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kinetic-scroll-view: Replace motion buffer with a moving average
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The motion buffer stored each motion event which happened in a sequence
(for example, a single swipe) on the kinetic scroll view, in order that
the average event coordinates and time could be computed at the end of
the sequence (on releasing the touchscreen). This could lead to problems
with very long event sequences — potentially allocating a huge event
array and leading to allocation failure.

Avoid that by computing the average of the events as they are received.

clutter-project#98
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Philip Withnall committed Sep 21, 2015
1 parent a54afe0 commit 41a820c
Showing 1 changed file with 102 additions and 110 deletions.
212 changes: 102 additions & 110 deletions mx/mx-kinetic-scroll-view.c
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Original file line number Diff line number Diff line change
Expand Up @@ -44,6 +44,7 @@
#include "mx-scrollable.h"
#include "mx-focusable.h"
#include <math.h>
#include <string.h>

#define _KINETIC_DEBUG 0

Expand Down Expand Up @@ -98,9 +99,21 @@ struct _MxKineticScrollViewPrivate

MxAutomaticScroll in_automatic_scroll;

/* Mouse motion event information */
GArray *motion_buffer;
guint last_motion;
/* Mouse motion event information.
* @motion_origin is the details of the first motion event in a sequence.
* @motion_last is the most recent motion event in a sequence.
* @motion_total is the total value of all the motion events in a sequence.
* FIXME: The code does not currently handle overflow here.
* @n_motions is the number of events used in the calculation of
* @motion_total.
*
* @motion_origin, @motion_last and @motion_total are valid iff
* @n_motions > 0.
*/
MxKineticScrollViewMotion motion_origin;
MxKineticScrollViewMotion motion_last;
MxKineticScrollViewMotion motion_total;
guint n_motions;

/* Variables for storing acceleration information */
ClutterTimeline *deceleration_timeline;
Expand Down Expand Up @@ -310,12 +323,6 @@ mx_kinetic_scroll_view_get_property (GObject *object,
g_value_set_double (value, priv->decel_rate);
break;

/*
case PROP_BUFFER_SIZE :
g_value_set_uint (value, priv->motion_buffer->len);
break;
*/

case PROP_HADJUST:
mx_kinetic_scroll_view_get_adjustments (MX_SCROLLABLE (object),
&adjustment, NULL);
Expand Down Expand Up @@ -483,16 +490,6 @@ mx_kinetic_scroll_view_dispose (GObject *object)
G_OBJECT_CLASS (mx_kinetic_scroll_view_parent_class)->dispose (object);
}

static void
mx_kinetic_scroll_view_finalize (GObject *object)
{
MxKineticScrollViewPrivate *priv = MX_KINETIC_SCROLL_VIEW (object)->priv;

g_array_free (priv->motion_buffer, TRUE);

G_OBJECT_CLASS (mx_kinetic_scroll_view_parent_class)->finalize (object);
}

static void
mx_kinetic_scroll_view_get_preferred_width (ClutterActor *actor,
gfloat for_height,
Expand Down Expand Up @@ -622,7 +619,6 @@ mx_kinetic_scroll_view_class_init (MxKineticScrollViewClass *klass)
object_class->get_property = mx_kinetic_scroll_view_get_property;
object_class->set_property = mx_kinetic_scroll_view_set_property;
object_class->dispose = mx_kinetic_scroll_view_dispose;
object_class->finalize = mx_kinetic_scroll_view_finalize;

actor_class->get_preferred_width = mx_kinetic_scroll_view_get_preferred_width;
actor_class->get_preferred_height = mx_kinetic_scroll_view_get_preferred_height;
Expand Down Expand Up @@ -755,6 +751,61 @@ set_state (MxKineticScrollView *scroll, MxKineticScrollViewState state)
LOG_DEBUG (scroll, "%s: finished setting state to %u", G_STRFUNC, state);
}

/* Add a motion event to the rolling average of motion events. */
static void
add_motion_event (MxKineticScrollView *scroll,
gfloat x,
gfloat y)
{
MxKineticScrollViewPrivate *priv = scroll->priv;
GTimeVal tv;

LOG_DEBUG (scroll, "%s: x = %f, y = %f, n_motions = %u",
G_STRFUNC, x, y, priv->n_motions);

g_get_current_time (&tv);

if (priv->n_motions == 0)
{
priv->motion_origin.x = x;
priv->motion_origin.y = y;
priv->motion_origin.time = tv;

memcpy (&priv->motion_last, &priv->motion_origin,
sizeof (priv->motion_last));
memcpy (&priv->motion_total, &priv->motion_origin,
sizeof (priv->motion_total));

priv->n_motions = 1;
}
else if (priv->n_motions < G_MAXUINT)
{
priv->motion_last.x = x;
priv->motion_last.y = y;
priv->motion_last.time = tv;

priv->motion_total.x += x;
priv->motion_total.y += y;
priv->motion_total.time.tv_sec += tv.tv_sec;
priv->motion_total.time.tv_usec += tv.tv_usec;

/* Avoid overflow by only taking this branch if n_motions will not
* overflow. Subsequent motions are ignored. */
priv->n_motions++;
}
}

static void
reset_motion_events (MxKineticScrollView *scroll)
{
MxKineticScrollViewPrivate *priv = scroll->priv;

memset (&priv->motion_origin, 0, sizeof (priv->motion_origin));
memset (&priv->motion_last, 0, sizeof (priv->motion_last));
memset (&priv->motion_total, 0, sizeof (priv->motion_total));
priv->n_motions = 0;
}

static gboolean
motion_event_cb (ClutterActor *actor,
ClutterEvent *event,
Expand Down Expand Up @@ -837,9 +888,8 @@ motion_event_cb (ClutterActor *actor,

g_object_get (G_OBJECT (settings),
"drag-threshold", &threshold, NULL);
g_assert (priv->motion_buffer->len > 0);
motion = &g_array_index (priv->motion_buffer,
MxKineticScrollViewMotion, 0);
g_assert (priv->n_motions > 0);
motion = &priv->motion_origin;

dx = ABS (motion->x - x);
dy = ABS (motion->y - y);
Expand Down Expand Up @@ -921,10 +971,10 @@ motion_event_cb (ClutterActor *actor,
return FALSE;
}

g_assert (priv->motion_buffer->len > 0);
g_assert (priv->n_motions > 0);
LOG_DEBUG (scroll, "motion dx=%f dy=%f",
ABS (g_array_index (priv->motion_buffer, MxKineticScrollViewMotion, priv->motion_buffer->len - 1).x - x),
ABS (g_array_index (priv->motion_buffer, MxKineticScrollViewMotion, priv->motion_buffer->len - 1).y - y));
ABS (priv->motion_last.x - x),
ABS (priv->motion_last.y - y));

if (priv->child)
{
Expand All @@ -934,10 +984,7 @@ motion_event_cb (ClutterActor *actor,
mx_scrollable_get_adjustments (MX_SCROLLABLE (priv->child),
&hadjust, &vadjust);

g_assert (priv->last_motion < priv->motion_buffer->len);
motion = &g_array_index (priv->motion_buffer,
MxKineticScrollViewMotion,
priv->last_motion);
motion = &priv->motion_last;

if (!priv->align_tested)
{
Expand Down Expand Up @@ -979,18 +1026,7 @@ motion_event_cb (ClutterActor *actor,
}
}

priv->last_motion ++;
if (priv->last_motion == priv->motion_buffer->len)
{
LOG_DEBUG (scroll, "increase buffer size to %u", priv->last_motion);
g_array_set_size (priv->motion_buffer, priv->last_motion + 1);
}

motion = &g_array_index (priv->motion_buffer,
MxKineticScrollViewMotion, priv->last_motion);
motion->x = x;
motion->y = y;
g_get_current_time (&motion->time);
add_motion_event (scroll, x, y);
}

return swallow;
Expand Down Expand Up @@ -1306,7 +1342,8 @@ release_event (MxKineticScrollView *scroll,

priv->device = NULL;
priv->sequence = NULL;
priv->last_motion = 0;
reset_motion_events (scroll);

return FALSE;
}

Expand All @@ -1326,40 +1363,24 @@ release_event (MxKineticScrollView *scroll,
MxAdjustment *hadjust, *vadjust;
glong time_diff;
guint duration;
gint i;

/* Get time delta */
g_get_current_time (&release_time);

/* Get average position/time of last x mouse events */
priv->last_motion ++;
if (priv->last_motion == priv->motion_buffer->len)
{
LOG_DEBUG (scroll, "increase buffer size to %u",
priv->last_motion);
g_array_set_size (priv->motion_buffer, priv->last_motion + 1);
}

x_origin = y_origin = 0;
motion_time = (GTimeVal){ 0, 0 };
for (i = 0; i < priv->last_motion; i++)
{
MxKineticScrollViewMotion *motion =
&g_array_index (priv->motion_buffer, MxKineticScrollViewMotion, i);

/* FIXME: This doesn't guard against overflows - Should
* either fix that, or calculate the correct maximum
* value for the buffer size
*/
x_origin += motion->x;
y_origin += motion->y;
motion_time.tv_sec += motion->time.tv_sec;
motion_time.tv_usec += motion->time.tv_usec;
}
x_origin = x_origin / priv->last_motion;
y_origin = y_origin / priv->last_motion;
motion_time.tv_sec /= priv->last_motion;
motion_time.tv_usec /= priv->last_motion;
g_assert (priv->n_motions > 0);

x_origin = priv->motion_total.x / priv->n_motions;
y_origin = priv->motion_total.y / priv->n_motions;
motion_time.tv_sec = priv->motion_total.time.tv_sec / priv->n_motions;
motion_time.tv_usec = priv->motion_total.time.tv_usec / priv->n_motions;

/* Normalise the GTimeVal. */
motion_time.tv_sec += motion_time.tv_usec / G_USEC_PER_SEC;
motion_time.tv_usec %= G_USEC_PER_SEC;

if (motion_time.tv_sec == release_time.tv_sec)
time_diff = release_time.tv_usec - motion_time.tv_usec;
Expand Down Expand Up @@ -1401,13 +1422,13 @@ release_event (MxKineticScrollView *scroll,
"event_x = %f, event_y = %f, y = %f, nx = %f, ny = %f, "
"n = %f, frac = %f, x_origin = %f, y_origin = %f, "
"time_diff = %lu, duration = %u, "
"priv->last_motion = %u, priv->dx = %f, "
"priv->n_motions = %u, priv->dx = %f, "
"priv->dy = %f, priv->decel_rate = %f, "
"priv->overshoot = %f, priv->accumulated_delta = %f, "
"priv->acceleration_factor = %f",
G_STRFUNC, x_pos, y_pos, event_x, event_y,
y, nx, ny, n, frac, x_origin, y_origin, time_diff,
duration, priv->last_motion, priv->dx, priv->dy,
duration, priv->n_motions, priv->dx, priv->dy,
priv->decel_rate, priv->overshoot,
priv->accumulated_delta, priv->acceleration_factor);

Expand Down Expand Up @@ -1518,14 +1539,14 @@ release_event (MxKineticScrollView *scroll,
"d = %f, ax = %f, ay = %f, y = %f, nx = %f, ny = %f, "
"n = %f, frac = %f, x_origin = %f, y_origin = %f, "
"time_diff = %lu, duration = %u, "
"priv->last_motion = %u, priv->dx = %f, "
"priv->n_motions = %u, priv->dx = %f, "
"priv->dy = %f, priv->decel_rate = %f, "
"priv->overshoot = %f, priv->accumulated_delta = %f, "
"priv->acceleration_factor = %f",
G_STRFUNC, x_pos, y_pos, event_x, event_y, value,
lower, upper, step_increment, page_size, d, ax, ay, y,
nx, ny, n, frac, x_origin, y_origin, time_diff,
duration, priv->last_motion, priv->dx, priv->dy,
duration, priv->n_motions, priv->dx, priv->dy,
priv->decel_rate, priv->overshoot,
priv->accumulated_delta, priv->acceleration_factor);

Expand Down Expand Up @@ -1566,7 +1587,7 @@ release_event (MxKineticScrollView *scroll,
priv->device = NULL;

/* Reset motion event buffer */
priv->last_motion = 0;
reset_motion_events (scroll);

if (!decelerating)
clamp_adjustments (scroll, priv->clamp_duration, TRUE, TRUE);
Expand All @@ -1582,27 +1603,27 @@ press_event (MxKineticScrollView *scroll,
MxKineticScrollViewPrivate *priv = scroll->priv;
ClutterActor *actor = (ClutterActor *) scroll;
ClutterActor *stage = clutter_actor_get_stage (actor);
MxKineticScrollViewMotion *motion;
gfloat event_x, event_y;

/* Reset automatic-scroll setting */
priv->in_automatic_scroll = MX_AUTOMATIC_SCROLL_NONE;
priv->align_tested = 0;

/* Reset motion buffer */
priv->last_motion = 0;
motion = &g_array_index (priv->motion_buffer, MxKineticScrollViewMotion, 0);
motion->x = x;
motion->y = y;
reset_motion_events (scroll);

event_x = x;
event_y = y;

LOG_DEBUG (scroll, "initial point(%fx%f)", x, y);

if (clutter_actor_transform_stage_point (actor, x, y,
&motion->x, &motion->y))
&event_x, &event_y))
{
guint threshold;
MxSettings *settings = mx_settings_get_default ();

g_get_current_time (&motion->time);
add_motion_event (scroll, event_x, event_y);

if (priv->deceleration_timeline)
{
Expand Down Expand Up @@ -1815,9 +1836,6 @@ mx_kinetic_scroll_view_init (MxKineticScrollView *self)
MxKineticScrollViewPrivate *priv = self->priv =
KINETIC_SCROLL_VIEW_PRIVATE (self);

priv->motion_buffer =
g_array_sized_new (FALSE, TRUE, sizeof (MxKineticScrollViewMotion), 30);
g_array_set_size (priv->motion_buffer, 3);
priv->decel_rate = 1.1f;
priv->button = 1;
priv->scroll_policy = MX_SCROLL_POLICY_BOTH;
Expand Down Expand Up @@ -1925,32 +1943,6 @@ mx_kinetic_scroll_view_get_deceleration (MxKineticScrollView *scroll)
return scroll->priv->decel_rate;
}

/*
void
mx_kinetic_scroll_view_set_buffer_size (MxKineticScrollView *scroll,
guint size)
{
MxKineticScrollViewPrivate *priv;
g_return_if_fail (MX_IS_KINETIC_SCROLL_VIEW (scroll));
g_return_if_fail (size > 0);
priv = scroll->priv;
if (priv->motion_buffer->len != size)
{
g_array_set_size (priv->motion_buffer, size);
g_object_notify (G_OBJECT (scroll), "buffer-size");
}
}
guint
mx_kinetic_scroll_view_get_buffer_size (MxKineticScrollView *scroll)
{
g_return_val_if_fail (MX_IS_KINETIC_SCROLL_VIEW (scroll), 0);
return scroll->priv->motion_buffer->len;
}
*/

/**
* mx_kinetic_scroll_view_set_mouse_button:
* @scroll: A #MxKineticScrollView
Expand Down

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