package me.twmm.twdroid.views;

import android.support.v4.view.ViewPager;
import android.view.View;

public class ZoomOutPageTransformer implements ViewPager.PageTransformer {
    private static final float MIN_SCALE = 0.85f;
    private static final float MIN_ALPHA = 0.5f;

    public void transformPage(View view, float position) {
        int pageWidth = view.getWidth();
        int pageHeight = view.getHeight();

        if (position < -1) { // [-Infinity,-1)
            // This page is way off-screen to the left.  
            view.setAlpha(0);

        } else if (position <= 1) //a页滑动至b页 ； a页从 0.0 -1 ；b页从1 ~ 0.0  
        { // [-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) {
                view.setTranslationX(horzMargin - vertMargin / 2);
            } else {
                view.setTranslationX(-horzMargin + vertMargin / 2);
            }

            // 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);
        }
    }
}  
add zoomoutpageTransformer