|
||
|
|
|
||
|
|
What is the IVSHMEM device being used for?
|
||
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||
|
|
|
||
|
|
One might assume that we are simply using the device for the captured
|
||
|
|
frames, this, however, is not entirely accurate. Looking Glass also
|
||
|
|
needs to capture mouse shape changes (the mouse cursor), and mouse
|
||
|
|
movement events and feed these back to the client to render. We need
|
||
|
|
this additional information as we actually are rendering the cursor on
|
||
|
|
the client-side, independent of the frame capture. This is why when you
|
||
|
|
move your cursor around it doesn't affect the UPS, which is only
|
||
|
|
counting frame updates.
|
||
|
|
|
||
|
|
.. _why_do_you_need_the_mouse_positional_information:
|
||
|
|
|
||
|
|
Why do you need the mouse positional information?
|
||
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||
|
|
|
||
|
|
Windows has no notion of an absolute pointing device unless you are
|
||
|
|
using a tablet, which does work, however, if you also want relative
|
||
|
|
input for applications/games that require cursor capture, you need a
|
||
|
|
relative input device such as a PS/2 mouse.
|
||
|
|
|
||
|
|
The problem is, due to the design of QEMU or the Windows mouse subsystem
|
||
|
|
(not sure which), when the VM has both devices attached (which is the
|
||
|
|
default for libvirt), mouse click events are always at the last location
|
||
|
|
of the absolute positional device (tablet) even if the cursor has been
|
||
|
|
moved with the relative input device.
|
||
|
|
|
||
|
|
Because of this bug, we need to always operate in relative mouse input
|
||
|
|
mode, and since factors like windows mouse acceleration, or cursor
|
||
|
|
movement by a user application may occur in the guest, we need to pass
|
||
|
|
this information back so the client can render the cursor in the correct
|
||
|
|
location.
|
||
|
|
|
||
|
|
.. _why_does_lg_poll_for_updates_instead_of_using_interrupts:
|
||
|
|
|
||
|
|
Why does LG poll for updates instead of using interrupts?
|
||
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||
|
|
|
||
|
|
Initially, we were using interrupts in early designs however it became
|
||
|
|
clear that the performance, especially for high update rate mice was
|
||
|
|
extremely poor. This may have improved in recent QEMU versions and
|
||
|
|
perhaps should be re-evaluated at some point.
|