flutter_flutter/sky/engine/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 "flutter/sky/engine/platform/animation/TimingFunction.h"

#include "flutter/sky/engine/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->subType()) {
    case CubicBezierTimingFunction::Ease:
      return "ease";
    case CubicBezierTimingFunction::EaseIn:
      return "ease-in";
    case CubicBezierTimingFunction::EaseOut:
      return "ease-out";
    case CubicBezierTimingFunction::EaseInOut:
      return "ease-in-out";
    case CubicBezierTimingFunction::Custom:
      return "cubic-bezier(" + String::numberToStringECMAScript(this->x1()) +
             ", " + String::numberToStringECMAScript(this->y1()) + ", " +
             String::numberToStringECMAScript(this->x2()) + ", " +
             String::numberToStringECMAScript(this->y2()) + ")";
    default:
      ASSERT_NOT_REACHED();
  }
  return "";
}

double CubicBezierTimingFunction::evaluate(double fraction,
                                           double accuracy) const {
  if (!m_bezier)
    m_bezier = adoptPtr(new UnitBezier(m_x1, m_y1, m_x2, m_y2));
  return m_bezier->solve(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.
  if (!m_bezier)
    m_bezier = adoptPtr(new UnitBezier(m_x1, m_y1, m_x2, m_y2));

  // 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->solve(*minValue, std::numeric_limits<double>::epsilon());
  double solutionMax =
      m_bezier->solve(*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 {
  StringBuilder builder;
  switch (this->subType()) {
    case StepsTimingFunction::Start:
      return "step-start";
    case StepsTimingFunction::Middle:
      return "step-middle";
    case StepsTimingFunction::End:
      return "step-end";
    case StepsTimingFunction::Custom:
      builder.append("steps(" +
                     String::numberToStringECMAScript(this->numberOfSteps()) +
                     ", ");

      if (this->stepAtPosition() == StepsTimingFunction::StepAtStart)
        builder.appendLiteral("start");
      else if (this->stepAtPosition() == StepsTimingFunction::StepAtMiddle)
        builder.appendLiteral("middle");
      else if (this->stepAtPosition() == StepsTimingFunction::StepAtEnd)
        builder.appendLiteral("end");
      else
        ASSERT_NOT_REACHED();

      builder.append(')');
      break;
    default:
      ASSERT_NOT_REACHED();
  }
  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_stepAtPosition) {
    case StepAtStart:
      startOffset = 1;
      break;
    case StepAtMiddle:
      startOffset = 0.5;
      break;
    case StepAtEnd:
      startOffset = 0;
      break;
    default:
      ASSERT_NOT_REACHED();
      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::LinearFunction;
}

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

  const CubicBezierTimingFunction& ctf = toCubicBezierTimingFunction(rhs);
  if ((lhs.subType() == CubicBezierTimingFunction::Custom) &&
      (ctf.subType() == CubicBezierTimingFunction::Custom))
    return (lhs.x1() == ctf.x1()) && (lhs.y1() == ctf.y1()) &&
           (lhs.x2() == ctf.x2()) && (lhs.y2() == ctf.y2());

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

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

  const StepsTimingFunction& stf = toStepsTimingFunction(rhs);
  if ((lhs.subType() == StepsTimingFunction::Custom) &&
      (stf.subType() == StepsTimingFunction::Custom))
    return (lhs.numberOfSteps() == stf.numberOfSteps()) &&
           (lhs.stepAtPosition() == stf.stepAtPosition());

  return lhs.subType() == stf.subType();
}

// 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::LinearFunction: {
      const LinearTimingFunction& linear = toLinearTimingFunction(lhs);
      return (linear == rhs);
    }
    case TimingFunction::CubicBezierFunction: {
      const CubicBezierTimingFunction& cubic = toCubicBezierTimingFunction(lhs);
      return (cubic == rhs);
    }
    case TimingFunction::StepsFunction: {
      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