本頁面由 Cloud Translation API 翻譯而成。

汽車螢幕 Proxy 服務

這項簡單的架構服務程序會在 HAL 實作中使用 SurfaceFlinger/EGL，但未連結 libgui。Android 開放原始碼計畫提供這項服務的預設實作方式，以及功能正常運作不過，廠商也必須導入 API 來提供這項服務的營利方式

package android.frameworks.automotive.display@1.0;

import android.hardware.graphics.bufferqueue@2.0::IGraphicBufferProducer;

interface IAutomotiveDisplayProxyService {
    /**
     * Gets an IGraphicBufferProducer instance from the service.
     *
     * @param  id   Target's stable display identifier
     *
     * @return igbp Returns an IGraphicBufferProducer object, that can be
     *              converted to an ANativeWindow object.
     */
    getIGraphicBufferProducer(uint64_t id) generates (IGraphicBufferProducer igbp);

    /**
     * Sets the ANativeWindow, which is associated with the
     * IGraphicBufferProducer, to be visible and to take over the display.
     *
     * @param  id      Target display ID
     *
     * @return success Returns true on success.
     */
    showWindow(uint64_t id) generates (bool success);

    /**
     * Sets the ANativeWindow, which is associated with the
     * IGraphicBufferProducer, to be invisible and to release the control
     * over display.
     *
     * @param  id      Target display ID
     *
     * @return success Returns true on success.
     */
    hideWindow(uint64_t id) generates (bool success);

    /**
     * Returns the stable identifiers of all available displays.
     *
     * @return ids A list of stable display identifiers.
     */
    getDisplayIdList() generates (vec<uint64_t> ids);

    /**
     * Returns the descriptor of the target display.
     *
     * @param  id    Stable ID of a target display.
     * @return cfg   DisplayConfig of the active display.
     * @return state Current state of the active display.
     */
    getDisplayInfo(uint64_t id) generates (HwDisplayConfig cfg, HwDisplayState state);
}

若要使用這項服務：

取得 IAutomotiveDisplayProxyService。

android::sp<IAutomotiveDisplayProxyService> windowProxyService =
    IAutomotiveDisplayProxyService::getService("default");
if (windowProxyService == nullptr) {
    LOG(ERROR) << "Cannot use AutomotiveDisplayProxyService. Exiting.";
    return 1;
}

從服務擷取有效顯示資訊，以判斷解析度。

// We use the first display in the list as the primary.
pWindowProxy->getDisplayInfo(displayId, [this](auto dpyConfig, auto dpyState) {
    DisplayConfig *pConfig = (DisplayConfig*)dpyConfig.data();
    mWidth = pConfig->resolution.getWidth();
    mHeight = pConfig->resolution.getHeight();

    ui::DisplayState* pState = (ui::DisplayState*)dpyState.data();
    if (pState->orientation != ui::ROTATION_0 &&
        pState->orientation != ui::ROTATION_180) {
        // rotate
        std::swap(mWidth, mHeight);
    }

    LOG(DEBUG) << "Display resolution is " << mWidth << " x " << mHeight;
});

擷取硬體 IGraphicBufferProducer (或者來自 IAutomotiveDisplayProxyService 的 HIDL GraphicBufferProducer (HGBP)：

mGfxBufferProducer = pWindowProxy->getIGraphicBufferProducer(displayId);
if (mGfxBufferProducer == nullptr) {
    LOG(ERROR) << "Failed to get IGraphicBufferProducer from "
               << "IAutomotiveDisplayProxyService.";
    return false;
}

使用 API 從擷取的 HGBP 取得 SurfaceHolder libbufferqueueconverter:

mSurfaceHolder = getSurfaceFromHGBP(mGfxBufferProducer);
if (mSurfaceHolder == nullptr) {
    LOG(ERROR) << "Failed to get a Surface from HGBP.";
    return false;
}

使用SurfaceHolder API libbufferqueueconverter：

mWindow = getNativeWindow(mSurfaceHolder.get());
if (mWindow == nullptr) {
    LOG(ERROR) << "Failed to get a native window from Surface.";
    return false;
}

使用原生視窗建立 EGL 視窗介面，然後算繪：

// Set up our OpenGL ES context associated with the default display
mDisplay = eglGetDisplay(EGL_DEFAULT_DISPLAY);
if (mDisplay == EGL_NO_DISPLAY) {
    LOG(ERROR) << "Failed to get egl display";
    return false;
}
...

// Create the EGL render target surface
mSurface = eglCreateWindowSurface(mDisplay, egl_config, mWindow, nullptr);
if (mSurface == EGL_NO_SURFACE) {
    LOG(ERROR) << "eglCreateWindowSurface failed.";
    return false;
}
...

撥打電話給「IAutomotiveDisplayProxyService::showWindow()」：在螢幕上顯示轉譯後的檢視畫面這項服務的優先順序最高，因此，請一律由目前的擁有者控管螢幕：
```
mAutomotiveDisplayProxyService->showWindow();
```

請參閱《service.cpp》和《GlWrapper.cpp》在$ANDROID_BUILD_TOP/packages/services/Car/evs/sampleDriver/搜尋更多實作詳細資料

EVS HAL 實作需要在粗體。

cc_binary {
    name: "android.hardware.automotive.evs@1.1-sample",

    vendor: true,

    srcs: [
        ...
    ],

    shared_libs: [
        ...
        "libbufferqueueconverter",
        "android.hidl.token@1.0-utils",
        "android.frameworks.automotive.display@1.0",
        "android.hardware.graphics.bufferqueue@1.0",
        "android.hardware.graphics.bufferqueue@2.0",
    ],

多螢幕支援

顯示裝置列舉及擷取顯示資訊

EVS 架構與相機裝置列舉一樣，提供了列舉可用的螢幕。靜態顯示 ID 對類型為類型 ID 編碼以小寫位元組和 Extended Display IDentification Data 表示。 IAutomotiveDisplayProxyService::getDisplayIdList() 會傳回清單實體本地螢幕的顯示 ID，這類螢幕適用於 EVS 服務且 IEvsEnumerator::getDisplayIdList() 會傳回顯示內容清單偵測到的螢幕已連線清單中第一個 ID 一律為主螢幕。

interface IEvsEnumerator extends @1.0::IEvsEnumerator {
    ...
    /**
     * Returns a list of all EVS displays available to the system
     *
     * @return displayIds Identifiers of available displays.
     */
    getDisplayIdList() generates (vec<uint8_t> displayIds);
};

開啟目標顯示裝置

EVS 應用程式利用目標螢幕呼叫 IEvsEnumerator::openDisplay_1_1() 通訊埠編號：

android::sp<IEvsDisplay> pDisplay = pEvs->openDisplay_1_1(displayId);
if (pDisplay.get() == nullptr) {
    LOG(ERROR) << "EVS Display unavailable. Exiting.";
    return 1;
}

注意：一次只能使用一部螢幕，這代表目前的 EVS 用戶端在另一個 EVS 用戶端時遺失顯示內容要求開啟螢幕。