third_party/WebKit/Source/platform/animation/TimingFunction.cpp

// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "platform/animation/TimingFunction.h"

#include "platform/animation/CubicBezierControlPoints.h"
#include "wtf/MathExtras.h"

namespace blink {

String LinearTimingFunction::toString() const
{
    return "linear";
}

double LinearTimingFunction::evaluate(double fraction, double) const
{
    return fraction;
}

void LinearTimingFunction::range(double* minValue, double* maxValue) const
{
}

String CubicBezierTimingFunction::toString() const
{
    switch (this->getEaseType()) {
    case CubicBezierTimingFunction::EaseType::EASE:
        return "ease";
    case CubicBezierTimingFunction::EaseType::EASE_IN:
        return "ease-in";
    case CubicBezierTimingFunction::EaseType::EASE_OUT:
        return "ease-out";
    case CubicBezierTimingFunction::EaseType::EASE_IN_OUT:
        return "ease-in-out";
    case CubicBezierTimingFunction::EaseType::CUSTOM:
        return "cubic-bezier(" + String::numberToStringECMAScript(this->x1()) + ", " +
            String::numberToStringECMAScript(this->y1()) + ", " + String::numberToStringECMAScript(this->x2()) +
            ", " + String::numberToStringECMAScript(this->y2()) + ")";
    default:
        NOTREACHED();
        return "";
    }
}

double CubicBezierTimingFunction::evaluate(double fraction, double accuracy) const
{
    return m_bezier.SolveWithEpsilon(fraction, accuracy);
}

// This works by taking taking the derivative of the cubic bezier, on the y
// axis. We can then solve for where the derivative is zero to find the min
// and max distace along the line. We the have to solve those in terms of time
// rather than distance on the x-axis
void CubicBezierTimingFunction::range(double* minValue, double* maxValue) const
{
    if (0 <= m_y1 && m_y2 < 1 && 0 <= m_y2 && m_y2 <= 1) {
        return;
    }

    double a = 3.0 * (m_y1 - m_y2) + 1.0;
    double b = 2.0 * (m_y2 - 2.0 * m_y1);
    double c = m_y1;

    if (std::abs(a) < std::numeric_limits<double>::epsilon()
        && std::abs(b) < std::numeric_limits<double>::epsilon()) {
        return;
    }

    double t1 = 0.0;
    double t2 = 0.0;

    if (std::abs(a) < std::numeric_limits<double>::epsilon()) {
        t1 = -c / b;
    } else {
        double discriminant = b * b - 4 * a * c;
        if (discriminant < 0)
            return;
        double discriminantSqrt = sqrt(discriminant);
        t1 = (-b + discriminantSqrt) / (2 * a);
        t2 = (-b - discriminantSqrt) / (2 * a);
    }

    double solution1 = 0.0;
    double solution2 = 0.0;

    // If the solution is in the range [0,1] then we include it, otherwise we
    // ignore it.

    // An interesting fact about these beziers is that they are only
    // actually evaluated in [0,1]. After that we take the tangent at that point
    // and linearly project it out.
    if (0 < t1 && t1 < 1)
        solution1 = m_bezier.SampleCurveY(t1);

    if (0 < t2 && t2 < 1)
        solution2 = m_bezier.SampleCurveY(t2);

    // Since our input values can be out of the range 0->1 so we must also
    // consider the minimum and maximum points.
    double solutionMin = m_bezier.SolveWithEpsilon(*minValue, std::numeric_limits<double>::epsilon());
    double solutionMax = m_bezier.SolveWithEpsilon(*maxValue, std::numeric_limits<double>::epsilon());
    *minValue = std::min(std::min(solutionMin, solutionMax), 0.0);
    *maxValue = std::max(std::max(solutionMin, solutionMax), 1.0);
    *minValue = std::min(std::min(*minValue, solution1), solution2);
    *maxValue = std::max(std::max(*maxValue, solution1), solution2);
}

String StepsTimingFunction::toString() const
{
    const char* positionString = nullptr;
    switch (getStepPosition()) {
    case StepPosition::START:
        positionString = "start";
        break;
    case StepPosition::MIDDLE:
        positionString = "middle";
        break;
    case StepPosition::END:
        positionString = "end";
        break;
    }

    StringBuilder builder;
    if (this->numberOfSteps() == 1) {
        builder.append("step-");
        builder.append(positionString);
    } else {
        builder.append("steps(");
        builder.append(String::numberToStringECMAScript(this->numberOfSteps()));
        builder.append(", ");
        builder.append(positionString);
        builder.append(')');
    }
    return builder.toString();
}

void StepsTimingFunction::range(double* minValue, double* maxValue) const
{
    *minValue = 0;
    *maxValue = 1;
}

double StepsTimingFunction::evaluate(double fraction, double) const
{
    double startOffset = 0;
    switch (m_stepPosition) {
    case StepPosition::START:
        startOffset = 1;
        break;
    case StepPosition::MIDDLE:
        startOffset = 0.5;
        break;
    case StepPosition::END:
        startOffset = 0;
        break;
    }
    return clampTo(floor((m_steps * fraction) + startOffset) / m_steps, 0.0, 1.0);
}

// Equals operators
bool operator==(const LinearTimingFunction& lhs, const TimingFunction& rhs)
{
    return rhs.type() == TimingFunction::kLinearFunction;
}

bool operator==(const CubicBezierTimingFunction& lhs, const TimingFunction& rhs)
{
    if (rhs.type() != TimingFunction::kCubicBezierFunction)
        return false;

    const CubicBezierTimingFunction& ctf = toCubicBezierTimingFunction(rhs);
    if ((lhs.getEaseType() == CubicBezierTimingFunction::EaseType::CUSTOM) && (ctf.getEaseType() == CubicBezierTimingFunction::EaseType::CUSTOM))
        return (lhs.x1() == ctf.x1()) && (lhs.y1() == ctf.y1()) && (lhs.x2() == ctf.x2()) && (lhs.y2() == ctf.y2());

    return lhs.getEaseType() == ctf.getEaseType();
}

bool operator==(const StepsTimingFunction& lhs, const TimingFunction& rhs)
{
    if (rhs.type() != TimingFunction::kStepsFunction)
        return false;

    const StepsTimingFunction& stf = toStepsTimingFunction(rhs);
    return (lhs.numberOfSteps() == stf.numberOfSteps()) && (lhs.getStepPosition() == stf.getStepPosition());
}

// The generic operator== *must* come after the
// non-generic operator== otherwise it will end up calling itself.
bool operator==(const TimingFunction& lhs, const TimingFunction& rhs)
{
    switch (lhs.type()) {
    case TimingFunction::kLinearFunction: {
        const LinearTimingFunction& linear = toLinearTimingFunction(lhs);
        return (linear == rhs);
    }
    case TimingFunction::kCubicBezierFunction: {
        const CubicBezierTimingFunction& cubic = toCubicBezierTimingFunction(lhs);
        return (cubic == rhs);
    }
    case TimingFunction::kStepsFunction: {
        const StepsTimingFunction& step = toStepsTimingFunction(lhs);
        return (step == rhs);
    }
    default:
        ASSERT_NOT_REACHED();
    }
    return false;
}

// No need to define specific operator!= as they can all come via this function.
bool operator!=(const TimingFunction& lhs, const TimingFunction& rhs)
{
    return !(lhs == rhs);
}

} // namespace blink