The way to use system cursor and custom(client) cursor

[Elvis Lee(이광웅)]

> -----Original Message-----
> From: wayland-devel-bounces+kwangwoong.lee=lge.com at lists.freedesktop.org
> [mailto:wayland-devel-bounces+kwangwoong.lee=lge.com at lists.freedesktop.org]
> On Behalf Of Pekka Paalanen
> Sent: Sunday, June 09, 2013 11:03 PM
> To: Elvis Lee (______)
> Cc: wayland-devel at lists.freedesktop.org
> Subject: Re: The way to use system cursor and custom(client) cursor
> 
> On Sun, 9 Jun 2013 16:01:48 -0700
> Elvis Lee(______) <kwangwoong.lee at lge.com> wrote:
> 
> > Hello.
> >
> >
> >
> > I feel unnatural to implement custom cursor scenario. Here is a question.
> >
> > How does a client request compositor to use system cursor?
> >
> >
> >
> > The system cursor means a current default cursor for compositor.
> >
> > Currently, client should know about the system cursor in order to use
> > it as parameter of wl_pointer.set_cursor.
> >
> > Otherwise, cursor surface should be destroyed to request compositor a
> > rollback to system cursor from custom cursor.
> >
> >
> >
> > I think it¡¯s enough to detach buffer from cursor surface for hiding
> > the cursor.
> >
> > And set_cursor(null surface) can be used to request to stop using
> > custom cursor. (rollback)
> >
> >
> >
> > Here are some states and protocols.
> >
> >
> >
> > 1.     System cursor -> Custom cursor
> >
> > A.     set_cursor(cursor_surface)
> >
> > B.      cursor_surface.attach(buffer for custom image)
> >
> > C.      cursor_surface.damage
> >
> > D.     cursor_surface.commit
> >
> >
> >
> > 2.     Custom cursor -> System cursor
> >
> > A.     set_cursor(null surface)
> >
> >
> >
> > 3.     Custom cursor -> Hide Cursor
> >
> > A.     set_cursor(cursor_surface)   (can be omitted if it is already set)
> >
> > B.      cursor_surface.attach(null buffer)
> >
> > C.      cursor_surface.commit
> >
> >
> >
> > 4.     System cursor -> Hide Cursor
> >
> > A.     set_cursor(cursor_surface)
> >
> > B.      cursor_surface.attach(null buffer) (can be omitted if it is
> already
> > detached)
> >
> > C.      cursor_surface.commit
> >
> >
> >
> > I think this can cover up a scenario when pointer enters into a
> > surface of client.
> >
> > If there is no specific cursor for client to want when pointer enters,
> > it¡¯s enough to request set_cursor(null).
> >
> >
> >
> > Is this approach possible? I want to listen your opinions.
> 
> Hi Elvis,
> 
> do I understand right, that you would like to add the concept of a system
> cursor?
> 
> I guess it would be possible, but why?
> 
> It seems the system cursor you propose would be one arbitrary cursor
> without any meaning. When and why would applications ever want to use it?
> 
> The compositor usually cannot, and there is no need to, switch to a system
> cursor on its own, so it would always be requested by a client.
> I can understand applications wanting a specific cursor, or no cursor, but
> what would be the purpose of a system cursor?
> 
> If you also consider cursor themes, the system cursor would be from one
> theme. An application using a system cursor would need to use the same
> theme for its other cursors to look consistent.
> 
> We already have libwayland-cursor to help you load a cursor theme, so
> using a proper cursor should not be too hard.
> 

Hi, Pekka.

Thanks for your opinion.

Possibly, The word 'system cursor' can attract over attention.
As you said, it's just one of the cursor themes.


It might be unclear for my explain. Here is a simple scenario.
Compositor can own its cursor without client or with minimized client or outside focused client window.
And the cursor is configurable.
Compositor stared with blue cursor, then user changes it to red one.
After launching a client, the client override the cursor with specific one.
After a while, client want to use the cursor which is used by compositor just before.

There are my questions.
Which cursor should client choose? How to know about it? Or should client know about it?

For consistency whole system UX, client can use the same cursor with compositor.
As I mentioned, the cursor is configurable.
Unless we support a kind of get_cursor, client cannot know about which theme is used for the compositor.

I think client needs a way to inform that it doesn’t want to use specific cursor anymore.
It can be done with set_cursor(null).
In my case, I want to regard it as a delegation for cursor from client to compositor.
And the way to hide cursor can be replaced with detaching buffer.
That's what I want to say.

I hope that I explained well about my needs and approach.
And I think my needs might be general one.

Once again, I appreciate your attention.

Thanks.
Elvis.