ZoomOutPageTransformer.java

package com.example.animation;

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;


	@Override
	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)
		{
			// [-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);
		}
	}
}