/**
* clutter_gesture_action_get_velocity:
* @action: a #ClutterGestureAction
* @point: the touch point index, with 0 being the first touch
* point received by the action
* @velocity_x: (out) (allow-none): return location for the latest motion
* event's X velocity
* @velocity_y: (out) (allow-none): return location for the latest motion
* event's Y velocity
*
* Retrieves the velocity, in stage pixels per millisecond, of the
* latest motion event during the dragging.
*
* Since: 1.12
*/
gfloat
clutter_gesture_action_get_velocity (ClutterGestureAction *action,
guint point,
gfloat *velocity_x,
gfloat *velocity_y)
{
gfloat d_x, d_y, distance, velocity;
gint64 d_t;
g_return_val_if_fail (CLUTTER_IS_GESTURE_ACTION (action), 0);
g_return_val_if_fail (action->priv->points->len > point, 0);
distance = clutter_gesture_action_get_motion_delta (action, point,
&d_x, &d_y);
d_t = g_array_index (action->priv->points,
GesturePoint,
point).last_delta_time;
if (velocity_x)
*velocity_x = d_t > FLOAT_EPSILON ? d_x / d_t : 0;
if (velocity_y)
*velocity_y = d_t > FLOAT_EPSILON ? d_y / d_t : 0;
velocity = d_t > FLOAT_EPSILON ? distance / d_t : 0;
return velocity;
}
/**
* clutter_pan_action_get_motion_delta:
* @self: A #ClutterPanAction
* @point: the touch point index, with 0 being the first touch
* point received by the action
* @delta_x: (out) (allow-none): return location for the X delta
* @delta_y: (out) (allow-none): return location for the Y delta
*
* Retrieves the delta, in stage space, dependent on the current state
* of the #ClutterPanAction. If it is inactive, both fields will be
* set to 0. If it is panning by user action, the values will be equivalent
* to those returned by clutter_gesture_action_get_motion_delta().
* If it is interpolating with some form of kinetic scrolling, the values
* will be equivalent to those returned by
* clutter_pan_action_get_interpolated_delta(). This is a convenience
* method designed to be used in replacement "pan" signal handlers.
*/
gfloat
clutter_pan_action_get_motion_delta (ClutterPanAction *self,
guint point,
gfloat *delta_x,
gfloat *delta_y)
{
ClutterPanActionPrivate *priv;
g_return_val_if_fail (CLUTTER_IS_PAN_ACTION (self), 0.0f);
priv = self->priv;
switch (priv->state)
{
case PAN_STATE_INACTIVE:
if (delta_x)
*delta_x = 0;
if (delta_y)
*delta_y = 0;
return 0;
case PAN_STATE_PANNING:
return clutter_gesture_action_get_motion_delta (CLUTTER_GESTURE_ACTION (self),
point, delta_x, delta_y);
case PAN_STATE_INTERPOLATING:
return clutter_pan_action_get_interpolated_delta (self, delta_x, delta_y);
default:
g_assert_not_reached ();
}
}
static gboolean
on_pan (ClutterPanAction *action,
ClutterActor *scroll,
gboolean is_interpolated,
gpointer *user_data)
{
gfloat delta_x, delta_y;
const ClutterEvent *event = NULL;
if (is_interpolated)
clutter_pan_action_get_interpolated_delta (action, &delta_x, &delta_y);
else
{
clutter_gesture_action_get_motion_delta (CLUTTER_GESTURE_ACTION (action), 0, &delta_x, &delta_y);
event = clutter_gesture_action_get_last_event (CLUTTER_GESTURE_ACTION (action), 0);
}
g_print ("[%s] panning dx:%.2f dy:%.2f\n",
event == NULL ? "INTERPOLATED" :
event->type == CLUTTER_MOTION ? "MOTION" :
event->type == CLUTTER_TOUCH_UPDATE ? "TOUCH UPDATE" :
"?",
delta_x, delta_y);
return TRUE;
}
static void
gesture_end (ClutterGestureAction *gesture,
ClutterActor *actor)
{
ClutterPanAction *self = CLUTTER_PAN_ACTION (gesture);
ClutterPanActionPrivate *priv = self->priv;
gfloat velocity, velocity_x, velocity_y;
gfloat delta_x, delta_y;
gfloat tau;
gint duration;
clutter_gesture_action_get_release_coords (CLUTTER_GESTURE_ACTION (self), 0, &priv->release_x, &priv->release_y);
if (!priv->should_interpolate)
{
priv->state = PAN_STATE_INACTIVE;
return;
}
priv->state = PAN_STATE_INTERPOLATING;
clutter_gesture_action_get_motion_delta (gesture, 0, &delta_x, &delta_y);
velocity = clutter_gesture_action_get_velocity (gesture, 0, &velocity_x, &velocity_y);
/* Exponential timing constant v(t) = v(0) * exp(-t/tau)
* tau = 1000ms / (frame_per_second * - ln(decay_per_frame))
* with frame_per_second = 60 and decay_per_frame = 0.95, tau ~= 325ms
* see http://ariya.ofilabs.com/2011/10/flick-list-with-its-momentum-scrolling-and-deceleration.html */
tau = 1000.0f / (reference_fps * - logf (priv->deceleration_rate));
/* See where the decreasing velocity reaches $min_velocity px/ms
* v(t) = v(0) * exp(-t/tau) = min_velocity
* t = - tau * ln( min_velocity / |v(0)|) */
duration = - tau * logf (min_velocity / (ABS (velocity) * priv->acceleration_factor));
/* Target point: x(t) = v(0) * tau * [1 - exp(-t/tau)] */
priv->target_x = velocity_x * priv->acceleration_factor * tau * (1 - exp ((float)-duration / tau));
priv->target_y = velocity_y * priv->acceleration_factor * tau * (1 - exp ((float)-duration / tau));
if (ABS (velocity) * priv->acceleration_factor > min_velocity && duration > FLOAT_EPSILON)
{
priv->interpolated_x = priv->interpolated_y = 0.0f;
priv->deceleration_timeline = clutter_timeline_new (duration);
clutter_timeline_set_progress_mode (priv->deceleration_timeline, CLUTTER_EASE_OUT_EXPO);
g_signal_connect (priv->deceleration_timeline, "new_frame",
G_CALLBACK (on_deceleration_new_frame), self);
g_signal_connect (priv->deceleration_timeline, "stopped",
G_CALLBACK (on_deceleration_stopped), self);
clutter_timeline_start (priv->deceleration_timeline);
}
else
{
emit_pan_stopped (self, actor);
}
}
