ZoomOutPageTransformer

    private static final float MIN_SCALE = 0.9f;
    private static final float MIN_ALPHA = 0.8f;

    private static float defaultScale = 0.9f;

    public void transformPage(View view, float position) {
        //获取屏幕宽度
        int pageWidth = view.getWidth();
        //获取屏幕高度
        int pageHeight = view.getHeight();

        if (position < -1) { // [-Infinity,-1)
            // This page is way off-screen to the left.
            view.setAlpha(0);
            view.setScaleX(defaultScale);
            view.setScaleY(defaultScale);
        } else if (position <= 1) { // [-1,1]
            // Modify the default slide transition to shrink the page as well
            float scaleFactor = Math.max(MIN_SCALE, 1 - Math.abs(position));
            float vertMargin = pageHeight * (1 - scaleFactor) / 2;
            float horzMargin = pageWidth * (1 - scaleFactor) / 2;
            if (position < 0) {
            //viewpager左边item的显示
                view.setTranslationX(horzMargin - vertMargin / 2);
                view.setTranslationY(vertMargin);
            } else {
             //viewpager右边item的显示
                view.setTranslationX(-horzMargin + vertMargin / 2);
            //设置Y轴的位置
                view.setTranslationY(vertMargin);
            }

            // Scale the page down (between MIN_SCALE and 1)

            view.setScaleX(scaleFactor);
            view.setScaleY(scaleFactor);
            // Fade the page relative to its size.
            view.setAlpha(MIN_ALPHA +
                    (scaleFactor - MIN_SCALE) /
                            (1 - MIN_SCALE) * (1 - MIN_ALPHA));

        } else { // (1,+Infinity]
            // This page is way off-screen to the right.
            view.setAlpha(0);
            view.setScaleX(defaultScale);
            view.setScaleY(defaultScale);
        }
    }