code: public boolean computeZoom() {
          if (mFinished) {
              return false;
          }
  
          long tRTC = SystemClock.elapsedRealtime() - mStartRTC;
          if (tRTC >= mAnimationDurationMillis) {
              mFinished = true;
              mCurrentZoom = mEndZoom;
              return false;
          }
  
          float t = tRTC * 1f / mAnimationDurationMillis;
          mCurrentZoom = mEndZoom * mInterpolator.getInterpolation(t);
          return true;
      }
docs: Computes the current zoom level, returning true if the zoom is still active and false if the zoom has finished.
  
  @see android.widget.Scroller#computeScrollOffset()