ZoomOutPageTransformer.java

package com.kedzie.vbox.app;

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

import com.nineoldandroids.view.ViewHelper;

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

    public void transformPage(View view, float position) {
        int pageWidth = view.getWidth();
        int pageHeight = view.getHeight();
        
        if (position < -1 || position > 1) { // [-ꝏ,-1) (1, +ꝏ)
            // This page is way off-screen to the left or right.
            ViewHelper.setAlpha(view, 0);
        } 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)
                ViewHelper.setTranslationX(view, horzMargin-vertMargin/2);
            else
                ViewHelper.setTranslationX(view, -horzMargin+vertMargin/2);
            // Scale the page down (between MIN_SCALE and 1)
            ViewHelper.setScaleX(view, scaleFactor);
            ViewHelper.setScaleY(view, scaleFactor);
            // Fade the page relative to its size.
            ViewHelper.setAlpha(view, MIN_ALPHA + (scaleFactor-MIN_SCALE) / (1-MIN_SCALE)*(1-MIN_ALPHA));
        } else { // (1,+Infinity]
            ViewHelper.setAlpha(view, 0);
        }
    }
}