[PATCH libinput 1/2] Change the scroll step distance to 15 and document it as degrees

[Jonas Ådahl]

On Mon, Jan 12, 2015 at 09:12:35AM +1000, Peter Hutterer wrote:
> Similar to the mouse resolution, let's make the scroll distance a sensible
> predictable value. Most mice use a 15 degree angle per scroll click, so let's
> change to that. This will alter behaviour in clients that expect 10 but it
> shouldn't be too bad. We return doubles anyway for the axis value, so that
> leaves the option of really fine-grained step sizes.

This is not entirely true, as a few clients use the '10' value to
convert to steps. In other words this change may cause them to
potentially emit double scroll events. We need to make weston (and other
users) not break compatibility with Wayland clients by, as discussed, for
now ignoring the degrees and continue sending the distance based value
for wheel events.

Other than this, one nit below, and with that fixed,

Reviewed-by: Jonas Ådahl <jadahl at gmail.com>


Jonas

> 
> We currently assume all mice have 15 degree angles. Like the DPI settings, it
> will require a udev property to be set. Patch for that to follow.
> 
> Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>
> ---
>  src/evdev.c    | 2 +-
>  src/libinput.h | 8 ++++----
>  test/pointer.c | 4 ++--
>  3 files changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/src/evdev.c b/src/evdev.c
> index 1718491..4fb37d6 100644
> --- a/src/evdev.c
> +++ b/src/evdev.c
> @@ -40,7 +40,7 @@
>  #include "filter.h"
>  #include "libinput-private.h"
>  
> -#define DEFAULT_AXIS_STEP_DISTANCE 10
> +#define DEFAULT_AXIS_STEP_DISTANCE 15

This is no longer a distance, as the value is changed from distance to
angle.

>  #define DEFAULT_MIDDLE_BUTTON_SCROLL_TIMEOUT 200
>  
>  enum evdev_key_type {
> diff --git a/src/libinput.h b/src/libinput.h
> index 27c5868..95a5c1d 100644
> --- a/src/libinput.h
> +++ b/src/libinput.h
> @@ -704,10 +704,10 @@ libinput_event_pointer_get_axis_value(struct libinput_event_pointer *event);
>   *
>   * If the source is @ref LIBINPUT_POINTER_AXIS_SOURCE_WHEEL, no terminating
>   * event is guaranteed (though it may happen).
> - * Scrolling is in discrete steps, a value of 10 representing one click
> - * of a typical mouse wheel. Some mice may have differently grained wheels,
> - * libinput will adjust the value accordingly. It is up to the caller how to
> - * interpret such different step sizes.
> + * Scrolling is in discrete steps, the value is the angle the wheel moved
> + * in degrees. The default is 15 degrees per wheel click, but some mice may
> + * have differently grained wheels. It is up to the caller how to interpret
> + * such different step sizes.
>   *
>   * If the source is @ref LIBINPUT_POINTER_AXIS_SOURCE_CONTINUOUS, no
>   * terminating event is guaranteed (though it may happen).
> diff --git a/test/pointer.c b/test/pointer.c
> index b9bd3cc..d12c9f6 100644
> --- a/test/pointer.c
> +++ b/test/pointer.c
> @@ -350,8 +350,8 @@ test_wheel_event(struct litest_device *dev, int which, int amount)
>  	struct libinput_event_pointer *ptrev;
>  
>  	/* the current evdev implementation scales the scroll wheel events
> -	   up by a factor 10 */



> -	const int scroll_step = 10;
> +	   up by a factor 15 */
> +	const int scroll_step = 15;
>  	int expected = amount * scroll_step;
>  
>  	if (libinput_device_config_scroll_get_natural_scroll_enabled(dev->libinput_device))
> -- 
> 2.1.0
> 
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