public void startScroll(int startX, int startY, int dx, int dy, int duration) {
        mMode = SCROLL_MODE;
        mFinished = false;
        mDuration = duration;
        mStartTime = AnimationUtils.currentAnimationTimeMillis();
        mStartX = startX;
        mStartY = startY;
        mFinalX = startX + dx;
        mFinalY = startY + dy;
        mDeltaX = dx;
        mDeltaY = dy;
        mDurationReciprocal = 1.0f / (float) mDuration;
    }
Start scrolling by providing a starting point and the distance to travel.

@param startX Starting horizontal scroll offset in pixels. Positive
       numbers will scroll the content to the left.
@param startY Starting vertical scroll offset in pixels. Positive numbers
       will scroll the content up.
@param dx Horizontal distance to travel. Positive numbers will scroll the
       content to the left.
@param dy Vertical distance to travel. Positive numbers will scroll the
       content up.
@param duration Duration of the scroll in milliseconds.
menudrawer/src/net/simonvt/menudrawer/Scroller.java