Source/WebCore/platform/graphics/AnimationFrameRate.cpp

/*
 * Copyright (C) 2020 Apple Inc. All rights reserved.
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 * 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
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 *    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. ``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
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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#include "config.h"
#include "AnimationFrameRate.h"
#include <wtf/text/TextStream.h>

namespace WebCore {

static constexpr OptionSet<ThrottlingReason> halfSpeedThrottlingReasons { ThrottlingReason::LowPowerMode, ThrottlingReason::NonInteractedCrossOriginFrame, ThrottlingReason::VisuallyIdle };

FramesPerSecond framesPerSecondNearestFullSpeed(FramesPerSecond nominalFramesPerSecond)
{
    if (nominalFramesPerSecond <= FullSpeedFramesPerSecond)
        return nominalFramesPerSecond;

    float fullSpeedRatio = nominalFramesPerSecond / FullSpeedFramesPerSecond;
    FramesPerSecond floorSpeed = nominalFramesPerSecond / std::floor(fullSpeedRatio);
    FramesPerSecond ceilSpeed = nominalFramesPerSecond / std::ceil(fullSpeedRatio);

    return fullSpeedRatio - std::floor(fullSpeedRatio) <= 0.5 ? floorSpeed : ceilSpeed;
}

std::optional<FramesPerSecond> preferredFramesPerSecond(OptionSet<ThrottlingReason> reasons, std::optional<FramesPerSecond> nominalFramesPerSecond, bool preferFrameRatesNear60FPS)
{
    if (reasons.contains(ThrottlingReason::OutsideViewport))
        return std::nullopt;

    if (!nominalFramesPerSecond || *nominalFramesPerSecond == FullSpeedFramesPerSecond) {
        // FIXME: handle ThrottlingReason::VisuallyIdle
        if (reasons.containsAny(halfSpeedThrottlingReasons))
            return HalfSpeedThrottlingFramesPerSecond;

        return FullSpeedFramesPerSecond;
    }

    auto framesPerSecond = preferFrameRatesNear60FPS ? framesPerSecondNearestFullSpeed(*nominalFramesPerSecond) : *nominalFramesPerSecond;
    if (reasons.containsAny(halfSpeedThrottlingReasons))
        framesPerSecond /= IntervalThrottlingFactor;

    return framesPerSecond;
}

Seconds preferredFrameInterval(OptionSet<ThrottlingReason> reasons, std::optional<FramesPerSecond> nominalFramesPerSecond, bool preferFrameRatesNear60FPS)
{
    if (reasons.contains(ThrottlingReason::OutsideViewport))
        return AggressiveThrottlingAnimationInterval;

    if (!nominalFramesPerSecond || *nominalFramesPerSecond == FullSpeedFramesPerSecond) {
        // FIXME: handle ThrottlingReason::VisuallyIdle
        if (reasons.containsAny(halfSpeedThrottlingReasons))
            return HalfSpeedThrottlingAnimationInterval;
        return FullSpeedAnimationInterval;
    }

    auto framesPerSecond = preferFrameRatesNear60FPS ? framesPerSecondNearestFullSpeed(*nominalFramesPerSecond) : *nominalFramesPerSecond;
    auto interval = Seconds(1.0 / framesPerSecond);

    if (reasons.containsAny(halfSpeedThrottlingReasons))
        interval *= IntervalThrottlingFactor;

    return interval;
}

FramesPerSecond preferredFramesPerSecondFromInterval(Seconds preferredFrameInterval)
{
    if (preferredFrameInterval == FullSpeedAnimationInterval)
        return FullSpeedFramesPerSecond;

    if (preferredFrameInterval == HalfSpeedThrottlingAnimationInterval)
        return HalfSpeedThrottlingFramesPerSecond;

    return std::round(1 / preferredFrameInterval.seconds());
}

TextStream& operator<<(TextStream& ts, const OptionSet<ThrottlingReason>& reasons)
{
    bool didAppend = false;

    for (auto reason : reasons) {
        if (didAppend)
            ts << "|";
        switch (reason) {
        case ThrottlingReason::VisuallyIdle:
            ts << "VisuallyIdle";
            break;
        case ThrottlingReason::OutsideViewport:
            ts << "OutsideViewport";
            break;
        case ThrottlingReason::LowPowerMode:
            ts << "LowPowerMode";
            break;
        case ThrottlingReason::NonInteractedCrossOriginFrame:
            ts << "NonInteractiveCrossOriginFrame";
            break;
        }
        didAppend = true;
    }

    if (reasons.isEmpty())
        ts << "[Unthrottled]";
    return ts;
}
} // namespace WebCore