ParallaxTransformer.java

package com.cinemagraph;

import android.graphics.Matrix;
import android.support.v4.view.ViewPager;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.FrameLayout;
import android.widget.ImageView;
import android.widget.RelativeLayout;

/**
 * 
 * @author brendanw
 *  * Reminders about position:
 * (1) When a page fills the screen its position is 0
 * (2) When a page is drawn off the right side of the screen, its position is 1
 * (3) When a page is drawn off the left side of the screen, its position is -1
 */
public class ParallaxTransformer implements ViewPager.PageTransformer {
	
	private static final String TAG = ParallaxTransformer.class.getSimpleName();
	
	@Override
	public void transformPage(View view, float position) {

		RelativeLayout root = (RelativeLayout) ((FrameLayout) view)
				.getChildAt(0);
		Button previewBtn = (Button) root.findViewById(R.id.preview_btn);
		Button wallpaperBtn = (Button) root.findViewById(R.id.set_wallpaper_btn);
		previewBtn.setAlpha(1.0f - (float)Math.sqrt(Math.abs(position)));
		wallpaperBtn.setAlpha(1.0f - (float)Math.sqrt(Math.abs(position)));
		
		ImageView imageView = (ImageView) root.getChildAt(0);

		if (position < -1) {
		} else if (position <= 1) {

			Matrix matrix = new Matrix();
			matrix.reset();

			float viewWidth = imageView.getWidth();
			float viewHeight = imageView.getHeight();

			float intrinsicWidth = imageView.getDrawable().getIntrinsicWidth();
			float intrinsicHeight = imageView.getDrawable().getIntrinsicHeight();

			float newWidth = viewWidth;
			float newHeight = viewHeight;

			float scale = 0.0f;

			/*
			 * if the difference in width is proportionally greater than difference in
			 * height (ex: 2.5 > 1.9) then scale the bitmap by the height factor
			 */
			if (intrinsicWidth / viewWidth > intrinsicHeight / viewHeight) {
				scale = viewHeight / intrinsicHeight;
				matrix.setScale(scale, scale);
				newWidth = intrinsicWidth * scale;
			}
			/*
			 * else, scale the bitmap by the width factor
			 */
			else {
				scale = viewWidth / intrinsicWidth;
				matrix.setScale(scale, scale);
				newHeight = intrinsicHeight * scale;
			}

			/* offset to center the view horizontally */
			float xOffset = (viewWidth - newWidth) / 2;

			/*
			 * strategy: 
			 * 1) get pixels moved relative to the view frame (X) 
			 * 2) move the bitmap 0.5f * X
			 */
			float xPos = -position * viewWidth * 0.5f + xOffset;

			// IGNORE BELOW THIS LINE
			float yPos = (viewHeight - newHeight) / 2;
			matrix.postTranslate(xPos, yPos);
			imageView.setScaleType(ImageView.ScaleType.MATRIX);
			imageView.setImageMatrix(matrix);
		} else {
		}
	}
}