自定义控件（7）---BlurMaskFilter边界阴影

本文主要是介绍自定义控件（7）---BlurMaskFilter边界阴影，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

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.MaskFilterViewandroid: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 {@Overrideprotected 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;}@Overrideprotected 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HWsetLayerType(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;}@Overrideprotected 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SOFTWAREsetLayerType(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;}@Overrideprotected 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);}
}

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