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kinetic-scroll-view: Various fixes for the motion buffer #98

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kinetic-scroll-view: Various fixes for the motion buffer #98

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Commits on Sep 22, 2015

  1. kinetic-scroll-view: Handle ClutterTimeline:stopped not :completed 

    The former is always emitted when the timeline stops (either due to
reaching its duration, or due to clutter_timeline_stop() being called);
the latter is only emitted in the first case.

Changing signals means we can eliminate manual cleanup code after calls
to clutter_timeline_stop().

clutter-project#98
    Philip Withnall committed Sep 22, 2015
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  2. kinetic-scroll-view: Grow the motion buffer over time 

    The motion buffer contains a history of motion events for the current
scrolling action, starting from the initial touch event. This is used at
the release of the scroll to work out an average origin coordinate,
which is then used in the calculation of whether to use kinetic
scrolling.

Previously, the oldest entry in the motion buffer was removed if the
buffer filled up, then the buffer was expanded in size. This meant that
for scrolling actions with many motion events, the average taken over
the events would quickly creep towards the location of the most recent
motion event. This meant that, often, the threshold for starting a
kinetic scroll was not reached, and hence kinetic scrolling would not
happen.

Stop removing the oldest entry from the buffer, and instead grow it
indefinitely. This does make the widget prone to consuming all the
system’s memory if the user scrolls around for a _very_ long time. This
may be better fixed by calculating a moving average instead, and
eliminating the motion buffer.

clutter-project#98
    Philip Withnall committed Sep 22, 2015
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  3. kinetic-scroll-view: Add more debug output 

    clutter-project#98
    Philip Withnall committed Sep 22, 2015
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  4. kinetic-scroll-view: Replace motion buffer with a moving average 

    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
    Philip Withnall committed Sep 22, 2015
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  5. kinetic-scroll-view: Use gint64 for timestamps rather than GTimeVal 

    GTimeVal is a pain to use and the use of glong means the potential
for overflow when summing several timestamps on 32-bit platforms is
quite high. Instead, use gint64 and g_get_real_time().

clutter-project#98
    Philip Withnall committed Sep 22, 2015
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  6. kinetic-scroll-view: Include timestamps in debug messages 

    This makes debugging problems in the MxKineticScrollView a lot easier.
Note that _KINETIC_DEBUG must be defined to enable debug messages.

clutter-project#98
    Philip Withnall committed Sep 22, 2015
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