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/*
* Copyright (C) 2016 Igalia S.L.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
* THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "config.h"
#include "ScrollAnimationKinetic.h"
#include "ScrollableArea.h"
#include <wtf/CurrentTime.h>
/*
* PerAxisData is a port of GtkKineticScrolling as of GTK+ 3.20,
* mimicking its API and its behavior.
*
* All our curves are second degree linear differential equations, and
* so they can always be written as linear combinations of 2 base
* solutions. coef1 and coef2 are the coefficients to these two base
* solutions, and are computed from the initial position and velocity.
*
* In the case of simple deceleration, the differential equation is
*
* y'' = -my'
*
* With m the resistence factor. For this we use the following 2
* base solutions:
*
* f1(x) = 1
* f2(x) = exp(-mx)
*
* In the case of overshoot, the differential equation is
*
* y'' = -my' - ky
*
* With m the resistance, and k the spring stiffness constant. We let
* k = m^2 / 4, so that the system is critically damped (ie, returns to its
* equilibrium position as quickly as possible, without oscillating), and offset
* the whole thing, such that the equilibrium position is at 0. This gives the
* base solutions
*
* f1(x) = exp(-mx / 2)
* f2(x) = t exp(-mx / 2)
*/
static const double decelFriction = 4;
static const double frameRate = 60;
static const Seconds tickTime = 1_s / frameRate;
static const Seconds minimumTimerInterval { 1_ms };
namespace WebCore {
ScrollAnimationKinetic::PerAxisData::PerAxisData(double lower, double upper, double initialPosition, double initialVelocity)
: m_lower(lower)
, m_upper(upper)
, m_coef1(initialVelocity / decelFriction + initialPosition)
, m_coef2(-initialVelocity / decelFriction)
, m_position(clampTo(initialPosition, lower, upper))
, m_velocity(initialPosition < lower || initialPosition > upper ? 0 : initialVelocity)
{
}
bool ScrollAnimationKinetic::PerAxisData::animateScroll(Seconds timeDelta)
{
auto lastPosition = m_position;
auto lastTime = m_elapsedTime;
m_elapsedTime += timeDelta;
double exponentialPart = exp(-decelFriction * m_elapsedTime.value());
m_position = m_coef1 + m_coef2 * exponentialPart;
m_velocity = -decelFriction * m_coef2 * exponentialPart;
if (m_position < m_lower) {
m_position = m_lower;
m_velocity = 0;
} else if (m_position > m_upper) {
m_position = m_upper;
m_velocity = 0;
} else if (fabs(m_velocity) < 1 || (lastTime && fabs(m_position - lastPosition) < 1)) {
m_position = round(m_position);
m_velocity = 0;
}
return m_velocity;
}
ScrollAnimationKinetic::ScrollAnimationKinetic(ScrollableArea& scrollableArea, std::function<void(FloatPoint&&)>&& notifyPositionChangedFunction)
: ScrollAnimation(scrollableArea)
, m_notifyPositionChangedFunction(WTFMove(notifyPositionChangedFunction))
, m_animationTimer(*this, &ScrollAnimationKinetic::animationTimerFired)
{
}
ScrollAnimationKinetic::~ScrollAnimationKinetic()
{
}
void ScrollAnimationKinetic::stop()
{
m_animationTimer.stop();
m_horizontalData = std::nullopt;
m_verticalData = std::nullopt;
}
void ScrollAnimationKinetic::start(const FloatPoint& initialPosition, const FloatPoint& velocity, bool mayHScroll, bool mayVScroll)
{
stop();
m_position = initialPosition;
if (!velocity.x() && !velocity.y())
return;
if (mayHScroll) {
m_horizontalData = PerAxisData(m_scrollableArea.minimumScrollPosition().x(),
m_scrollableArea.maximumScrollPosition().x(),
initialPosition.x(), velocity.x());
}
if (mayVScroll) {
m_verticalData = PerAxisData(m_scrollableArea.minimumScrollPosition().y(),
m_scrollableArea.maximumScrollPosition().y(),
initialPosition.y(), velocity.y());
}
m_startTime = MonotonicTime::now() - tickTime / 2.;
animationTimerFired();
}
void ScrollAnimationKinetic::animationTimerFired()
{
MonotonicTime currentTime = MonotonicTime::now();
Seconds deltaToNextFrame = 1_s * ceil((currentTime - m_startTime).value() * frameRate) / frameRate - (currentTime - m_startTime);
if (m_horizontalData && !m_horizontalData.value().animateScroll(deltaToNextFrame))
m_horizontalData = std::nullopt;
if (m_verticalData && !m_verticalData.value().animateScroll(deltaToNextFrame))
m_verticalData = std::nullopt;
// If one of the axes didn't finish its animation we must continue it.
if (m_horizontalData || m_verticalData)
m_animationTimer.startOneShot(std::max(minimumTimerInterval, deltaToNextFrame));
double x = m_horizontalData ? m_horizontalData.value().position() : m_position.x();
double y = m_verticalData ? m_verticalData.value().position() : m_position.y();
m_position = FloatPoint(x, y);
m_notifyPositionChangedFunction(FloatPoint(m_position));
}
} // namespace WebCore
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