Google Glass Camera: setPreviewCallback

Question

I have an operating android app that utilizes preview callbacks, to process the image after every frame from the preview (the preview is paused for a minute while the calculations take place). It works great! But, now I am trying to get Google Glass to do the same thing: activate Preview, activate preview callback, activating the calculations.

This issue likely has to do with how Camera is defined: Camera mCamera = null;

but, I cannot define it as Camera.open(); with Google Glass because it fails. Thus when i get to defining the callback, I'm told it may produce a NullPointerException, and indeed I get the following error string:

Process: com.ead.glasscam.app, PID: 14231 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.ead.glasscam.app/com.ead.glasscam.app.MainActivity}: java.lang.NullPointerException at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2235) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2285) at android.app.ActivityThread.access$800(ActivityThread.java:138) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1236) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:149) at android.app.ActivityThread.main(ActivityThread.java:5061) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:515) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:794) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:610) at dalvik.system.NativeStart.main(Native Method) Caused by: java.lang.NullPointerException at com.ead.glasscam.app.MainActivity.onCreate(MainActivity.java:100) at android.app.Activity.performCreate(Activity.java:5236) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1089) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2199) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2285) at android.app.ActivityThread.access$800(ActivityThread.java:138) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1236) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:149) at android.app.ActivityThread.main(ActivityThread.java:5061) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:515) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:794) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:610) at dalvik.system.NativeStart.main(Native Method)

So, the code:

// Attach a callback for preview
mPreviewCallback camCallback = new mPreviewCallback();
mCamera.setPreviewCallback(camCallback);

What is mPreviewCallback?:

public class mPreviewCallback implements Camera.PreviewCallback {

    public void onPreviewFrame(byte[] data, final Camera camera){
        Log.i("CAMERA", "Triggered Preview Frame");
    }
}

I really don't understand how to do this simple process on Android, with Google Glass. Thank you for reading.

Camera.open() can work in Glass. Obvious question, but have you included camera permissions in your manifest.xml? — Nathaniel Wendt, Jun 05 '14 at 18:02

Johnny505 · Answer 1 · 2014-06-09T11:32:51.720

Checkout this example from jaredsburrows, it uses the camera preview on Glass and I used it in a project once (It Works! ;) )

https://github.com/jaredsburrows/OpenQuartz/tree/master/example-apps/OG_CameraApp

public class CameraView extends SurfaceView implements SurfaceHolder.Callback
{
    private SurfaceHolder surfaceHolder = null;
    private Camera camera = null;

    @SuppressWarnings("deprecation")
    public CameraView(Context context) 
    {
        super(context);

        surfaceHolder = this.getHolder();
        surfaceHolder.addCallback(this);
        surfaceHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
    }

    /*
     * (non-Javadoc)
     * @see android.view.SurfaceHolder.Callback#surfaceCreated(android.view.SurfaceHolder)
     */
    @Override
    public void surfaceCreated(SurfaceHolder holder) 
    {
        camera = Camera.open();

        // Set the Hotfix for Google Glass
        this.setCameraParameters(camera);

        // Show the Camera display
        try 
        {
            camera.setPreviewDisplay(holder);
        } 
        catch (Exception e) 
        {
            this.releaseCamera();
        }
    }

    /*
     * (non-Javadoc)
     * @see android.view.SurfaceHolder.Callback#surfaceChanged(android.view.SurfaceHolder, int, int, int)
     */
    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) 
    {
        // Start the preview for surfaceChanged
        if (camera != null)
        {
            camera.startPreview();
        }
    }

    /*
     * (non-Javadoc)
     * @see android.view.SurfaceHolder.Callback#surfaceDestroyed(android.view.SurfaceHolder)
     */
    @Override
    public void surfaceDestroyed(SurfaceHolder holder) 
    {
        // Do not hold the camera during surfaceDestroyed - view should be gone
        this.releaseCamera();
    }

    /**
     * Important HotFix for Google Glass (post-XE11) update
     * @param camera Object
     */
    public void setCameraParameters(Camera camera)
    {
        if (camera != null)
        {
            Parameters parameters = camera.getParameters();
            parameters.setPreviewFpsRange(30000, 30000);
            camera.setParameters(parameters);   
        }
    }

    /**
     * Release the camera from use
     */
    public void releaseCamera() 
    {
        if (camera != null) 
        {
            camera.release();
            camera = null;
        }
    }
}

Google Glass Camera: setPreviewCallback

1 Answers1