private float interpolate() {
            float t = 1f * (System.currentTimeMillis() - mStartTime) / mZoomDuration;
            t = Math.min(1f, t);
            t = mInterpolator.getInterpolation(t);
            return t;
        }
Calculate Matrix for FIT_CENTER

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