Android实现图片的倒影效果

  
import android.app.Activity;  
import android.graphics.Bitmap;  
import android.graphics.BitmapFactory;  
import android.graphics.Canvas;  
import android.graphics.LinearGradient;  
import android.graphics.Matrix;  
import android.graphics.Paint;  
import android.graphics.PorterDuff;  
import android.graphics.PorterDuffXfermode;  
import android.graphics.Shader;  
import android.graphics.drawable.BitmapDrawable;  
import android.os.Bundle;  
import android.widget.ImageView;  
  
public class MainActivity extends Activity {  
    private ImageView mRevertImageView;  
    private Bitmap mSourceBitmap;  //原图  
    private Bitmap mRevertBitmap;  //倒立图  
  
    @Override  
    protected void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  
        setContentView(R.layout.activity_main);  
  
        mRevertImageView = (ImageView)findViewById(R.id.im_revert);  
        mSourceBitmap = BitmapFactory.decodeResource(getResources(),R.drawable.source);  
        mRevertImageView.setBackground(new BitmapDrawable(getResources(),revertBitmap()));  
    }  
  
    private Bitmap revertBitmap() {  
        //1.倒立图  
        Matrix matrix = new Matrix();  
        matrix.preScale(1,-1);   //以X轴向下翻转  
        int width = mSourceBitmap.getWidth();  
        int height = mSourceBitmap.getHeight();  
  
        //生成倒立图，宽度和原图一致，高度为原图的一半  
        mRevertBitmap = Bitmap.createBitmap(mSourceBitmap,height / 2,width,matrix,false);  
  
        //2.要生成原图加上倒立图，先生成一个可变空的Bitmap,高度为原图高度的1.5倍（包括原图和倒立图的高度）  
        int gap = 10; //间隙空白  
        Bitmap bitmap = Bitmap.createBitmap(width,height + height / 2,Bitmap.Config.ARGB_8888);  
        Paint paint = new Paint();  
        Canvas canvas = new Canvas(bitmap);  
        canvas.drawBitmap(mSourceBitmap,paint);  //绘制原图  
        canvas.drawBitmap(mRevertBitmap,height + gap,paint);  //绘制倒立图  
  
        //3.画笔使用LinearGradient 线性渐变渲染  
        LinearGradient lg = new LinearGradient(0,bitmap.getHeight(),0xabff0000,0x00ffff00,Shader.TileMode.MIRROR);  
        paint.setShader(lg);  
  
        //4.指定画笔的Xfermode 即绘制的模式（不同的模式，绘制的区域不同）  
        paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_ATOP));  
  
        //5.在倒立图区，绘制矩形渲染图层  
        canvas.drawRect(0,paint);  
        paint.setXfermode(null);  
        return bitmap;  
    }  
  
    //缩放图片  
    private Bitmap resizeImage(Bitmap bitmap,int width,int height) {  
        int originWidth = bitmap.getWidth();  
        int originHeight = bitmap.getHeight();  
  
        float scaleWidth = width / originWidth;  
        float scaleHeight = height / originHeight;  
  
        Matrix matrix = new Matrix();  
        matrix.postScale(scaleWidth,scaleHeight);  
        Bitmap resizeBitmap = Bitmap.createBitmap(bitmap,originWidth,originHeight,true);  
        return resizeBitmap;  
    }  
}  

PorterDuffXfermode 定义的模式如下：
private static final Xfermode[] sModes = {
?new PorterDuffXfermode(PorterDuff.Mode.CLEAR),? ? //所绘制不会提交到画布上
?new PorterDuffXfermode(PorterDuff.Mode.SRC),? ? ? //显示上层绘制图片
?new PorterDuffXfermode(PorterDuff.Mode.DST),? ? ?//显示下层绘制图片
?new PorterDuffXfermode(PorterDuff.Mode.SRC_OVER),//正常绘制显示，上下层绘制叠盖
?new PorterDuffXfermode(PorterDuff.Mode.DST_OVER),//上下层都显示。下层居上显示
?new PorterDuffXfermode(PorterDuff.Mode.SRC_IN),? //取两层绘制交集。显示上层
?new PorterDuffXfermode(PorterDuff.Mode.DST_IN),? //取两层绘制交集。显示下层
?new PorterDuffXfermode(PorterDuff.Mode.SRC_OUT),?//取上层绘制非交集部分
?new PorterDuffXfermode(PorterDuff.Mode.DST_OUT),?//取下层绘制非交集部分
?new PorterDuffXfermode(PorterDuff.Mode.SRC_ATOP),//取下层非交集部分与上层交集部分
?new PorterDuffXfermode(PorterDuff.Mode.DST_ATOP),//取上层非交集部分与下层交集部分
?new PorterDuffXfermode(PorterDuff.Mode.XOR),? ? ?//滤色效果
?new PorterDuffXfermode(PorterDuff.Mode.DARKEN),? //滤色效果
?new PorterDuffXfermode(PorterDuff.Mode.LIGHTEN),?//滤色效果
?new PorterDuffXfermode(PorterDuff.Mode.MULTIPLY),//滤色效果
?new PorterDuffXfermode(PorterDuff.Mode.SCREEN) ? ?//滤色效果
};