Cannot scale or flip surfaceview matrix

Question

I am making a camera application. I use a SurfaceView to display my camera preview.

        preview=(SurfaceView)findViewById(R.id.preview);
        previewHolder=preview.getHolder();
        previewHolder.addCallback(surfaceCallback);
        previewHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
        Matrix m = preview.getMatrix();
         m.setScale(-1,1);

What I'm trying to do is to flip the SurfaceView matrix. I tried to use preScale() and postScale(), and I tried to add the last 2 lines to to Surfaceview.callback method like this:

   public void surfaceChanged(SurfaceHolder holder, int format,
                                   int width, int height) {                     
          initPreview(width, height);
          startPreview();
Matrix m = preview.getMatrix();
         m.setScale(-1,1);
                  }

but I get the same error everywhere (along with app crashing):

java.lang.IllegalStateException: Matrix can not be modified

What am I doing wrong? Is it possible to change scale off SurfaceView whatsoever? If not, is there some other way to flip camera preview?

Answer 1

To clarify the answer posted by Madhusudan a few months ago, instead of creating a blank Matrix and then setting it equal to your previews Matrix, you have to do a deep copy of the Matrix using set().

It would look something like this:

Matrix m = new Matrix(preview.getMatrix());
m.postRotate(90.0f);
canvas.drawBitmap(bitmap, m, NULL);

Or something like this:

Matrix m = new Matrix();
m.set(preview.getMatrix());
m.postRotate(90.0f);
canvas.drawBitmap(bitmap, m, NULL);