Re: [PATCH 3/3] ui/cocoa: Adds support for mouse cursors

[Akihiko Odaki <akihiko.odaki@daynix.com>]

On 2024/06/09 5:20, Phil Dennis-Jordan wrote:
> This change implements the callbacks dpy_cursor_define and dpy_mouse_set
> for the Cocoa UI. The incoming mouse cursor image is converted into an
> NSCursor object, allowing the guest mouse cursor to be rendered as the
> host's native OS cursor on macOS.
> 
> This is straightforward in absolute pointing mode, but rather trickier
> with a relative pointing device:
> 
>   1. The cursor position in Qemu's coordinate system must be translated
>      and converted into macOS's Core Graphics/Quartz coordinates when
>      positioning the cursor. Additionally, the position already includes
>      the hotspot offset; we'd prefer to use the host OS's hotspot support
>      so we need subtract the hotspot vector off again.
>   2. Setting the cursor position programmatically on macOS biases the
>      next mouse movement event by the amount the cursor was shifted.
>      If we didn't reverse that bias when forwarding the next event
>      back into Qemu's input stack, this would create a feedback loop.
>      (The behaviour of affecting mouse events makes sense for e.g.
>      setting the cursor position in a remote access system.)
> 
> This change slightly improves the user experience when using virtual
> display adapter implementations which check for UI back-end cursor
> support, and fixes the issue of no visible mouse cursor when using one
> which does not. (Such as virtio-vga)

Thanks for working on ui/cocoa, but I already have submitted a patch for 
this particular problem:
https://patchew.org/QEMU/20240318-cursor-v1-0-0bbe6c382217@daynix.com/

The difference between these patches is that my patch does not use 
warping at all. I thought reversing the mouse movement bias is a fragile 
approach that depends on the details of how Quartz works.