在相机预览中没有使用setAlpha

Question

I want to create camera preview working on top of the Android system. I also want to make it transparent in 50%. And here is the problem. setAlpha does not work for me when i use it.

This is my service, which i use to add SurfaceView to window:

WindowManager.LayoutParams tmp = new WindowManager.LayoutParams(
            measuredWidth,measuredHeight,
            WindowManager.LayoutParams.TYPE_SYSTEM_OVERLAY,
            WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
                    | WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL
                    | WindowManager.LayoutParams.FLAG_WATCH_OUTSIDE_TOUCH
                    | WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE
                    | WindowManager.LayoutParams.FLAG_LAYOUT_NO_LIMITS,
            PixelFormat.TRANSPARENT);
    /*s.setZOrderOnTop(true);
    s.setAlpha(0.5f);
    tmp.alpha=0.0f;

    wm.addView(s, tmp);*/

    LayoutInflater layoutInflater = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    View mCameraView = layoutInflater.inflate(R.layout.camera_surface, null);
    StunGunPreview preview=(StunGunPreview) mCameraView.findViewById(R.id.textureView);
    wm.addView(mCameraView, tmp);



public class StunGunPreview extends SurfaceView implements
        SurfaceHolder.Callback {
    SurfaceHolder holder;
    static Camera mCamera;
    Context c;
    WindowManager wm;

    public StunGunPreview(Context context, AttributeSet attrs) {
        super(context,attrs);
        c = context;
        wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);

        holder = this.getHolder();
        holder.addCallback(this);
        holder.setFormat(PixelFormat.TRANSPARENT);
       setZOrderOnTop(true);
    }

    @Override
    public void surfaceCreated(SurfaceHolder holder) {

        start_camera();
    }

    private void start_camera() {
        try {
            mCamera = Camera.open();
        } catch (RuntimeException e) {
            return;
        }
        try {
            mCamera.setPreviewDisplay(holder);
            mCamera.startPreview();
        } catch (Exception e) {
            return;
        }
    }
}

Answer 1

A SurfaceView has two parts, the Surface and the View. Calling the View's setAlpha() method will only affect content drawn on the View, which doesn't help you, because the Camera frames are being sent to the Surface.

The Surface is an independent layer. The current API doesn't provide a way to set a "plane alpha", so you just get whatever the pixel values have. For Camera and video output, the YUV-to-RGB conversion always generates fully opaque pixels.

To do what you want, you'd need to send the Camera preview to a SurfaceTexture, which converts the frame to an OpenGL ES "external" texture. You can then render that onto a partially-transparent quad. It's a fair bit of work, but once you have it working you can do just about anything with the live camera image (like wrap it around a sphere or send it bouncing around the screen).

A simple example of this can be found in the "texture from camera" Activity in Grafika .