android10 audio音量曲线
一、音量曲线的加载流程
xref: /frameworks/av/services/audiopolicy/managerdefault/AudioPolicyManager.cpp
AudioPolicyManager::AudioPolicyManager(AudioPolicyClientInterface *clientInterface)
: AudioPolicyManager(clientInterface, false /*forTesting*/)
{
loadConfig();
initialize();
}在AudioPolicyManager.cpp的构造函数里面会执行loadConfig和initialize两个方法。
void AudioPolicyManager::loadConfig() {
if (deserializeAudioPolicyXmlConfig(getConfig()) != NO_ERROR) {
ALOGE("could not load audio policy configuration file, setting defaults");
getConfig().setDefault();
}
}在loadConfig方法中调用deserializeAudioPolicyXmlConfig方法去解析配置文件
static status_t deserializeAudioPolicyXmlConfig(AudioPolicyConfig &config) {
char audioPolicyXmlConfigFile[AUDIO_POLICY_XML_CONFIG_FILE_PATH_MAX_LENGTH];
std::vector<const char*> fileNames;
status_t ret;
if (property_get_bool("ro.bluetooth.a2dp_offload.supported", false)) {
if (property_get_bool("persist.bluetooth.bluetooth_audio_hal.disabled", false) &&
property_get_bool("persist.bluetooth.a2dp_offload.disabled", false)) {
// Both BluetoothAudio@2.0 and BluetoothA2dp@1.0 (Offlaod) are disabled, and uses
// the legacy hardware module for A2DP and hearing aid.
fileNames.push_back(AUDIO_POLICY_BLUETOOTH_LEGACY_HAL_XML_CONFIG_FILE_NAME);
} else if (property_get_bool("persist.bluetooth.a2dp_offload.disabled", false)) {
// A2DP offload supported but disabled: try to use special XML file
fileNames.push_back(AUDIO_POLICY_A2DP_OFFLOAD_DISABLED_XML_CONFIG_FILE_NAME);
}
} else if (property_get_bool("persist.bluetooth.bluetooth_audio_hal.disabled", false)) {
fileNames.push_back(AUDIO_POLICY_BLUETOOTH_LEGACY_HAL_XML_CONFIG_FILE_NAME);
}
fileNames.push_back(AUDIO_POLICY_XML_CONFIG_FILE_NAME);
for (const char* fileName : fileNames) {
for (int i = 0; i < kConfigLocationListSize; i++) {
snprintf(audioPolicyXmlConfigFile, sizeof(audioPolicyXmlConfigFile),
"%s/%s", kConfigLocationList[i], fileName);
ret = deserializeAudioPolicyFile(audioPolicyXmlConfigFile, &config);
if (ret == NO_ERROR) {
config.setSource(audioPolicyXmlConfigFile);
return ret;
}
}
}
return ret;
}AUDIO_POLICY_XML_CONFIG_FILE_NAME文件就是audio_policy_configuration.xml
#define AUDIO_POLICY_XML_CONFIG_FILE_NAME "audio_policy_configuration.xml"xref: /frameworks/av/services/audiopolicy/config/audio_policy_configuration.xml
<audioPolicyConfiguration version="1.0" xmlns:xi="http://www.w3.org/2001/XInclude">
............................................................................
<xi:include href="audio_policy_volumes.xml"/>
<xi:include href="default_volume_tables.xml"/>
............................................................................
</audioPolicyConfiguration>在audio_policy_configuration.xml文件里面通过include包含了audio_policy_volumes.xml和default_volume_tables.xml
xref: /frameworks/av/services/audiopolicy/config/audio_policy_volumes.xml
<volume stream="AUDIO_STREAM_RING" deviceCategory="DEVICE_CATEGORY_EARPIECE"
ref="DEFAULT_DEVICE_CATEGORY_EARPIECE_VOLUME_CURVE"/>
<volume stream="AUDIO_STREAM_RING" deviceCategory="DEVICE_CATEGORY_EXT_MEDIA"
ref="DEFAULT_DEVICE_CATEGORY_EXT_MEDIA_VOLUME_CURVE"/>
<volume stream="AUDIO_STREAM_RING" deviceCategory="DEVICE_CATEGORY_HEARING_AID"
ref="DEFAULT_HEARING_AID_VOLUME_CURVE"/>
<volume stream="AUDIO_STREAM_MUSIC" deviceCategory="DEVICE_CATEGORY_HEADSET"
ref="DEFAULT_MEDIA_VOLUME_CURVE"/>
<volume stream="AUDIO_STREAM_MUSIC" deviceCategory="DEVICE_CATEGORY_SPEAKER"
ref="DEFAULT_DEVICE_CATEGORY_SPEAKER_VOLUME_CURVE"/>
<volume stream="AUDIO_STREAM_MUSIC" deviceCategory="DEVICE_CATEGORY_EARPIECE"
ref="DEFAULT_MEDIA_VOLUME_CURVE"/>
<volume stream="AUDIO_STREAM_MUSIC" deviceCategory="DEVICE_CATEGORY_EXT_MEDIA"
ref="DEFAULT_MEDIA_VOLUME_CURVE"/>
<volume stream="AUDIO_STREAM_MUSIC" deviceCategory="DEVICE_CATEGORY_HEARING_AID"
ref="DEFAULT_HEARING_AID_VOLUME_CURVE"/>
<volume stream="AUDIO_STREAM_ALARM" deviceCategory="DEVICE_CATEGORY_HEADSET"
ref="DEFAULT_NON_MUTABLE_HEADSET_VOLUME_CURVE"/>
<volume stream="AUDIO_STREAM_ALARM" deviceCategory="DEVICE_CATEGORY_SPEAKER">
<point>0,-2970</point>
<point>33,-2010</point>
<point>66,-1020</point>
<point>100,0</point>
</volume>在audio_policy_volumes.xml中，规定了音频流类型（stream）、输出设备(deviceCategory)和音量曲线(ref)的关系，在default_volume_tables.xml中规定了具体的音量曲线的值
xref: /frameworks/av/services/audiopolicy/config/default_volume_tables.xml
<reference name="DEFAULT_DEVICE_CATEGORY_EARPIECE_VOLUME_CURVE">
<!--Default Volume Curve -->
<point>1,-4950</point>
<point>33,-3350</point>
<point>66,-1700</point>
<point>100,0</point>
</reference>例如DEFAULT_DEVICE_CATEGORY_EARPIECE_VOLUME_CURVE曲线上的(index、db)值。定义的index范围是1到100， 而db的范围为-4950 到0。音量等级分成4段为100、66、33、1就是音量百分比；0，-1700，-3350，-4950就是对应百分比时衰减的音量，代表衰减-17db，-33.50db，-49.50db。
如果想要修改音频曲线，只要修改default_volume_tables.xml文件就行了。
二、音量调节流程
xref: /frameworks/av/services/audiopolicy/managerdefault/AudioPolicyManager.cpp
status_t AudioPolicyManager::setStreamVolumeIndex(audio_stream_type_t stream,
int index,
audio_devices_t device)
{
auto attributes = mEngine->getAttributesForStreamType(stream);
ALOGV("%s: stream %s attributes=%s", __func__,
toString(stream).c_str(), toString(attributes).c_str());
return setVolumeIndexForAttributes(attributes, index, device);
}调节音量的大小最终会调用到AudioPolicyManager的setStreamVolumeIndex方法。在setStreamVolumeIndex方法中会调用setVolumeIndexForAttributes方法
status_t AudioPolicyManager::setVolumeIndexForAttributes(const audio_attributes_t &attributes,
int index,
audio_devices_t device)
{
// Get Volume group matching the Audio Attributes
auto group = mEngine->getVolumeGroupForAttributes(attributes);
if (group == VOLUME_GROUP_NONE) {
ALOGD("%s: no group matching with %s", __FUNCTION__, toString(attributes).c_str());
return BAD_VALUE;
}
ALOGV("%s: group %d matching with %s", __FUNCTION__, group, toString(attributes).c_str());
status_t status = NO_ERROR;
IVolumeCurves &curves = getVolumeCurves(attributes);
VolumeSource vs = toVolumeSource(group);
product_strategy_t strategy = mEngine->getProductStrategyForAttributes(attributes);
status = setVolumeCurveIndex(index, device, curves);
if (status != NO_ERROR) {
ALOGE("%s failed to set curve index for group %d device 0x%X", __func__, group, device);
return status;
}
audio_devices_t curSrcDevice;
auto curCurvAttrs = curves.getAttributes();
if (!curCurvAttrs.empty() && curCurvAttrs.front() != defaultAttr) {
auto attr = curCurvAttrs.front();
curSrcDevice = mEngine->getOutputDevicesForAttributes(attr, nullptr, false).types();
} else if (!curves.getStreamTypes().empty()) {
auto stream = curves.getStreamTypes().front();
curSrcDevice = mEngine->getOutputDevicesForStream(stream, false).types();
} else {
ALOGE("%s: Invalid src %d: no valid attributes nor stream",__func__, vs);
return BAD_VALUE;
}
curSrcDevice = Volume::getDeviceForVolume(curSrcDevice);
// update volume on all outputs and streams matching the following:
// - The requested stream (or a stream matching for volume control) is active on the output
// - The device (or devices) selected by the engine for this stream includes
// the requested device
// - For non default requested device, currently selected device on the output is either the
// requested device or one of the devices selected by the engine for this stream
// - For default requested device (AUDIO_DEVICE_OUT_DEFAULT_FOR_VOLUME), apply volume only if
// no specific device volume value exists for currently selected device.
for (size_t i = 0; i < mOutputs.size(); i++) {
sp<SwAudioOutputDescriptor> desc = mOutputs.valueAt(i);
audio_devices_t curDevice = desc->devices().types();
if (curDevice & AUDIO_DEVICE_OUT_SPEAKER_SAFE) {
curDevice |= AUDIO_DEVICE_OUT_SPEAKER;
curDevice &= ~AUDIO_DEVICE_OUT_SPEAKER_SAFE;
}
// Inter / intra volume group priority management: Loop on strategies arranged by priority
// If a higher priority strategy is active, and the output is routed to a device with a
// HW Gain management, do not change the volume
bool applyVolume = false;
if (desc->useHwGain()) {
if (!(desc->isActive(toVolumeSource(group)) || isInCall())) {
continue;
}
for (const auto &productStrategy : mEngine->getOrderedProductStrategies()) {
auto activeClients = desc->clientsList(true /*activeOnly*/, productStrategy,
false /*preferredDevice*/);
if (activeClients.empty()) {
continue;
}
bool isPreempted = false;
bool isHigherPriority = productStrategy < strategy;
for (const auto &client : activeClients) {
if (isHigherPriority && (client->volumeSource() != vs)) {
ALOGV("%s: Strategy=%d (\nrequester:\n"
" group %d, volumeGroup=%d attributes=%s)\n"
" higher priority source active:\n"
" volumeGroup=%d attributes=%s) \n"
" on output %zu, bailing out", __func__, productStrategy,
group, group, toString(attributes).c_str(),
client->volumeSource(), toString(client->attributes()).c_str(), i);
applyVolume = false;
isPreempted = true;
break;
}
// However, continue for loop to ensure no higher prio clients running on output
if (client->volumeSource() == vs) {
applyVolume = true;
}
}
if (isPreempted || applyVolume) {
break;
}
}
if (!applyVolume) {
continue; // next output
}
status_t volStatus = checkAndSetVolume(curves, vs, index, desc, curDevice,
(vs == toVolumeSource(AUDIO_STREAM_SYSTEM)?
TOUCH_SOUND_FIXED_DELAY_MS : 0));
if (volStatus != NO_ERROR) {
status = volStatus;
}
continue;
}
if (!(desc->isActive(vs) || isInCall())) {
continue;
}
if ((device != AUDIO_DEVICE_OUT_DEFAULT_FOR_VOLUME) && ((curDevice & device) == 0)) {
continue;
}
if (device != AUDIO_DEVICE_OUT_DEFAULT_FOR_VOLUME) {
curSrcDevice |= device;
applyVolume = (Volume::getDeviceForVolume(curDevice) & curSrcDevice) != 0;
} else {
applyVolume = !curves.hasVolumeIndexForDevice(curSrcDevice);
}
if (applyVolume) {
//FIXME: workaround for truncated touch sounds
// delayed volume change for system stream to be removed when the problem is
// handled by system UI
status_t volStatus = checkAndSetVolume(
curves, vs, index, desc, curDevice,
((vs == toVolumeSource(AUDIO_STREAM_SYSTEM))?
TOUCH_SOUND_FIXED_DELAY_MS : 0));
if (volStatus != NO_ERROR) {
status = volStatus;
}
}
}
mpClientInterface->onAudioVolumeGroupChanged(group, 0 /*flags*/);
return status;
}
在setVolumeIndexForAttributes方法中会调用checkAndSetVolume方法
status_t AudioPolicyManager::checkAndSetVolume(IVolumeCurves &curves,
VolumeSource volumeSource,
int index,
const sp<AudioOutputDescriptor>& outputDesc,
audio_devices_t device,
int delayMs,
bool force)
{
// do not change actual attributes volume if the attributes is muted
if (outputDesc->isMuted(volumeSource)) {
ALOGVV("%s: volume source %d muted count %d active=%d", __func__, volumeSource,
outputDesc->getMuteCount(volumeSource), outputDesc->isActive(volumeSource));
return NO_ERROR;
}
VolumeSource callVolSrc = toVolumeSource(AUDIO_STREAM_VOICE_CALL);
VolumeSource btScoVolSrc = toVolumeSource(AUDIO_STREAM_BLUETOOTH_SCO);
bool isVoiceVolSrc = callVolSrc == volumeSource;
bool isBtScoVolSrc = btScoVolSrc == volumeSource;
audio_policy_forced_cfg_t forceUseForComm =
mEngine->getForceUse(AUDIO_POLICY_FORCE_FOR_COMMUNICATION);
// do not change in call volume if bluetooth is connected and vice versa
// if sco and call follow same curves, bypass forceUseForComm
if ((callVolSrc != btScoVolSrc) &&
((isVoiceVolSrc && forceUseForComm == AUDIO_POLICY_FORCE_BT_SCO) ||
(isBtScoVolSrc && forceUseForComm != AUDIO_POLICY_FORCE_BT_SCO))) {
ALOGV("%s cannot set volume group %d volume with force use = %d for comm", __func__,
volumeSource, forceUseForComm);
return INVALID_OPERATION;
}
if (device == AUDIO_DEVICE_NONE) {
device = outputDesc->devices().types();
}
float volumeDb = computeVolume(curves, volumeSource, index, device);
if (outputDesc->isFixedVolume(device) ||
// Force VoIP volume to max for bluetooth SCO
((isVoiceVolSrc || isBtScoVolSrc) && (device & AUDIO_DEVICE_OUT_ALL_SCO) != 0)) {
volumeDb = 0.0f;
}
outputDesc->setVolume(volumeDb, volumeSource, curves.getStreamTypes(), device, delayMs, force);
if (isVoiceVolSrc || isBtScoVolSrc) {
float voiceVolume;
// Force voice volume to max or mute for Bluetooth SCO as other attenuations are managed by the headset
if (isVoiceVolSrc) {
voiceVolume = (float)index/(float)curves.getVolumeIndexMax();
} else {
voiceVolume = index == 0 ? 0.0 : 1.0;
}
if (voiceVolume != mLastVoiceVolume) {
mpClientInterface->setVoiceVolume(voiceVolume, delayMs);
mLastVoiceVolume = voiceVolume;
}
}
return NO_ERROR;
}
在checkAndSetVolume方法中调用computeVolume方法
float AudioPolicyManager::computeVolume(IVolumeCurves &curves,
VolumeSource volumeSource,
int index,
audio_devices_t device)
{
float volumeDb = curves.volIndexToDb(Volume::getDeviceCategory(device), index);
// handle the case of accessibility active while a ringtone is playing: if the ringtone is much
// louder than the accessibility prompt, the prompt cannot be heard, thus masking the touch
// exploration of the dialer UI. In this situation, bring the accessibility volume closer to
// the ringtone volume
const auto callVolumeSrc = toVolumeSource(AUDIO_STREAM_VOICE_CALL);
const auto ringVolumeSrc = toVolumeSource(AUDIO_STREAM_RING);
const auto musicVolumeSrc = toVolumeSource(AUDIO_STREAM_MUSIC);
const auto alarmVolumeSrc = toVolumeSource(AUDIO_STREAM_ALARM);
if (volumeSource == toVolumeSource(AUDIO_STREAM_ACCESSIBILITY)
&& (AUDIO_MODE_RINGTONE == mEngine->getPhoneState()) &&
mOutputs.isActive(ringVolumeSrc, 0)) {
auto &ringCurves = getVolumeCurves(AUDIO_STREAM_RING);
const float ringVolumeDb = computeVolume(ringCurves, ringVolumeSrc, index, device);
return ringVolumeDb - 4 > volumeDb ? ringVolumeDb - 4 : volumeDb;
}
// in-call: always cap volume by voice volume + some low headroom
if ((volumeSource != callVolumeSrc && (isInCall() ||
mOutputs.isActiveLocally(callVolumeSrc))) &&
(volumeSource == toVolumeSource(AUDIO_STREAM_SYSTEM) ||
volumeSource == ringVolumeSrc || volumeSource == musicVolumeSrc ||
volumeSource == alarmVolumeSrc ||
volumeSource == toVolumeSource(AUDIO_STREAM_NOTIFICATION) ||
volumeSource == toVolumeSource(AUDIO_STREAM_ENFORCED_AUDIBLE) ||
volumeSource == toVolumeSource(AUDIO_STREAM_DTMF) ||
volumeSource == toVolumeSource(AUDIO_STREAM_ACCESSIBILITY))) {
auto &voiceCurves = getVolumeCurves(callVolumeSrc);
int voiceVolumeIndex = voiceCurves.getVolumeIndex(device);
const float maxVoiceVolDb =
computeVolume(voiceCurves, callVolumeSrc, voiceVolumeIndex, device)
+ IN_CALL_EARPIECE_HEADROOM_DB;
// FIXME: Workaround for call screening applications until a proper audio mode is defined
// to support this scenario : Exempt the RING stream from the audio cap if the audio was
// programmatically muted.
// VOICE_CALL stream has minVolumeIndex > 0 : Users cannot set the volume of voice calls to
// 0. We don't want to cap volume when the system has programmatically muted the voice call
// stream. See setVolumeCurveIndex() for more information.
bool exemptFromCapping = (volumeSource == ringVolumeSrc) && (voiceVolumeIndex == 0);
ALOGV_IF(exemptFromCapping, "%s volume source %d at vol=%f not capped", __func__,
volumeSource, volumeDb);
if ((volumeDb > maxVoiceVolDb) && !exemptFromCapping) {
ALOGV("%s volume source %d at vol=%f overriden by volume group %d at vol=%f", __func__,
volumeSource, volumeDb, callVolumeSrc, maxVoiceVolDb);
volumeDb = maxVoiceVolDb;
}
}
// if a headset is connected, apply the following rules to ring tones and notifications
// to avoid sound level bursts in user's ears:
// - always attenuate notifications volume by 6dB
// - attenuate ring tones volume by 6dB unless music is not playing and
// speaker is part of the select devices
// - if music is playing, always limit the volume to current music volume,
// with a minimum threshold at -36dB so that notification is always perceived.
if ((device & (AUDIO_DEVICE_OUT_BLUETOOTH_A2DP | AUDIO_DEVICE_OUT_BLUETOOTH_A2DP_HEADPHONES |
AUDIO_DEVICE_OUT_WIRED_HEADSET | AUDIO_DEVICE_OUT_WIRED_HEADPHONE |
AUDIO_DEVICE_OUT_USB_HEADSET | AUDIO_DEVICE_OUT_HEARING_AID)) &&
((volumeSource == alarmVolumeSrc ||
volumeSource == ringVolumeSrc) ||
(volumeSource == toVolumeSource(AUDIO_STREAM_NOTIFICATION)) ||
(volumeSource == toVolumeSource(AUDIO_STREAM_SYSTEM)) ||
((volumeSource == toVolumeSource(AUDIO_STREAM_ENFORCED_AUDIBLE)) &&
(mEngine->getForceUse(AUDIO_POLICY_FORCE_FOR_SYSTEM) == AUDIO_POLICY_FORCE_NONE))) &&
curves.canBeMuted()) {
// when the phone is ringing we must consider that music could have been paused just before
// by the music application and behave as if music was active if the last music track was
// just stopped
if (isStreamActive(AUDIO_STREAM_MUSIC, SONIFICATION_HEADSET_MUSIC_DELAY) ||
mLimitRingtoneVolume) {
volumeDb += SONIFICATION_HEADSET_VOLUME_FACTOR_DB;
audio_devices_t musicDevice =
mEngine->getOutputDevicesForAttributes(attributes_initializer(AUDIO_USAGE_MEDIA),
nullptr, true /*fromCache*/).types();
auto &musicCurves = getVolumeCurves(AUDIO_STREAM_MUSIC);
float musicVolDb = computeVolume(musicCurves, musicVolumeSrc,
musicCurves.getVolumeIndex(musicDevice), musicDevice);
float minVolDb = (musicVolDb > SONIFICATION_HEADSET_VOLUME_MIN_DB) ?
musicVolDb : SONIFICATION_HEADSET_VOLUME_MIN_DB;
if (volumeDb > minVolDb) {
volumeDb = minVolDb;
ALOGV("computeVolume limiting volume to %f musicVol %f", minVolDb, musicVolDb);
}
if (device & (AUDIO_DEVICE_OUT_BLUETOOTH_A2DP |
AUDIO_DEVICE_OUT_BLUETOOTH_A2DP_HEADPHONES)) {
// on A2DP, also ensure notification volume is not too low compared to media when
// intended to be played
if ((volumeDb > -96.0f) &&
(musicVolDb - SONIFICATION_A2DP_MAX_MEDIA_DIFF_DB > volumeDb)) {
ALOGV("%s increasing volume for volume source=%d device=0x%X from %f to %f",
__func__, volumeSource, device, volumeDb,
musicVolDb - SONIFICATION_A2DP_MAX_MEDIA_DIFF_DB);
volumeDb = musicVolDb - SONIFICATION_A2DP_MAX_MEDIA_DIFF_DB;
}
}
} else if ((Volume::getDeviceForVolume(device) != AUDIO_DEVICE_OUT_SPEAKER) ||
(!(volumeSource == alarmVolumeSrc || volumeSource == ringVolumeSrc))) {
volumeDb += SONIFICATION_HEADSET_VOLUME_FACTOR_DB;
}
}
return volumeDb;
}在computeVolume方法中调用volIndexToDb方法，volIndexToDb方法定义在VolumeCurve.h头文件中。
xref: /frameworks/av/services/audiopolicy/engine/common/include/VolumeCurve.h
virtual float volIndexToDb(device_category deviceCat, int indexInUi) const
{
sp<VolumeCurve> vc = getCurvesFor(deviceCat);
if (vc != 0) {
return vc->volIndexToDb(indexInUi, mIndexMin, mIndexMax);
} else {
ALOGE("Invalid device category %d for Volume Curve", deviceCat);
return 0.0f;
}
}具体实现类在VolumeCurve.cpp类中
ef: /frameworks/av/services/audiopolicy/engine/common/src/VolumeCurve.cpp
float VolumeCurve::volIndexToDb(int indexInUi, int volIndexMin, int volIndexMax) const
{
ALOG_ASSERT(!mCurvePoints.isEmpty(), "Invalid volume curve");
if (volIndexMin < 0 || volIndexMax < 0) {
// In order to let AudioService initialize the min and max, convention is to use -1
return NAN;
}
if (indexInUi < volIndexMin) {
// an index of 0 means mute request when volIndexMin > 0
if (indexInUi == 0) {
ALOGV("VOLUME forcing mute for index 0 with min index %d", volIndexMin);
return VOLUME_MIN_DB;
}
ALOGV("VOLUME remapping index from %d to min index %d", indexInUi, volIndexMin);
indexInUi = volIndexMin;
} else if (indexInUi > volIndexMax) {
ALOGV("VOLUME remapping index from %d to max index %d", indexInUi, volIndexMax);
indexInUi = volIndexMax;
}
size_t nbCurvePoints = mCurvePoints.size();
// the volume index in the UI is relative to the min and max volume indices for this stream
int nbSteps = 1 + mCurvePoints[nbCurvePoints - 1].mIndex - mCurvePoints[0].mIndex;
int volIdx = (nbSteps * (indexInUi - volIndexMin)) / (volIndexMax - volIndexMin);
// Where would this volume index been inserted in the curve point
size_t indexInUiPosition = mCurvePoints.orderOf(CurvePoint(volIdx, 0));
if (indexInUiPosition >= nbCurvePoints) {
//use last point of table
return mCurvePoints[nbCurvePoints - 1].mAttenuationInMb / 100.0f;
}
if (indexInUiPosition == 0) {
if (indexInUiPosition != mCurvePoints[0].mIndex) {
return VOLUME_MIN_DB; // out of bounds
}
return mCurvePoints[0].mAttenuationInMb / 100.0f;
}
// linear interpolation in the attenuation table in dB
float decibels = (mCurvePoints[indexInUiPosition - 1].mAttenuationInMb / 100.0f) +
((float)(volIdx - mCurvePoints[indexInUiPosition - 1].mIndex)) *
( ((mCurvePoints[indexInUiPosition].mAttenuationInMb / 100.0f) -
(mCurvePoints[indexInUiPosition - 1].mAttenuationInMb / 100.0f)) /
((float)(mCurvePoints[indexInUiPosition].mIndex -
mCurvePoints[indexInUiPosition - 1].mIndex)) );
ALOGV("VOLUME vol index=[%d %d %d], dB=[%.1f %.1f %.1f]",
mCurvePoints[indexInUiPosition - 1].mIndex, volIdx,
mCurvePoints[indexInUiPosition].mIndex,
((float)mCurvePoints[indexInUiPosition - 1].mAttenuationInMb / 100.0f), decibels,
((float)mCurvePoints[indexInUiPosition].mAttenuationInMb / 100.0f));
return decibels;
}在VolumeCurve::volIndexToDb里实现音量曲线的计算。