elastic_overscroll_controller_bezier.cc

// Copyright 2020 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "third_party/blink/renderer/platform/widget/input/elastic_overscroll_controller_bezier.h"
#include "ui/gfx/geometry/vector2d_conversions.h"

namespace blink {

namespace {
// The following constants are determined experimentally.

// Used to determine how far the scroller is allowed to stretch.
constexpr double kOverscrollBoundaryMultiplier = …;

// Maximum duration for the bounce back animation.
constexpr double kBounceBackMaxDurationMilliseconds = …;

// Time taken by the bounce back animation (in milliseconds) to scroll 1 px.
constexpr double kBounceBackMillisecondsPerPixel = …;

// Threshold above which a forward animation should be played. Stray finger
// movements can cause velocities to be non-zero. This in-turn may lead to minor
// jerks when the bounce back animation is being played. Expressed in pixels per
// second.
constexpr double kIgnoreForwardBounceVelocityThreshold = …;

constexpr double kOverbounceMaxDurationMilliseconds = …;
constexpr double kOverbounceMillisecondsPerPixel = …;
constexpr double kOverbounceDistanceMultiplier = …;

// Control points for the bounce forward Cubic Bezier curve.
constexpr double kBounceForwardsX1 = …;
constexpr double kBounceForwardsY1 = …;
constexpr double kBounceForwardsX2 = …;
constexpr double kBounceForwardsY2 = …;

// Control points for the bounce back Cubic Bezier curve.
constexpr double kBounceBackwardsX1 = …;
constexpr double kBounceBackwardsY1 = …;
constexpr double kBounceBackwardsX2 = …;
constexpr double kBounceBackwardsY2 = …;

base::TimeDelta CalculateBounceForwardsDuration(
    double bounce_forwards_distance) { … }

base::TimeDelta CalculateBounceBackDuration(double bounce_back_distance) { … }
}  // namespace

// Scale one of the control points of the Cubic Bezier curve based on the
// initial_velocity (which is expressed in terms of pixels / ms).
gfx::CubicBezier InitialVelocityBasedBezierCurve(const double initial_velocity,
                                                 const double x1,
                                                 const double y1,
                                                 const double x2,
                                                 const double y2) { … }

ElasticOverscrollControllerBezier::ElasticOverscrollControllerBezier(
    cc::ScrollElasticityHelper* helper)
    : … { … }

// Returns the maximum amount to be overscrolled.
gfx::Vector2dF ElasticOverscrollControllerBezier::OverscrollBoundary(
    const gfx::Size& scroller_bounds) const { … }

void ElasticOverscrollControllerBezier::DidEnterMomentumAnimatedState() { … }

double ElasticOverscrollControllerBezier::StretchAmountForForwardBounce(
    const gfx::CubicBezier bounce_forwards_curve,
    const base::TimeDelta& delta,
    const base::TimeDelta& bounce_forwards_duration,
    const double velocity,
    const double initial_stretch,
    const double bounce_forwards_distance) const { … }

double ElasticOverscrollControllerBezier::StretchAmountForBackwardBounce(
    const gfx::CubicBezier bounce_backwards_curve,
    const base::TimeDelta& delta,
    const base::TimeDelta& bounce_backwards_duration,
    const double bounce_forwards_distance) const { … }

gfx::Vector2d ElasticOverscrollControllerBezier::StretchAmountForTimeDelta(
    const base::TimeDelta& delta) const { … }

// The goal of this calculation is to map the distance the user has scrolled
// past the boundary into the distance to actually scroll the elastic scroller.
gfx::Vector2d
ElasticOverscrollControllerBezier::StretchAmountForAccumulatedOverscroll(
    const gfx::Vector2dF& accumulated_overscroll) const { … }

// This function does the inverse of StretchAmountForAccumulatedOverscroll. As
// in, instead of taking in the amount of distance overscrolled to get the
// bounce distance, it takes in the bounce distance and calculates how much is
// actually overscrolled.
gfx::Vector2d
ElasticOverscrollControllerBezier::AccumulatedOverscrollForStretchAmount(
    const gfx::Vector2dF& stretch_amount) const { … }
}  // namespace blink
chromium/third_party/blink/renderer/platform/widget/input/elastic_overscroll_controller_bezier.cc
