利用环形渲染我们可以做到什么？ 其实很多都是非常常见的，比如上一篇实现的帮帮糖效果， 彩色的热气球,比如这里要讲到的水波纹效果，或者也可以理解为扩散色渲染效果

首先看一下效果图：

轻触屏幕，即可看到对应的效果，可以看到，实现这种效果，利用RadialGradient ,只需简单几行代码:

MainActivity:

package com.tony.testshader;

import android.os.Bundle;

import android.app.Activity;

import android.graphics.Bitmap;

import android.graphics.BitmapFactory;

import android.view.Menu;

import android.widget.SeekBar;

import android.widget.SeekBar.OnSeekBarChangeListener;

public class MainActivity extends Activity  implements OnSeekBarChangeListener{

     private WaterRipplesView waterRipplesView;

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        waterRipplesView = new WaterRipplesView(this);

        setContentView(waterRipplesView);

    }

    @Override

    public boolean onCreateOptionsMenu(Menu menu) {

        getMenuInflater().inflate(R.menu.main, menu);

        return true;

    }

}

WaterRipplesView:

package com.tony.testshader;

import android.content.Context;

import android.graphics.Bitmap;

import android.graphics.BitmapShader;

import android.graphics.Canvas;

import android.graphics.Color;

import android.graphics.Paint;

import android.graphics.RadialGradient;

import android.graphics.Shader;

import android.graphics.drawable.BitmapDrawable;

import android.graphics.drawable.ShapeDrawable;

import android.graphics.drawable.shapes.OvalShape;

import android.util.AttributeSet;

import android.util.DisplayMetrics;

import android.view.MotionEvent;

import android.view.View;

/**

 * 水波纹效果

 * @author tony

 *

 */

 public class WaterRipplesView extends View {

	Shader mBitmapShader = null;

	Bitmap mBitmapPn = null;

	Paint mPaint = null;

	Shader mRadialGradient = null;

	Canvas mCanvas = null;

	ShapeDrawable mShapeDrawable = null;

	public WaterRipplesView(Context context) {

		super(context);

		// 初始化工作

		Bitmap bitmapTemp = ((BitmapDrawable) getResources().getDrawable(

				R.drawable.leaf)).getBitmap();

		DisplayMetrics dm = getResources().getDisplayMetrics();

		// 创建与当前使用的设备窗口大小一致的图片

		mBitmapPn = Bitmap.createScaledBitmap(bitmapTemp, dm.widthPixels,

				dm.heightPixels, true);

		// 创建BitmapShader object

		mBitmapShader = new BitmapShader(mBitmapPn, Shader.TileMode.REPEAT,

				Shader.TileMode.MIRROR);

		mPaint = new Paint();

	}

	public WaterRipplesView(Context context, AttributeSet attrs) {

		super(context, attrs);

	}

	@Override

	protected void onDraw(Canvas canvas) {

		// TODO Auto-generated method stub

		super.onDraw(canvas);

		// 将图片裁剪为椭圆型

		// 创建ShapeDrawable object，并定义形状为椭圆

		mShapeDrawable = new ShapeDrawable(new OvalShape());// OvalShape:椭圆

		// 设置要绘制的椭圆形的东西为ShapeDrawable图片

		mShapeDrawable.getPaint().setShader(mBitmapShader);

		// 设置显示区域

		mShapeDrawable.setBounds(0, 0, mBitmapPn.getWidth(),

				mBitmapPn.getHeight());

		// 绘制ShapeDrawable

		mShapeDrawable.draw(canvas);

		if (mRadialGradient != null) {

			mPaint.setShader(mRadialGradient);

			canvas.drawCircle(0, 0, 1000, mPaint);

		}

	}

	// @覆写触摸屏事件

	public boolean onTouchEvent(MotionEvent event) {

		// @设置alpha通道（透明度）

		mPaint.setAlpha(400);

		mRadialGradient = new RadialGradient(event.getX(), event.getY(), 48,

				new int[] { Color.WHITE, Color.TRANSPARENT },null, Shader.TileMode.REPEAT);

		// @重绘

		postInvalidate();

		return true;

	}

}