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13# car-evs-helper-lib
14This directory contains two modules that are used by other apps to process
15CarEvsBufferDescriptor and render its contents to the display with EGL.
16* `car-evs-helper-lib:` This library contains `CarEvsGLSurfaceView` and
17  `CarEvsBufferRenderer` classes.
18* `libcarevsglrenderer_jni`: This is a JNI library `CarEvsBufferRenderer` uses
19  to render the contents of `CarEvsBufferDescriptor` with EGL.
20## How to use
21Please follow below instructions to delegate a `CarEvsBufferDescriptor` rendering
22to this library.  A reference implementation is also available at
23`packages/services/Car/tests/CarEvsCameraPreviewApp`.
241. Make the application refer to `car-evs-helper-lib` and
25   `libcarevsglrenderer_jni` libraries by adding below lines to `Android.bp`.
26```
27static_libs: ["car-evs-helper-lib"],
28jni_libs: ["libcarevsglrenderer_jni"],
29```
302. Implement `CarEvsGLSurfaceView.Callback` interface. For example,
31```
32/**
33 * This method is called by the renderer to fetch a new frame to draw.
34 */
35@Override
36public CarEvsBufferDescriptor getNewFrame() {
37    synchronized(mLock) {
38        // Return a buffer to render.
39        return mBufferToRender;
40    }
41}
42/**
43 * This method is called by the renderer when it is done with a passed
44 * CarEvsBufferDescriptor object.
45 */
46@Override
47public void returnBuffer(CarEvsBufferDescriptor buffer) {
48    // Return a buffer to CarEvsService.
49    try {
50        mEvsManager.returnFrameBuffer(buffer);
51    } catch (Exception e) {
52        ...
53    }
54    ...
55}
56```
573. Create `CarEvsGLSurfaceView` with the application context,
58   `CarEvsGLSurfaceView.Callback` object, and, optionally, a desired in-plane
59   rotation angle.
60```
61private CarEvsGLSurfaceView mView;
62@Override
63protected void onCreate(Bundle savedInstanceState) {
64    ...
65    mView = CarEvsGLSurfaceView(getAppliation(), this, /* angleInDegree= */ 0);
66    ...
67}
68```
694. Start a video stream and update wheneven new frame buffer arrives.  For
70   example,
71```
72private final CarEvsManager.CarEvsStreamCallback mStreamHandler =
73    new CarEvsManager.CarEvsStreamCallback() {
74    ...
75    @Override
76    public void onNewFrame(CarEvsBufferDescriptor buffer) {
77      synchronized(mLock) {
78        mBufferToRender = buffer;
79      }
80    }
81}
82```
83