Re: [Qemu-devel] Question about hardware cursor in VGA

[BALATON Zoltan]

On Wed, 6 Mar 2019, Gerd Hoffmann wrote:
> On Wed, Mar 06, 2019 at 12:48:59AM +0100, BALATON Zoltan wrote:
> > On Tue, 5 Mar 2019, Gerd Hoffmann wrote:
> > > Use dpy_cursor_define().
> >
> > I've done that but it's not working very well. The mouse pointer is quite
> > jumpy with this and there are some problems updating the pointer image when
> > the guest changes image data in video ram without changing registers. (Like
>
> When using a relative pointing device (i.e. mouse instead of tablet) you
> also need dpy_mouse_set(), to update the host mouse position when the
> guest moves the cursor sprite around.

Sure, I figured that out otherwise the mouse pointer would not move.

> Is it possible to figure where the cursor hotspot is?

Not sure what you mean. I call dpy_mouse_set() on writing the reg that 
contains mouse position. Hot spot is always top left of sprite (or I don't 
know where it's set). I'll submit a v5 after adding some more checks to 
make it a bit safer then you can have a look.

> > least doing hw cursor like this works somewhat but I note that the other
> > version with cursor_invalidate and cursor_draw_line callbacks worked much
> > smoother, alas I've found that cannot work with shared_surface.
>
> There is a VGAComminState->force_shadow ...

Yes, but that would also make things slower so I like to keep advantage of 
shared_surface and try to fix the jumpy mouse we get with define_cursor 
instead if possible.

> > should be? (Also note that draw_line callback could do complement pixels but
> > that's not possible with dpy_cursor_define.)
>
> Yep, dpy_cursor_define is designed for the way modern hardware handles
> hardware cursors, to allow it being used as hardware cursor on the host.
> cirrus has a few modes which modern hardware can't do, thats why it
> doesn't use dpy_cursor_define.
>
> Has ati cursor a complement pixel mode too?

Yes, this part dates back to first ATI VGA chips is seem and has the 2 bit 
Windows mouse encoding (fg, bg, transparent, complement) but we can 
probably live without that if it gives us faster display for a few bad 
pixels in mouse pointer.

Regards,
BALATON Zoltan