canvas drawBitmap doesnot display camera preview

Question

I am not able to display the camera preview on my android screen using the canvas.drawbitmap. The screen is all black, I verified the drawtext method is working. Please let me know what I am doing wrong !!

class CameraView extends SurfaceView implements
            SurfaceHolder.Callback, Camera.PreviewCallback {
static {
    System.loadLibrary("canvasdraw");
}

public native void decode(Bitmap pTarget, byte[] pSource);

private Camera mCamera;
private byte[] mVideoSource;
private Bitmap mBackBuffer;
private Paint mPaint;

public CameraView(Context context) {
    super(context);

    // Registers current class so that it listens to surface
    // event (creation, destruction and changes).
    getHolder().addCallback(this);
    // Clears the flag keeping the surface from getting drawn.
    // Necessary when not drawing from a thread.
    setWillNotDraw(false);
}

public void surfaceCreated(SurfaceHolder holder) {
    try {
        // Acquires the default camera.
       // mCamera = Camera.open();

        try {
            mCamera = Camera.open(0);
        } catch (RuntimeException e) {
            Log.e("CameraTest", "Camera Open filed");
            return;
        }
        // Sets landscape mode to avoid complications related to
        // screen orientation handling.
        mCamera.setDisplayOrientation(0);
        // Registers callbacks. Automatic preview is deactivated
        // as we want to process data ourself (in a buffer).
        mCamera.setPreviewDisplay(null);
        mCamera.setPreviewCallbackWithBuffer(this);
    } catch (IOException eIOException) {
        mCamera.release();
        mCamera = null;
        throw new IllegalStateException();
    }
}

public void surfaceChanged(SurfaceHolder pHolder, int pFormat,
                int pWidth, int pHeight) {
    mCamera.stopPreview();

    // Finds a suitable resolution.
    Size lSize = findBestResolution(pWidth, pHeight);

    // Prepares video source and back buffers.
    PixelFormat lPixelFormat = new PixelFormat();
    PixelFormat.getPixelFormatInfo(mCamera.getParameters()
                    .getPreviewFormat(), lPixelFormat);
    int lSourceSize = lSize.width * lSize.height
                    * lPixelFormat.bitsPerPixel / 8;
    mVideoSource = new byte[lSourceSize];
    mBackBuffer = Bitmap.createBitmap(lSize.width, lSize.height,
                    Bitmap.Config.ARGB_8888);

    // Set-up camera size and video format. YCbCr_420_SP
    // should be the default on Android anyway.
    Camera.Parameters lParameters = mCamera.getParameters();
    lParameters.setPreviewSize(lSize.width, lSize.height);
    lParameters.setPreviewFormat(PixelFormat.YCbCr_420_SP);
    mCamera.setParameters(lParameters);

    // Starts receiving pictures from the camera.
    mCamera.addCallbackBuffer(mVideoSource);
    mCamera.startPreview();
}

private Size findBestResolution(int pWidth, int pHeight) {
    List<Size> lSizes = mCamera.getParameters()
                    .getSupportedPreviewSizes();
    // Finds the biggest resolution which fits the screen.
    // Else, returns the first resolution found.
    Size lSelectedSize = mCamera.new Size(0, 0);
    for (Size lSize : lSizes) {
        if ((lSize.width <= pWidth)
                        && (lSize.height <= pHeight)
                        && (lSize.width >= lSelectedSize.width)
                        && (lSize.height >= lSelectedSize.height)) {
            lSelectedSize = lSize;
        }
    }
    // Previous code assume that there is a preview size smaller
    // than screen size. If not, hopefully the Android API
    // guarantees that at least one preview size is available.
    if ((lSelectedSize.width == 0)
                    || (lSelectedSize.height == 0)) {
        lSelectedSize = lSizes.get(0);
    }
    return lSelectedSize;
}

public void surfaceDestroyed(SurfaceHolder holder) {
    // Releases camera which is a shared resource.
    if (mCamera != null) {
        mCamera.stopPreview();
        mCamera.release();
        // These variables can take a lot of memory. Gets rid of
        // them as fast as we can.
        mCamera = null;
        mVideoSource = null;
        mBackBuffer = null;
    }
}

public void onPreviewFrame(byte[] pData, Camera pCamera) {
    // New data has been received from camera. Processes it and
    // requests surface to be redrawn right after.
    decode(mBackBuffer, pData);
    invalidate();
}

@Override
protected void onDraw(Canvas pCanvas) {
    if (mCamera != null) {

      //  Paint textPaint = new Paint();
     //   textPaint.setARGB(255, 200, 0, 0);
     //   textPaint.setTextSize(60);

    //    pCanvas.drawText("Hello World!", 50, 50, textPaint);

     // Draws resulting image at screen origin.
        pCanvas.drawBitmap(mBackBuffer, 0, 0, null);
        // Enqueues buffer again to get next image.
        mCamera.addCallbackBuffer(mVideoSource);
    }
}
}

Answer 1

When you set preview display to null, or give it a fake surface, camera preview will not work. On some devices the system may have bugs, and using sneaky workarounds it is possible to start preview frames acquisition without displaying preview on the screen.

But maybe for your purposes, setPreviewTexture() will do the job.