java - Limits For Zooming Image

Question

I implemented multitouch zoom and drag for an image in a viewpager. How do I stop the image from passing a certain scale and x-position? I also want to know when the position is at the boundary I set. Here is my implementation of onTouch()

public boolean onTouch(View v, MotionEvent event) {
    // handle touch events here

    ImageView view = (ImageView) v;
    switch (event.getAction() & MotionEvent.ACTION_MASK) {
        case MotionEvent.ACTION_DOWN:
            savedMatrix.set(matrix);
            savedMatrix.
            start.set(event.getX(), event.getY());
            mode = DRAG;
            lastEvent = null;
            break;
        case MotionEvent.ACTION_POINTER_DOWN:
            oldDist = spacing(event);
            if (oldDist > 10f) {
                savedMatrix.set(matrix);
                midPoint(mid, event);
                mode = ZOOM;
            }
            lastEvent = new float[4];
            lastEvent[0] = event.getX(0);
            lastEvent[1] = event.getX(1);
            lastEvent[2] = event.getY(0);
            lastEvent[3] = event.getY(1);
            break;
        case MotionEvent.ACTION_UP:
        case MotionEvent.ACTION_POINTER_UP:
            mode = NONE;
            lastEvent = null;
            break;
        case MotionEvent.ACTION_MOVE:
            if (mode == DRAG) {
                matrix.set(savedMatrix);
                float dx = event.getX() - start.x;
                float dy = event.getY() - start.y;
                matrix.postTranslate(dx, dy);
            } else if (mode == ZOOM) {
                float newDist = spacing(event);
                if (newDist > 10f) {
                    matrix.set(savedMatrix);
                    float scale = (newDist / oldDist);
                    matrix.postScale(scale, scale, mid.x, mid.y);
                }
            }
            break;
    }

    view.setImageMatrix(matrix);
    return true;
}

So far I tried to store a total change of scale and movement, but it hasn't worked out so well. I'm hoping to find something that directly has to do with the Matrix methods