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

[Phil Dennis-Jordan <phil@philjordan.eu>]

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On Sun, 9 Jun 2024 at 11:06, Akihiko Odaki <akihiko.odaki@daynix.com> wrote:

> 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/
>

Sorry, I missed this patch set - thanks for bringing it to my attention.


> 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.
>

Hmm. So, I agree that the relative cursor implementation with NSCursor is
somewhat awkward. I'm not sure it's as fragile as you make out as the
behaviour of the APIs used hasn't changed in decades and has plenty of
existing software depending on it. Still, it might behave awkwardly in the
context of other apps warping the cursor at the same time. I also
definitely think host cursor integration is useful and valuable, at least
in absolute pointing mode - for example, when the host system is itself
being remote controlled, and also to avoid the cursor being cropped near
the edges of the guest viewport.

The CALayer based rendering makes sense to me in relative mode though. For
one, it avoids the complicated event offsets. The cursor cropping actually
makes sense as a visual cue when the cursor is actually constrained to the
guest viewport while mouse input is grabbed. And because the guest cursor
is decoupled from the host cursor even after ungrabbing, it makes sense to
continue rendering it even when Qemu has relinquished the host cursor.

I've therefore reworked my NSCursor code on top of your CALayer cursor and
change notifier work so that the NSCursor is visible and updated with the
guest's cursor image when in absolute mode, and the CALayer draws the
cursor in relative mode. Because of the chain of patch dependencies I've
staged it on gitlab here for initial feedback/testing/review:
https://gitlab.com/pmdj/qemu-upstreaming/-/compare/master...m-cocoa-cursors-2.0?from_project_id=53960510&straight=false

Let me know what you think. If we decide to go with this approach we can
post our respective patches as a combined v2 patchset to the list.

Incidentally, that version of my NSCursor patch includes a few
refinements/fixes to the CALayer patch which I'll tease out into a separate
commit, and which I'd recommend applying even if consensus settles on a
CALayer-only approach. (setCursor: was rather long and messy; it also
leaked a colour space object; layer and cursor objects would leak if the
view was hypothetically dealloc'd)

Thanks,
Phil

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