CameraSource.java 文件源码

/**
 * Creates one buffer for the camera preview callback.  The size of the buffer is based off of
 * the camera preview size and the format of the camera image.
 *
 * @return a new preview buffer of the appropriate size for the current camera settings
 */
private byte[] createPreviewBuffer(Size previewSize) {
    int bitsPerPixel = ImageFormat.getBitsPerPixel(ImageFormat.NV21);
    long sizeInBits = previewSize.getHeight() * previewSize.getWidth() * bitsPerPixel;
    int bufferSize = (int) Math.ceil(sizeInBits / 8.0d) + 1;

    //
    // NOTICE: This code only works when using play services v. 8.1 or higher.
    //

    // Creating the byte array this way and wrapping it, as opposed to using .allocate(),
    // should guarantee that there will be an array to work with.
    byte[] byteArray = new byte[bufferSize];
    ByteBuffer buffer = ByteBuffer.wrap(byteArray);
    if (!buffer.hasArray() || (buffer.array() != byteArray)) {
        // I don't think that this will ever happen.  But if it does, then we wouldn't be
        // passing the preview content to the underlying detector later.
        throw new IllegalStateException("Failed to create valid buffer for camera source.");
    }

    mBytesToByteBuffer.put(byteArray, buffer);
    return byteArray;
}