Android实现动态高斯模糊背景效果

android {
  defaultconfig {
    renderscripttargetapi 21
    renderscriptsupportmodeenabled true
  }
}

// ==============================================
// 文件：blurdemoactivity.java
// 功能：演示动态高斯模糊背景的使用
// 包含：布局 xml，gradle 配置，blurview 控件源码
// ==============================================
 
package com.example.blurviewdemo;
 
import android.graphics.bitmap;
import android.os.build;
import android.os.bundle;
import androidx.annotation.nullable;
import androidx.appcompat.app.appcompatactivity;
 
/*
=========================== app/build.gradle ===========================
android {
  compilesdk 33
  defaultconfig {
    applicationid "com.example.blurviewdemo"
    minsdk 21
    targetsdk 33
    // 启用 renderscript 兼容模式
    renderscripttargetapi 21
    renderscriptsupportmodeenabled true
  }
  // ...
}
dependencies {
  implementation 'androidx.appcompat:appcompat:1.5.1'
  implementation 'com.google.code.gson:gson:2.9.0' // 如需 json 解析
}
=========================== gradle 结束 ===========================
*/
 
/*
=========================== res/layout/activity_main.xml ===========================
<?xml version="1.0" encoding="utf-8"?>
<!-- 父布局：背景内容 -->
<framelayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/rootcontainer"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <!-- 1. 背景内容示例 -->
    <imageview
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:scaletype="centercrop"
        android:src="@drawable/your_large_image"/>
    <!-- 2. 动态模糊遮罩层 -->
    <com.example.blurviewdemo.blurview
        android:id="@+id/blurview"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:blurradius="16"
        app:downsamplefactor="4"
        app:updateinterval="100"/>
    <!-- 3. 前端 ui 元素 -->
    <textview
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="动态高斯模糊示例"
        android:textsize="24sp"
        android:textcolor="#ffffffff"
        android:layout_gravity="center"/>
</framelayout>
=========================== 布局结束 ===========================
*/
 
public class blurdemoactivity extends appcompatactivity {
    @override protected void oncreate(@nullable bundle s) {
        super.oncreate(s);
        setcontentview(r.layout.activity_main);
        // 无需额外代码，blurview 会在 attached 时自动工作
    }
}
 
// ==============================================
// 文件：blurview.java
// 功能：通用的动态高斯模糊遮罩控件
// ==============================================
 
package com.example.blurviewdemo;
 
import android.content.context;
import android.content.res.typedarray;
import android.graphics.*;
import android.os.build;
import android.renderscript.*;
import android.util.attributeset;
import android.view.*;
import android.widget.framelayout;
 
import androidx.annotation.nullable;
 
public class blurview extends framelayout {
 
    private int blurradius;         // 模糊半径
    private int downsamplefactor;   // 降采样倍数
    private long updateinterval;    // 更新间隔 ms
 
    private bitmap bitmapbuffer;
    private canvas  bitmapcanvas;
    private paint   paint = new paint(paint.anti_alias_flag);
    private boolean userendereffect;
    private renderscript rs;
    private scriptintrinsicblur instblur;
    private allocation allocin, allocout;
 
    private viewtreeobserver.onpredrawlistener predrawlistener;
    private long lastupdatetime = 0;
 
    public blurview(context c) { this(c, null); }
    public blurview(context c, attributeset attrs) { this(c, attrs, 0); }
    public blurview(context c, attributeset attrs, int defstyle) {
        super(c, attrs, defstyle);
        // 读取属性
        typedarray a = c.obtainstyledattributes(attrs, r.styleable.blurview);
        blurradius       = a.getint(r.styleable.blurview_blurradius, 10);
        downsamplefactor = a.getint(r.styleable.blurview_downsamplefactor, 4);
        updateinterval   = a.getint(r.styleable.blurview_updateinterval, 100);
        a.recycle();
 
        // 决定使用哪种模糊方式
        userendereffect = build.version.sdk_int >= build.version_codes.s;
 
        if (!userendereffect) {
            // 初始化 renderscript 模糊
            rs = renderscript.create(c);
            instblur = scriptintrinsicblur.create(rs, element.u8_4(rs));
            instblur.setradius(blurradius);
        }
 
        setwillnotdraw(false); // 允许 ondraw
    }
 
    @override
    protected void onattachedtowindow() {
        super.onattachedtowindow();
        // 注册 predraw 监听
        predrawlistener = () -> {
            long now = system.currenttimemillis();
            if (now - lastupdatetime >= updateinterval) {
                lastupdatetime = now;
                blurandinvalidate();
            }
            return true;
        };
        getviewtreeobserver().addonpredrawlistener(predrawlistener);
    }
 
    @override
    protected void ondetachedfromwindow() {
        super.ondetachedfromwindow();
        // 清理
        getviewtreeobserver().removeonpredrawlistener(predrawlistener);
        if (rs != null) rs.destroy();
    }
 
    /** 执行模糊并重绘自己 */
    private void blurandinvalidate() {
        // 获取父容器快照
        view root = (view) getparent();
        if (root == null) return;
 
        int width  = root.getwidth();
        int height = root.getheight();
        if (width == 0 || height == 0) return;
 
        int bw = width  / downsamplefactor;
        int bh = height / downsamplefactor;
 
        // 初始化缓存
        if (bitmapbuffer == null ||
            bitmapbuffer.getwidth()!=bw ||
            bitmapbuffer.getheight()!=bh) {
            bitmapbuffer = bitmap.createbitmap(bw, bh, bitmap.config.argb_8888);
            bitmapcanvas = new canvas(bitmapbuffer);
        }
        // 将 root 缩放绘制到 bitmap
        bitmapcanvas.save();
        bitmapcanvas.scale(1f/downsamplefactor, 1f/downsamplefactor);
        root.draw(bitmapcanvas);
        bitmapcanvas.restore();
 
        // 模糊
        if (userendereffect) {
            // api 31+: 直接在自己上设置 rendereffect
            rendereffect effect = rendereffect.createblureffect(
                blurradius, blurradius, shader.tilemode.clamp);
            setrendereffect(effect);
        } else {
            // renderscript 模糊
            if (allocin!=null) allocin.destroy();
            if (allocout!=null) allocout.destroy();
            allocin  = allocation.createfrombitmap(rs, bitmapbuffer);
            allocout = allocation.createtyped(rs, allocin.gettype());
            instblur.setinput(allocin);
            instblur.foreach(allocout);
            allocout.copyto(bitmapbuffer);
            // 将模糊结果拷贝到自己的 bitmap
            invalidate();
        }
    }
 
    @override
    protected void ondraw(canvas canvas) {
        super.ondraw(canvas);
        if (!userendereffect && bitmapbuffer!=null) {
            // 绘制放大回屏幕
            canvas.save();
            canvas.scale(downsamplefactor, downsamplefactor);
            canvas.drawbitmap(bitmapbuffer, 0, 0, paint);
            canvas.restore();
        }
    }
}
 
// ==============================================
// res/values/attrs.xml（整合在此）
// ==============================================
/*
<resources>
  <declare-styleable name="blurview">
    <attr name="blurradius" format="integer"/>
    <attr name="downsamplefactor" format="integer"/>
    <attr name="updateinterval" format="integer"/>
  </declare-styleable>
</resources>
*/