Android implements dynamic Gaussian blur background effect

android {
  defaultConfig {
    renderscriptTargetApi 21
    renderscriptSupportModeEnabled true
  }
}

// ==============================================
// document:// Function: Demonstrate the use of dynamic Gaussian blurred background// Includes: layout XML, Gradle configuration, BlurView control source code// ==============================================
 
package ;
 
import ;
import ;
import ;
import ;
import ;
 
/*
 ===================================================================
 android {
   compileSdk 33
   defaultConfig {
     applicationId ""
     minSdk 21
     targetSdk 33
     // Enable RenderScript compatibility mode
     renderscriptTargetApi 21
     renderscriptSupportModeEnabled true
   }
   // ...
 }
 dependencies {
   implementation ':appcompat:1.5.1'
   implementation ':gson:2.9.0' // If you need JSON parsing
 }
 ==================================================================
 */
 
/*
 ==================================== res/layout/activity_main.xml ===================================
 <?xml version="1.0" encoding="utf-8"?>
 <!-- Parent layout: Background content -->
 <FrameLayout xmlns:andro
     xmlns:app="/apk/res-auto"
     android:
     android:layout_width="match_parent"
     android:layout_height="match_parent">
     <!-- 1. Background content example -->
     <ImageView
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         android:scaleType="centerCrop"
         android:src="@drawable/your_large_image"/>
     <!-- 2. Dynamic blur mask layer -->
     <
         android:
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         app:blurRadius="16"
         app:downsampleFactor="4"
         app:updateInterval="100"/>
     <!-- 3. Front-end UI elements -->
     <TextView
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:text="dynamic Gaussian fuzzy example"
         android:textSize="24sp"
         android:textColor="#FFFFFFFF"
         android:layout_gravity="center"/>
 </FrameLayout>
 ========================================================================
 */
 
public class BlurDemoActivity extends AppCompatActivity {
    @Override protected void onCreate(@Nullable Bundle s) {
        (s);
        setContentView(.activity_main);
        // No extra code is required, BlurView will work automatically when attached    }
}
 
// ==============================================
// document:// Function: Universal dynamic Gaussian blur mask control// ==============================================
 
package ;
 
import ;
import ;
import .*;
import ;
import .*;
import ;
import .*;
import ;
 
import ;
 
public class BlurView extends FrameLayout {
 
    private int blurRadius;         // Fuzzy radius    private int downsampleFactor;   // Downsampling multiple    private long updateInterval;    // Update interval 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  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);
        // Read properties        TypedArray a = (attrs, );
        blurRadius       = (.BlurView_blurRadius, 10);
        downsampleFactor = (.BlurView_downsampleFactor, 4);
        updateInterval   = (.BlurView_updateInterval, 100);
        ();
 
        // Decide which fuzzy method to use        useRenderEffect = .SDK_INT &gt;= Build.VERSION_CODES.S;
 
        if (!useRenderEffect) {
            // Initialize RenderScript Fuzzy            rs = (c);
            instBlur = (rs, Element.U8_4(rs));
            (blurRadius);
        }
 
        setWillNotDraw(false); // onDraw allowed    }
 
    @Override
    protected void onAttachedToWindow() {
        ();
        // Register PreDraw Monitor        preDrawListener = () -&gt; {
            long now = ();
            if (now - lastUpdateTime &gt;= updateInterval) {
                lastUpdateTime = now;
                blurAndInvalidate();
            }
            return true;
        };
        getViewTreeObserver().addOnPreDrawListener(preDrawListener);
    }
 
    @Override
    protected void onDetachedFromWindow() {
        ();
        // Clean up        getViewTreeObserver().removeOnPreDrawListener(preDrawListener);
        if (rs != null) ();
    }
 
    /** Perform blur and redraw yourself */
    private void blurAndInvalidate() {
        // Get a snapshot of the parent container        View root = (View) getParent();
        if (root == null) return;
 
        int width  = ();
        int height = ();
        if (width == 0 || height == 0) return;
 
        int bw = width  / downsampleFactor;
        int bh = height / downsampleFactor;
 
        // Initialize cache        if (bitmapBuffer == null ||
            ()!=bw ||
            ()!=bh) {
            bitmapBuffer = (bw, bh, .ARGB_8888);
            bitmapCanvas = new Canvas(bitmapBuffer);
        }
        // Draw root zoom to bitmap        ();
        (1f/downsampleFactor, 1f/downsampleFactor);
        (bitmapCanvas);
        ();
 
        // Vague        if (useRenderEffect) {
            // API 31+: Set RenderEffect directly on yourself            RenderEffect effect = (
                blurRadius, blurRadius, );
            setRenderEffect(effect);
        } else {
            // RenderScript blur            if (allocIn!=null) ();
            if (allocOut!=null) ();
            allocIn  = (rs, bitmapBuffer);
            allocOut = (rs, ());
            (allocIn);
            (allocOut);
            (bitmapBuffer);
            // Copy the fuzzy results to your own bitmap            invalidate();
        }
    }
 
    @Override
    protected void onDraw(Canvas canvas) {
        (canvas);
        if (!useRenderEffect &amp;&amp; bitmapBuffer!=null) {
            // Draw and zoom back to the screen            ();
            (downsampleFactor, downsampleFactor);
            (bitmapBuffer, 0, 0, paint);
            ();
        }
    }
}
 
// ==============================================
// res/values/ (integrated here)// ==============================================
/*
&lt;resources&gt;
  &lt;declare-styleable name="BlurView"&gt;
    &lt;attr name="blurRadius" format="integer"/&gt;
    &lt;attr name="downsampleFactor" format="integer"/&gt;
    &lt;attr name="updateInterval" format="integer"/&gt;
  &lt;/declare-styleable&gt;
&lt;/resources&gt;
*/