flutter_flutter/engine/core/animation/TimingCalculations.h

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#ifndef SKY_ENGINE_CORE_ANIMATION_TIMINGCALCULATIONS_H_
#define SKY_ENGINE_CORE_ANIMATION_TIMINGCALCULATIONS_H_

#include "sky/engine/core/animation/AnimationNode.h"
#include "sky/engine/core/animation/Timing.h"
#include "sky/engine/platform/animation/AnimationUtilities.h"
#include "sky/engine/wtf/MathExtras.h"

namespace blink {

static inline double multiplyZeroAlwaysGivesZero(double x, double y)
{
    ASSERT(!isNull(x));
    ASSERT(!isNull(y));
    return x && y ? x * y : 0;
}

static inline AnimationNode::Phase calculatePhase(double activeDuration, double localTime, const Timing& specified)
{
    ASSERT(activeDuration >= 0);
    if (isNull(localTime))
        return AnimationNode::PhaseNone;
    if (localTime < specified.startDelay)
        return AnimationNode::PhaseBefore;
    if (localTime >= specified.startDelay + activeDuration)
        return AnimationNode::PhaseAfter;
    return AnimationNode::PhaseActive;
}

static inline bool isActiveInParentPhase(AnimationNode::Phase parentPhase, Timing::FillMode fillMode)
{
    switch (parentPhase) {
    case AnimationNode::PhaseBefore:
        return fillMode == Timing::FillModeBackwards || fillMode == Timing::FillModeBoth;
    case AnimationNode::PhaseActive:
        return true;
    case AnimationNode::PhaseAfter:
        return fillMode == Timing::FillModeForwards || fillMode == Timing::FillModeBoth;
    default:
        ASSERT_NOT_REACHED();
        return false;
    }
}

static inline double calculateActiveTime(double activeDuration, Timing::FillMode fillMode, double localTime, AnimationNode::Phase parentPhase, AnimationNode::Phase phase, const Timing& specified)
{
    ASSERT(activeDuration >= 0);
    ASSERT(phase == calculatePhase(activeDuration, localTime, specified));

    switch (phase) {
    case AnimationNode::PhaseBefore:
        if (fillMode == Timing::FillModeBackwards || fillMode == Timing::FillModeBoth)
            return 0;
        return nullValue();
    case AnimationNode::PhaseActive:
        if (isActiveInParentPhase(parentPhase, fillMode))
            return localTime - specified.startDelay;
        return nullValue();
    case AnimationNode::PhaseAfter:
        if (fillMode == Timing::FillModeForwards || fillMode == Timing::FillModeBoth)
            return activeDuration;
        return nullValue();
    case AnimationNode::PhaseNone:
        ASSERT(isNull(localTime));
        return nullValue();
    default:
        ASSERT_NOT_REACHED();
        return nullValue();
    }
}

static inline double calculateScaledActiveTime(double activeDuration, double activeTime, double startOffset, const Timing& specified)
{
    ASSERT(activeDuration >= 0);
    ASSERT(startOffset >= 0);

    if (isNull(activeTime))
        return nullValue();

    ASSERT(activeTime >= 0 && activeTime <= activeDuration);
    return multiplyZeroAlwaysGivesZero(specified.playbackRate < 0 ? activeTime - activeDuration : activeTime, specified.playbackRate) + startOffset;
}

static inline bool endsOnIterationBoundary(double iterationCount, double iterationStart)
{
    ASSERT(std::isfinite(iterationCount));
    return !fmod(iterationCount + iterationStart, 1);
}

static inline double calculateIterationTime(double iterationDuration, double repeatedDuration, double scaledActiveTime, double startOffset, const Timing& specified)
{
    ASSERT(iterationDuration > 0);
    ASSERT(repeatedDuration == multiplyZeroAlwaysGivesZero(iterationDuration, specified.iterationCount));

    if (isNull(scaledActiveTime))
        return nullValue();

    ASSERT(scaledActiveTime >= 0);
    ASSERT(scaledActiveTime <= repeatedDuration + startOffset);

    if (!std::isfinite(scaledActiveTime)
        || (scaledActiveTime - startOffset == repeatedDuration && specified.iterationCount && endsOnIterationBoundary(specified.iterationCount, specified.iterationStart)))
        return iterationDuration;

    ASSERT(std::isfinite(scaledActiveTime));
    return fmod(scaledActiveTime, iterationDuration);
}

static inline double calculateCurrentIteration(double iterationDuration, double iterationTime, double scaledActiveTime, const Timing& specified)
{
    ASSERT(iterationDuration > 0);
    ASSERT(isNull(iterationTime) || iterationTime >= 0);

    if (isNull(scaledActiveTime))
        return nullValue();

    ASSERT(iterationTime >= 0);
    ASSERT(iterationTime <= iterationDuration);
    ASSERT(scaledActiveTime >= 0);

    if (!scaledActiveTime)
        return 0;

    if (iterationTime == iterationDuration)
        return specified.iterationStart + specified.iterationCount - 1;

    return floor(scaledActiveTime / iterationDuration);
}

static inline double calculateDirectedTime(double currentIteration, double iterationDuration, double iterationTime, const Timing& specified)
{
    ASSERT(isNull(currentIteration) || currentIteration >= 0);
    ASSERT(iterationDuration > 0);

    if (isNull(iterationTime))
        return nullValue();

    ASSERT(currentIteration >= 0);
    ASSERT(iterationTime >= 0);
    ASSERT(iterationTime <= iterationDuration);

    const bool currentIterationIsOdd = fmod(currentIteration, 2) >= 1;
    const bool currentDirectionIsForwards = specified.direction == Timing::PlaybackDirectionNormal
        || (specified.direction == Timing::PlaybackDirectionAlternate && !currentIterationIsOdd)
        || (specified.direction == Timing::PlaybackDirectionAlternateReverse && currentIterationIsOdd);

    return currentDirectionIsForwards ? iterationTime : iterationDuration - iterationTime;
}

static inline double calculateTransformedTime(double currentIteration, double iterationDuration, double iterationTime, const Timing& specified)
{
    ASSERT(isNull(currentIteration) || currentIteration >= 0);
    ASSERT(iterationDuration > 0);
    ASSERT(isNull(iterationTime) || (iterationTime >= 0 && iterationTime <= iterationDuration));

    double directedTime = calculateDirectedTime(currentIteration, iterationDuration, iterationTime, specified);
    if (isNull(directedTime))
        return nullValue();
    if (!std::isfinite(iterationDuration))
        return directedTime;
    double timeFraction = directedTime / iterationDuration;
    ASSERT(timeFraction >= 0 && timeFraction <= 1);
    return multiplyZeroAlwaysGivesZero(iterationDuration, specified.timingFunction->evaluate(timeFraction, accuracyForDuration(iterationDuration)));
}

} // namespace blink

#endif  // SKY_ENGINE_CORE_ANIMATION_TIMINGCALCULATIONS_H_