自定义控件（7）---BlurMaskFilter边界阴影

Android中的很多自带控件都有类似软阴影的效果，比如说Button，使用BlurMaskFilter就可以得到类似的效果



activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#FFFFFF"
android:orientation="vertical" >

<com.aigestudio.customviewdemo.views.MaskFilterView
android:layout_width="match_parent"
android:layout_height="match_parent" />

</LinearLayout>

MeasureUtil

package com.aigestudio.customviewdemo.utils;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.Color;
import android.util.DisplayMetrics;

public final class MeasureUtil {
public static int[] getScreenSize(Activity activity) {
DisplayMetrics metrics = new DisplayMetrics();
activity.getWindowManager().getDefaultDisplay().getMetrics(metrics);
return new int[] { metrics.widthPixels, metrics.heightPixels };
}

}

MainActivity

package com.aigestudio.customviewdemo.activities;

import android.app.Activity;
import android.os.Bundle;

import com.aigestudio.customviewdemo.R;

public class MainActivity extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
}

MaskFilterView

package com.aigestudio.customviewdemo.views;

import android.app.Activity;
import android.content.Context;
import android.graphics.BlurMaskFilter;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;

import com.aigestudio.customviewdemo.utils.MeasureUtil;

public class MaskFilterView extends View {
private static final int RECT_SIZE = 800;
private Paint mPaint;// 画笔
private Context mContext;// 上下文环境引用

private int left, top, right, bottom;//

public MaskFilterView(Context context) {
this(context, null);
}

public MaskFilterView(Context context, AttributeSet attrs) {
super(context, attrs);
mContext = context;

// 初始化画笔
initPaint();

// 初始化资源
initRes(context);
/**
* 如果可以只针对某个View关闭硬件加速那岂不是很好么？当然，Android也给我们提供了这样的功能，我们可以在View中通过
*/
setLayerType(LAYER_TYPE_SOFTWARE, null);
}

/**
* 初始化画笔
*/
private void initPaint() {
// 实例化画笔
mPaint = new Paint(Paint.ANTI_ALIAS_FLAG | Paint.DITHER_FLAG);
mPaint.setStyle(Paint.Style.FILL);
mPaint.setColor(0xFF603811);

/**
* radius很容易理解，值越大我们的阴影越扩散
* SOLID，其效果就是在图像的Alpha边界外产生一层与Paint颜色一致的阴影效果而不影响图像本身
* NORMAL会将整个图像模糊掉
* OUTER会在Alpha边界外产生一层阴影且会将原本的图像变透明
* INNER则会在图像内部产生模糊
*/
mPaint.setMaskFilter(new BlurMaskFilter(20, BlurMaskFilter.Blur.SOLID));
}

/**
* 初始化资源
*/
private void initRes(Context context) {
/*
* 计算位图绘制时左上角的坐标使其位于屏幕中心
*/
left = MeasureUtil.getScreenSize((Activity) mContext)[0] / 2
- RECT_SIZE / 2;
top = MeasureUtil.getScreenSize((Activity) mContext)[1] / 2 - RECT_SIZE
/ 2;
right = MeasureUtil.getScreenSize((Activity) mContext)[0] / 2
+ RECT_SIZE / 2;
bottom = MeasureUtil.getScreenSize((Activity) mContext)[1] / 2
+ RECT_SIZE / 2;
}

@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
canvas.drawColor(Color.GRAY);

// 画一个矩形
//(float left, float top, float right, float bottom, Paint paint)
canvas.drawRect(left, top, right, bottom, mPaint);
}
}

或者下面的方法也可以实现

package com.aigestudio.customviewdemo.views;

import android.annotation.SuppressLint;
import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Paint.Style;
import android.util.AttributeSet;
import android.view.View;

import com.aigestudio.customviewdemo.utils.MeasureUtil;

@SuppressLint("NewApi")
public class ShadowView extends View {
private static final int RECT_SIZE = 800;// 方形大小
private Paint mPaint;// 画笔

private int left, top, right, bottom;// 绘制时坐标

public ShadowView(Context context, AttributeSet attrs) {
super(context, attrs);
// setShadowLayer不支持HW
setLayerType(LAYER_TYPE_SOFTWARE, null);

// 初始化画笔
initPaint();

// 初始化资源
initRes(context);
}

/**
* 初始化画笔
*/
private void initPaint() {
// 实例化画笔
mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
mPaint.setColor(Color.RED);
mPaint.setStyle(Style.FILL);
//radius表示阴影的扩散半径，而dx和dy表示阴影平面上的偏移值，shadowColor就不说了阴影颜色
mPaint.setShadowLayer(60, 3, 3, Color.DKGRAY);
}

/**
* 初始化资源
*/
private void initRes(Context context) {
/*
* 计算位图绘制时左上角的坐标使其位于屏幕中心
*/
left = MeasureUtil.getScreenSize((Activity) context)[0] / 2 - RECT_SIZE
/ 2;
top = MeasureUtil.getScreenSize((Activity) context)[1] / 2 - RECT_SIZE
/ 2;
right = MeasureUtil.getScreenSize((Activity) context)[0] / 2
+ RECT_SIZE / 2;
bottom = MeasureUtil.getScreenSize((Activity) context)[1] / 2
+ RECT_SIZE / 2;
}

@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);

// 先绘制位图
canvas.drawRect(left, top, right, bottom, mPaint);
}
}

如上所说BlurMaskFilter是根据Alpha通道的边界来计算模糊的，如果是一张图片（注：上面我们说过Android会把拷贝到资源目录的图片转为RGB565，具体原因具体分析我会单独开一篇帖子说，这里就先假设所有提及的图片格式为RGB565）你会发现没有任何效果，那么假使我们需要给图片加一个类似阴影的效果该如何做呢？其实很简单，我们可以尝试从Bitmap中获取其Alpha通道，并在绘制Bitmap前先以该Alpha通道绘制一个模糊效果不就行了？

如下面代码所示我们通过Bitmap的extractAlpha()方法从原图中分离出一个Alpha通道位图并在计算模糊滤镜的时候使用该位图生成模糊效果：



BlurMaskFilterView

package com.aigestudio.customviewdemo.views;

import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.BlurMaskFilter;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;

import com.aigestudio.customviewdemo.R;
import com.aigestudio.customviewdemo.utils.MeasureUtil;

public class BlurMaskFilterView extends View {
private Paint shadowPaint;// 画笔
private Context mContext;// 上下文环境引用
private Bitmap srcBitmap, shadowBitmap;// 位图和阴影位图

private int x, y;// 位图绘制时左上角的起点坐标

public BlurMaskFilterView(Context context) {
this(context, null);
}

public BlurMaskFilterView(Context context, AttributeSet attrs) {
super(context, attrs);
mContext = context;
// 记得设置模式为SOFTWARE
setLayerType(LAYER_TYPE_SOFTWARE, null);

// 初始化画笔
initPaint();

// 初始化资源
initRes(context);
}

/**
* 初始化画笔
*/
private void initPaint() {
// 实例化画笔
shadowPaint = new Paint(Paint.ANTI_ALIAS_FLAG | Paint.DITHER_FLAG);
shadowPaint.setColor(Color.DKGRAY);
//outer solid normal 都可以  但是inner不行
shadowPaint.setMaskFilter(new BlurMaskFilter(10, BlurMaskFilter.Blur.NORMAL));
}

/**
* 初始化资源
*/
private void initRes(Context context) {
// 获取位图
srcBitmap = BitmapFactory.decodeResource(context.getResources(), R.drawable.a);

// 获取位图的Alpha通道图
shadowBitmap = srcBitmap.extractAlpha();

/*
* 计算位图绘制时左上角的坐标使其位于屏幕中心
*/
x = MeasureUtil.getScreenSize((Activity) mContext)[0] / 2 - srcBitmap.getWidth() / 2;
y = MeasureUtil.getScreenSize((Activity) mContext)[1] / 2 - srcBitmap.getHeight() / 2;
}

@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
// 先绘制阴影
canvas.drawBitmap(shadowBitmap, x, y, shadowPaint);

// 再绘制位图
canvas.drawBitmap(srcBitmap, x, y, null);
}
}