libs/vibrator/ExternalVibrationUtils.cpp

/*
 * Copyright (C) 2020 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
#include <cstring>

#include <android_os_vibrator.h>

#include <algorithm>
#include <math.h>

#include <vibrator/ExternalVibrationUtils.h>

namespace android::os {

namespace {
static constexpr float HAPTIC_SCALE_VERY_LOW_RATIO = 2.0f / 3.0f;
static constexpr float HAPTIC_SCALE_LOW_RATIO = 3.0f / 4.0f;
static constexpr float HAPTIC_MAX_AMPLITUDE_FLOAT = 1.0f;
static constexpr float SCALE_GAMMA = 0.65f; // Same as VibrationEffect.SCALE_GAMMA

float getOldHapticScaleGamma(HapticLevel level) {
    switch (level) {
    case HapticLevel::VERY_LOW:
        return 2.0f;
    case HapticLevel::LOW:
        return 1.5f;
    case HapticLevel::HIGH:
        return 0.5f;
    case HapticLevel::VERY_HIGH:
        return 0.25f;
    default:
        return 1.0f;
    }
}

float getOldHapticMaxAmplitudeRatio(HapticLevel level) {
    switch (level) {
    case HapticLevel::VERY_LOW:
        return HAPTIC_SCALE_VERY_LOW_RATIO;
    case HapticLevel::LOW:
        return HAPTIC_SCALE_LOW_RATIO;
    case HapticLevel::NONE:
    case HapticLevel::HIGH:
    case HapticLevel::VERY_HIGH:
        return 1.0f;
    default:
        return 0.0f;
    }
}

/* Same as VibrationScaler.SCALE_LEVEL_* */
float getHapticScaleFactor(HapticLevel level) {
    switch (level) {
        case HapticLevel::VERY_LOW:
            return 0.6f;
        case HapticLevel::LOW:
            return 0.8f;
        case HapticLevel::HIGH:
            return 1.2f;
        case HapticLevel::VERY_HIGH:
            return 1.4f;
        default:
            return 1.0f;
    }
}

float applyOldHapticScale(float value, float gamma, float maxAmplitudeRatio) {
    float sign = value >= 0 ? 1.0 : -1.0;
    return powf(fabsf(value / HAPTIC_MAX_AMPLITUDE_FLOAT), gamma)
                * maxAmplitudeRatio * HAPTIC_MAX_AMPLITUDE_FLOAT * sign;
}

float applyNewHapticScale(float value, float scaleFactor) {
    float scale = powf(scaleFactor, 1.0f / SCALE_GAMMA);
    if (scaleFactor <= 1) {
        // Scale down is simply a gamma corrected application of scaleFactor to the intensity.
        // Scale up requires a different curve to ensure the intensity will not become > 1.
        return value * scale;
    }

    float sign = value >= 0 ? 1.0f : -1.0f;
    float extraScale = powf(scaleFactor, 4.0f - scaleFactor);
    float x = fabsf(value) * scale * extraScale;
    float maxX = scale * extraScale; // scaled x for intensity == 1

    float expX = expf(x);
    float expMaxX = expf(maxX);

    // Using f = tanh as the scale up function so the max value will converge.
    // a = 1/f(maxX), used to scale f so that a*f(maxX) = 1 (the value will converge to 1).
    float a = (expMaxX + 1.0f) / (expMaxX - 1.0f);
    float fx = (expX - 1.0f) / (expX + 1.0f);

    return sign * std::clamp(a * fx, 0.0f, 1.0f);
}

void applyHapticScale(float* buffer, size_t length, HapticScale scale) {
    if (scale.isScaleMute()) {
        memset(buffer, 0, length * sizeof(float));
        return;
    }
    if (scale.isScaleNone()) {
        return;
    }
    HapticLevel hapticLevel = scale.getLevel();
    float scaleFactor = getHapticScaleFactor(hapticLevel);
    float adaptiveScaleFactor = scale.getAdaptiveScaleFactor();
    float oldGamma = getOldHapticScaleGamma(hapticLevel);
    float oldMaxAmplitudeRatio = getOldHapticMaxAmplitudeRatio(hapticLevel);

    for (size_t i = 0; i < length; i++) {
        if (hapticLevel != HapticLevel::NONE) {
            if (android_os_vibrator_fix_audio_coupled_haptics_scaling()) {
                buffer[i] = applyNewHapticScale(buffer[i], scaleFactor);
            } else {
                buffer[i] = applyOldHapticScale(buffer[i], oldGamma, oldMaxAmplitudeRatio);
            }
        }

        if (adaptiveScaleFactor != 1.0f) {
            buffer[i] *= adaptiveScaleFactor;
        }
    }
}

void clipHapticData(float* buffer, size_t length, float limit) {
    if (isnan(limit) || limit == 0) {
        return;
    }
    limit = fabsf(limit);
    for (size_t i = 0; i < length; i++) {
        float sign = buffer[i] >= 0 ? 1.0 : -1.0;
        if (fabsf(buffer[i]) > limit) {
            buffer[i] = limit * sign;
        }
    }
}

} // namespace

bool isValidHapticScale(HapticScale scale) {
    switch (scale.getLevel()) {
    case HapticLevel::MUTE:
    case HapticLevel::VERY_LOW:
    case HapticLevel::LOW:
    case HapticLevel::NONE:
    case HapticLevel::HIGH:
    case HapticLevel::VERY_HIGH:
        return true;
    }
    return false;
}

void scaleHapticData(float* buffer, size_t length, HapticScale scale, float limit) {
    if (isValidHapticScale(scale)) {
        applyHapticScale(buffer, length, scale);
    }
    clipHapticData(buffer, length, limit);
}

} // namespace android::os