Android 实现图片倒影效果

package org.yang.android.util.graphics;

import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.LinearGradient;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.PorterDuffXfermode;
import android.graphics.Bitmap.Config;
import android.graphics.PorterDuff.Mode;
import android.graphics.Shader.TileMode;

public class ReflectionImage
{
	public static int reflectionGap;

	public static int reflectImageHeight;

	public static Bitmap doReflection(Bitmap originalBitmap)
	{

		if (originalBitmap == null)
		{
			return null;
		}

		// 获取原图片的宽度和高度
		int width = originalBitmap.getWidth();
		int height = originalBitmap.getHeight();

		if (ReflectionImage.reflectImageHeight == 0)
		{
			ReflectionImage.reflectImageHeight = height / 3;
		}

		// 图片缩放，x轴变为原来的1倍，y轴为-1倍,实现图片的反转
		Matrix matrix = new Matrix();
		matrix.preScale(1, -1);

		// 创建反转后的图片Bitmap对象,高度为 ReflectionImage.reflectImageHeight
		Bitmap reflectionBitmap = Bitmap.createBitmap(originalBitmap, 0,
				ReflectionImage.reflectImageHeight, width,
				ReflectionImage.reflectImageHeight, matrix, false);

		// 创建标准的Bitmap对象，宽和原图一致,高度为（ 原图与倒影图的间距+倒影图的高度+原图的高度）
		Bitmap withReflectionBitmap = Bitmap
				.createBitmap(
						width,
						(height + ReflectionImage.reflectImageHeight + ReflectionImage.reflectionGap),
						Config.ARGB_8888);

		// 创建一个画面，以 withReflectionBitmap 为模板
		Canvas canvas = new Canvas(withReflectionBitmap);

		// 从上到下，先画原图
		canvas.drawBitmap(originalBitmap, 0, 0, null);

		// 因为 drawRect需要一个Paint画笔对象为参数，这里创建的是一个默认的Paint对象
		Paint defaultPaint = new Paint();

		// 再画间距
		canvas.drawRect(0, height, width, height
				+ ReflectionImage.reflectionGap, defaultPaint);

		// 最后画倒影图
		canvas.drawBitmap(reflectionBitmap, 0, height + reflectionGap, null);

		Paint paint = new Paint();

		// 这里用 LinearGradient 以实现倒影图的渐变效果
		LinearGradient shader = new LinearGradient(0,
				originalBitmap.getHeight(), 0,
				withReflectionBitmap.getHeight(), 0x70ffffff, 0x00ffffff,
				TileMode.MIRROR);
		paint.setShader(shader);
		paint.setXfermode(new PorterDuffXfermode(Mode.DST_IN));

		// 覆盖效果
		canvas.drawRect(0, height, width, withReflectionBitmap.getHeight(),
				paint);

		return withReflectionBitmap;
	}
}