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Mekanisme notifikasi peristiwa dan frame

Pada rilis Exterior View System (EVS) rilis sebelumnya, IEvsCameraStream menentukan satu metode callback untuk mengirimkan video yang direkam saja frame. Meskipun implementasi klien layanan EVS yang disederhanakan ini, menyulitkan klien untuk mengidentifikasi insiden streaming dan, oleh karena itu, untuk menanganinya dengan benar. Untuk meningkatkan pengalaman pengembangan EVS, AOSP kini berisi callback tambahan untuk mengirim peristiwa streaming.

package android.hardware.automotive.evs@1.1;

import @1.0::IEvsCameraStream;

/**
 * Implemented on client side to receive asynchronous video frame deliveries.
 */
interface IEvsCameraStream extends @1.0::IEvsCameraStream {
    /**
     * Receives calls from the HAL each time a video frame is ready for inspection.
     * Buffer handles received by this method must be returned via calls to
     * IEvsCamera::doneWithFrame_1_1(). When the video stream is stopped via a call
     * to IEvsCamera::stopVideoStream(), this callback may continue to happen for
     * some time as the pipeline drains. Each frame must still be returned.
     * When the last frame in the stream has been delivered, STREAM_STOPPED
     * event must be delivered. No further frame deliveries may happen
     * thereafter.
     *
     * @param buffer a buffer descriptor of a delivered image frame.
     */
    oneway deliverFrame_1_1(BufferDesc buffer);

    /**
     * Receives calls from the HAL each time an event happens.
     *
     * @param  event EVS event with possible event information.
     */
    oneway notify(EvsEvent event);
};

Metode ini menampilkan EvsEventDesc yang terdiri dari tiga kolom:

Jenis peristiwa.
String untuk mengidentifikasi asal peristiwa.
Data word 4x 32-bit untuk memuat kemungkinan informasi peristiwa.

/**
 * Structure that describes informative events occurred during EVS is streaming
 */
struct EvsEvent {
    /**
     * Type of an informative event
     */
    EvsEventType aType;
    /**
     * Device identifier
     */
    string deviceId;
    /**
     * Possible additional information
     */
    uint32_t[4] payload;
};

Dan, untuk menghindari perbedaan dalam deskripsi buffer grafis antara EVS dan komponen grafis Android lainnya, BufferDesc telah didefinisikan ulang menjadi menggunakan HardwareBuffer yang diimpor dari antarmuka android.hardware.graphics.common@1.2. HardwareBuffer berisi HardwareBufferDescription, yang merupakan Versi HIDL dari Android NDK AHardwareBuffer_Desc, dengan handle buffer.

/**
 * HIDL counterpart of AHardwareBuffer_Desc.
 *
 * An AHardwareBuffer_Desc object can be converted to and from a
 * HardwareBufferDescription object by memcpy().
 *
 * @sa +ndk libnativewindow#AHardwareBuffer_Desc.
 */
typedef uint32_t[10] HardwareBufferDescription;

/**
 * HIDL counterpart of AHardwareBuffer.
 *
 * AHardwareBuffer_createFromHandle() can be used to convert a HardwareBuffer
 * object to an AHardwareBuffer object.
 *
 * Conversely, AHardwareBuffer_getNativeHandle() can be used to extract a native
 * handle from an AHardwareBuffer object. Paired with AHardwareBuffer_Desc,
 * AHardwareBuffer_getNativeHandle() can be used to convert between
 * HardwareBuffer and AHardwareBuffer.
 *
 * @sa +ndk libnativewindow#AHardwareBuffer".
 */
struct HardwareBuffer {
    HardwareBufferDescription description;
    handle nativeHandle;
}

/**
 * Structure representing an image buffer through our APIs
 *
 * In addition to the handle to the graphics memory, need to retain
 * the properties of the buffer for easy reference and reconstruction of
 * an ANativeWindowBuffer object on the remote side of API calls.
 * Not least because OpenGL expect an ANativeWindowBuffer* for us as a
 * texture via eglCreateImageKHR().
 */
struct BufferDesc {
    /**
     * HIDL counterpart of AHardwareBuffer_Desc. Please see
     * hardware/interfaces/graphics/common/1.2/types.hal for more details.
     */
    HardwareBuffer buffer;
    /**
     * The size of a pixel in the units of bytes
     */
    uint32_t pixelSize;
    /**
     * Opaque value from driver
     */
    uint32_t bufferId;
    /**
     * Unique identifier of the physical camera device that produces this buffer.
     */
    string deviceId;
    /**
     * Time that this buffer is being filled
     */
    int64_t timestamp;
    /**
     * Frame metadata. This is opaque to EVS manager
     */
    vec<uint8_t> metadata
};

Catatan: HardwareBufferDescription didefinisikan sebagai array yang berisi sepuluh kata 32-bit. Anda dapat mentransmisikannya sebagai jenis AHardwareBuffer_Desc dan isi kontennya.

EvsEventDesc adalah struct dari enum EvsEventType, yang mencantumkan beberapa kejadian streaming dan {i>payload<i} kata 32-bit, di mana pengembang dapat menempatkan kemungkinan informasi tambahan. Misalnya, developer dapat menempatkan kode error untuk peristiwa error streaming.

/**
 * Types of informative streaming events
 */
enum EvsEventType : uint32_t {
    /**
     * Video stream is started
     */
    STREAM_STARTED = 0,
    /**
     * Video stream is stopped
     */
    STREAM_STOPPED,
    /**
     * Video frame is dropped
     */
    FRAME_DROPPED,
    /**
     * Timeout happens
     */
    TIMEOUT,
    /**
     * Camera parameter is changed; payload contains a changed parameter ID and
     * its value
     */
    PARAMETER_CHANGED,
    /**
     * Master role has become available
     */
    MASTER_RELEASED,
};

Pengiriman frame

Dengan BufferDesc baru, IEvsCameraStream juga memperkenalkan metode callback baru untuk menerima frame dan event streaming dari implementasi layanan.

/**
 * Implemented on client side to receive asynchronous streaming event deliveries.
 */
interface IEvsCameraStream extends @1.0::IEvsCameraStream {
   /**
    * Receives calls from the HAL each time video frames are ready for inspection.
    * Buffer handles received by this method must be returned via calls to
    * IEvsCamera::doneWithFrame_1_1(). When the video stream is stopped via a call
    * to IEvsCamera::stopVideoStream(), this callback may continue to happen for
    * some time as the pipeline drains. Each frame must still be returned.
    * When the last frame in the stream has been delivered, STREAM_STOPPED
    * event must be delivered. No further frame deliveries may happen
    * thereafter.
    *
    * A camera device delivers the same number of frames as number of
    * backing physical camera devices; it means, a physical camera device
    * sends always a single frame and a logical camera device sends multiple
    * frames as many as the number of backing physical camera devices.
    *
    * @param buffer Buffer descriptors of delivered image frames.
    */
   oneway deliverFrame_1_1(vec<BufferDesc> buffer);

   /**
    * Receives calls from the HAL each time an event happens.
    *
    * @param  event EVS event with possible event information.
    */
   oneway notify(EvsEventDesc event);
};

Versi lebih baru dari metode callback {i>frame<i} dirancang untuk mengirimkan beberapa deskriptor buffer. Oleh karena itu, implementasi kamera EVS dapat meneruskan beberapa frame dengan satu panggilan jika mengelola beberapa sumber.

Juga, protokol sebelumnya yang memberi tahu akhir {i>streaming<i}, yang mengirimkan frame null, tidak digunakan lagi dan diganti dengan STREAM_STOPPED peristiwa.

Diagram urutan notifikasi peristiwa

Gambar 1. Diagram urutan notifikasi peristiwa

Menggunakan mekanisme notifikasi peristiwa dan frame

Mengidentifikasi versi IEvsCameraStream yang diterapkan oleh klien

Layanan dapat mengidentifikasi versi antarmuka IEvsCameraStream yang masuk yang diterapkan oleh klien dengan mencoba untuk melakukan downcast:

using IEvsCameraStream_1_0 =
    ::android::hardware::automotive::evs::V1_0::IEvsCameraStream;
using IEvsCameraStream_1_1 =
    ::android::hardware::automotive::evs::V1_1::IEvsCameraStream;

Return<EvsResult> EvsV4lCamera::startVideoStream(
    const sp<IEvsCameraStream_1_0>& stream)  {

    IEvsCameraStream_1_0 aStream = stream;
    // Try to downcast. This succeeds if the client implements
    // IEvsCameraStream v1.1.
    IEvsCameraStream_1_1 aStream_1_1 =
        IEvsCameraStream_1_1::castFrom(aStream).withDefault(nullptr);
    if (aStream_1_1 == nullptr) {
        ALOGI("Start a stream for v1.0 client.");
    } else {
        ALOGI("Start a stream for v1.1 client.");
    }

    // Start a video stream
    ...
}

callback pemberitahuan()

EvsEvent diteruskan melalui callback notify() dan klien kemudian dapat mengidentifikasi jenisnya berdasarkan diskriminator, seperti yang ditunjukkan di bawah ini:

Return<void> StreamHandler::notify(const EvsEvent& event) {
    ALOGD("Received an event id: %u", event.aType);
    // Handle each received event.
    switch(event.aType) {
        case EvsEventType::ERROR:
            // Do something to handle an error
            ...
            break;
        [More cases]
    }
    return Void();
}

Menggunakan BufferDesc

AHardwareBuffer_Desc adalah tipe data Android NDK untuk mewakili buffer hardware native yang dapat diikat ke Primitif EGL/OpenGL dan Vulkan. {i>Metadata<i} ini berisi sebagian besar {i>metadata<i} buffer dari BufferDesc EVS dan menggantikannya dalam definisi BufferDesc yang baru. Namun, karena didefinisikan sebagai array dalam antarmuka HIDL, variabel anggota tidak dapat diindeks secara langsung. Sebagai gantinya, Anda dapat mentransmisikan array sebagai jenis AHardwareBuffer_Desc, seperti yang ditunjukkan di bawah ini:

BufferDesc bufDesc = {};
AHardwareBuffer_Desc* pDesc =
    reinterpret_cast<AHardwareBuffer_Desc *>(&bufDesc.buffer.description);
pDesc->width  = mVideo.getWidth();
pDesc->height = mVideo.getHeight();
pDesc->layers = 1;
pDesc->format = mFormat;
pDesc->usage  = mUsage;
pDesc->stride = mStride;
bufDesc_1_1.buffer.nativeHandle = mBuffers[idx].handle;
bufDesc_1_1.bufferId = idx;