[PATCH xserver] xwayland: use wayland axis_discrete event

[Peter Hutterer]

On Mon, Aug 06, 2018 at 06:09:26PM +1200, Scott Anderson wrote:
> This prevents multiple scroll events happening for wayland compositors
> which send axis values other than 10. For example, libinput will
> typically return 15 for each scroll wheel step, and if a wayland
> compositor sends those to xwayland without normalising them, 2 scroll
> wheel steps will end up as 3 xorg scroll events. By listening for the
> discrete_axis event, this will now correctly send only 2 xorg scroll
> events.
> 
> The wayland protocol gurantees that there will always be an axis event
> following an axis_discrete event. However, it does not gurantee that
> other events (including other axis_discrete+axis pairs) will not happen
> in between them. So we must keep a list of outstanding axis_discrete
> events.
> 
> Signed-off-by: Scott Anderson <scott at anderso.nz>

Reviewed-by: Peter Hutterer <peter.hutterer at who-t.net>

Cheers,
   Peter

> ---
>  hw/xwayland/xwayland-input.c | 41 +++++++++++++++++++++++++++++++++++-
>  hw/xwayland/xwayland.h       |  1 +
>  2 files changed, 41 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/xwayland/xwayland-input.c b/hw/xwayland/xwayland-input.c
> index a602f0887..6fd3c416b 100644
> --- a/hw/xwayland/xwayland-input.c
> +++ b/hw/xwayland/xwayland-input.c
> @@ -37,6 +37,12 @@
>  #include <misc.h>
>  #include "tablet-unstable-v2-client-protocol.h"
>  
> +struct axis_discrete_pending {
> +    struct xorg_list l;
> +    uint32_t axis;
> +    int32_t discrete;
> +};
> +
>  struct sync_pending {
>      struct xorg_list l;
>      DeviceIntPtr pending_dev;
> @@ -565,6 +571,8 @@ pointer_handle_axis(void *data, struct wl_pointer *pointer,
>      int index;
>      const int divisor = 10;
>      ValuatorMask mask;
> +    struct axis_discrete_pending *pending = NULL;
> +    struct axis_discrete_pending *iter;
>  
>      switch (axis) {
>      case WL_POINTER_AXIS_VERTICAL_SCROLL:
> @@ -577,8 +585,22 @@ pointer_handle_axis(void *data, struct wl_pointer *pointer,
>          return;
>      }
>  
> +    xorg_list_for_each_entry(iter, &xwl_seat->axis_discrete_pending, l) {
> +        if (iter->axis == axis) {
> +            pending = iter;
> +            break;
> +        }
> +    }
> +
>      valuator_mask_zero(&mask);
> -    valuator_mask_set_double(&mask, index, wl_fixed_to_double(value) / divisor);
> +
> +    if (pending) {
> +        valuator_mask_set(&mask, index, pending->discrete);
> +        xorg_list_del(&pending->l);
> +        free(pending);
> +    } else {
> +        valuator_mask_set_double(&mask, index, wl_fixed_to_double(value) / divisor);
> +    }
>      QueuePointerEvents(xwl_seat->pointer, MotionNotify, 0, POINTER_RELATIVE, &mask);
>  }
>  
> @@ -608,6 +630,16 @@ static void
>  pointer_handle_axis_discrete(void *data, struct wl_pointer *wl_pointer,
>                               uint32_t axis, int32_t discrete)
>  {
> +    struct xwl_seat *xwl_seat = data;
> +
> +    struct axis_discrete_pending *pending = malloc(sizeof *pending);
> +    if (!pending)
> +        return;
> +
> +    pending->axis = axis;
> +    pending->discrete = discrete;
> +
> +    xorg_list_add(&pending->l, &xwl_seat->axis_discrete_pending);
>  }
>  
>  static const struct wl_pointer_listener pointer_listener = {
> @@ -1337,6 +1369,7 @@ create_input_device(struct xwl_screen *xwl_screen, uint32_t id, uint32_t version
>      wl_array_init(&xwl_seat->keys);
>  
>      xorg_list_init(&xwl_seat->touches);
> +    xorg_list_init(&xwl_seat->axis_discrete_pending);
>      xorg_list_init(&xwl_seat->sync_pending);
>  }
>  
> @@ -1345,6 +1378,7 @@ xwl_seat_destroy(struct xwl_seat *xwl_seat)
>  {
>      struct xwl_touch *xwl_touch, *next_xwl_touch;
>      struct sync_pending *p, *npd;
> +    struct axis_discrete_pending *ad, *ad_next;
>  
>      xorg_list_for_each_entry_safe(xwl_touch, next_xwl_touch,
>                                    &xwl_seat->touches, link_touch) {
> @@ -1357,6 +1391,11 @@ xwl_seat_destroy(struct xwl_seat *xwl_seat)
>          free (p);
>      }
>  
> +    xorg_list_for_each_entry_safe(ad, ad_next, &xwl_seat->axis_discrete_pending, l) {
> +        xorg_list_del(&ad->l);
> +        free(ad);
> +    }
> +
>      release_tablet_manager_seat(xwl_seat);
>  
>      release_grab(xwl_seat);
> diff --git a/hw/xwayland/xwayland.h b/hw/xwayland/xwayland.h
> index d70ad54bf..1a6e2f380 100644
> --- a/hw/xwayland/xwayland.h
> +++ b/hw/xwayland/xwayland.h
> @@ -272,6 +272,7 @@ struct xwl_seat {
>      char *keymap;
>      struct wl_surface *keyboard_focus;
>  
> +    struct xorg_list axis_discrete_pending;
>      struct xorg_list sync_pending;
>  
>      struct xwl_pointer_warp_emulator *pointer_warp_emulator;
> -- 
> 2.18.0
> 
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