Android 颜色渲染(七) RadialGradient 环形渲染实现水波纹效果

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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;
    }

}