Audio笔记之EffectChain::process_l

// Must be called with EffectChain::mLock locked
void AudioFlinger::EffectChain::process_l()
{
    sp<ThreadBase> thread = mThread.promote();
    if (thread == 0) {
        ALOGW("process_l(): cannot promote mixer thread");
        return;
    }
    bool isGlobalSession = (mSessionId == AUDIO_SESSION_OUTPUT_MIX) ||
            (mSessionId == AUDIO_SESSION_OUTPUT_STAGE);
    // never process effects when:
    // - on an OFFLOAD thread
    // - no more tracks are on the session and the effect tail has been rendered
    bool doProcess = (thread->type() != ThreadBase::OFFLOAD);
    //1、对于非全局effect，如果没有关联的track且tailBuffCount为0，则不使用音效
    //  每次新增激活track，都会将tailBuffCount置为MaxCount，所以当激活track
    //  数量不为0时，tailBuffCount肯定大于0，因此当有激活track存在时，一定会
    //  执行音效处理，如果没有激活track存在时，如果有关联的track，虽然调用了音效
    //  处理，但实际上输入已经经过清理了，所以不影响输出
    //2、对于全局effect，无需关系track状态，直接对MixBuff中的数据进行处理
    if (!isGlobalSession) {
        bool tracksOnSession = (trackCnt() != 0);

        if (!tracksOnSession && mTailBufferCount == 0) {
            doProcess = false;
        }
        // 如果与effect关联的track都没有激活
        if (activeTrackCnt() == 0) {
            // if no track is active and the effect tail has not been rendered,
            // the input buffer must be cleared here as the mixer process will not do it
            if (tracksOnSession || mTailBufferCount > 0) {
                clearInputBuffer_l(thread);
                if (mTailBufferCount > 0) {
                    mTailBufferCount--;
                }
            }
        }
    }

    size_t size = mEffects.size();
    if (doProcess) {
        for (size_t i = 0; i < size; i++) {
            mEffects[i]->process();
        }
    }
    for (size_t i = 0; i < size; i++) {
        mEffects[i]->updateState();
    }
}

void AudioFlinger::EffectModule::process()
{
    Mutex::Autolock _l(mLock);

    if (mState == DESTROYED || mEffectInterface == NULL ||
            mConfig.inputCfg.buffer.raw == NULL ||
            mConfig.outputCfg.buffer.raw == NULL) {
        return;
    }
    // 1、如果该effect可用，则调用effect engine进行数据处理，并将其写入输出
    // 2、如果该effect不可用，且属于insert类型并处于Chain的尾端，则需要
    //    将其输入填充到其输出，否则该Chain的数据无法送到mMixBuff中，如果
    //    effect不是在尾端，则其输入和输出相同，无需进行额外的填充
    if (isProcessEnabled()) {
        // do 32 bit to 16 bit conversion for auxiliary effect input buffer
        if ((mDescriptor.flags & EFFECT_FLAG_TYPE_MASK) == EFFECT_FLAG_TYPE_AUXILIARY) {
            ditherAndClamp(mConfig.inputCfg.buffer.s32,
                                        mConfig.inputCfg.buffer.s32,
                                        mConfig.inputCfg.buffer.frameCount/2);
        }

        // do the actual processing in the effect engine
        int ret = (*mEffectInterface)->process(mEffectInterface,
                                               &mConfig.inputCfg.buffer,
                                               &mConfig.outputCfg.buffer);

        // force transition to IDLE state when engine is ready
        if (mState == STOPPED && ret == -ENODATA) {
            mDisableWaitCnt = 1;
        }

        // clear auxiliary effect input buffer for next accumulation
        if ((mDescriptor.flags & EFFECT_FLAG_TYPE_MASK) == EFFECT_FLAG_TYPE_AUXILIARY) {
            memset(mConfig.inputCfg.buffer.raw, 0,
                   mConfig.inputCfg.buffer.frameCount*sizeof(int32_t));
        }
    } else if ((mDescriptor.flags & EFFECT_FLAG_TYPE_MASK) == EFFECT_FLAG_TYPE_INSERT &&
                mConfig.inputCfg.buffer.raw != mConfig.outputCfg.buffer.raw) {
        // If an insert effect is idle and input buffer is different from output buffer,
        // accumulate input onto output
        sp<EffectChain> chain = mChain.promote();
        if (chain != 0 && chain->activeTrackCnt() != 0) {
            size_t frameCnt = mConfig.inputCfg.buffer.frameCount * 2;  //always stereo here
            int16_t *in = mConfig.inputCfg.buffer.s16;
            int16_t *out = mConfig.outputCfg.buffer.s16;
            for (size_t i = 0; i < frameCnt; i++) {
                out[i] = clamp16((int32_t)out[i] + (int32_t)in[i]);
            }
        }
    }
}
bool AudioFlinger::EffectModule::isProcessEnabled() const
{
    if (mStatus != NO_ERROR) {
        return false;
    }

    switch (mState) {
    case RESTART:
    case ACTIVE:
    case STOPPING:
    case STOPPED:
        return true;
    case IDLE:
    case STARTING:
    case DESTROYED:
    default:
        return false;
    }
}
static inline int16_t clamp16(int32_t sample)
{
    if ((sample>>15) ^ (sample>>31))
        sample = 0x7FFF ^ (sample>>31);
    return sample;
}
void AudioFlinger::EffectModule::updateState() {
    Mutex::Autolock _l(mLock);

    switch (mState) {
    case RESTART:
        reset_l();
        // FALL THROUGH

    case STARTING:
        // clear auxiliary effect input buffer for next accumulation
        if ((mDescriptor.flags & EFFECT_FLAG_TYPE_MASK) == EFFECT_FLAG_TYPE_AUXILIARY) {
            memset(mConfig.inputCfg.buffer.raw,
                   0,
                   mConfig.inputCfg.buffer.frameCount*sizeof(int32_t));
        }
        if (start_l() == NO_ERROR) {
            mState = ACTIVE;
        } else {
            mState = IDLE;
        }
        break;
    case STOPPING:
        if (stop_l() == NO_ERROR) {
            mDisableWaitCnt = mMaxDisableWaitCnt;
        } else {
            mDisableWaitCnt = 1; // will cause immediate transition to IDLE
        }
        mState = STOPPED;
        break;
    case STOPPED:
        // mDisableWaitCnt is forced to 1 by process() when the engine indicates the end of the
        // turn off sequence.
        if (--mDisableWaitCnt == 0) {
            reset_l();
            mState = IDLE;
        }
        break;
    default: //IDLE , ACTIVE, DESTROYED
        break;
    }
}