@Override
        public void run() {

            float t = interpolate();
            float scale = mZoomStart + t * (mZoomEnd - mZoomStart);
            float deltaScale = scale / getScale();

            onGestureListener.onScale(deltaScale, mFocalX, mFocalY);

            // We haven't hit our target scale yet, so post ourselves again
            if (t < 1f) {
                Compat.postOnAnimation(mImageView, this);
            }
        }
Calculate Matrix for FIT_CENTER

@param drawable - Drawable being displayed
main/src/main/java/com/quxianggif/common/view/photoview/PhotoViewAttacher.java