Android 背景虚化实现

需求：

弹出dialog或者其他一个页面，UI背景显示虚化。

注意：这里虚化并不等于暗化，暗化比较简单通过设置FLAG_DIM_BEHIND即可。

在Andorid 4.1 之前（SDK_INT <16），背景虚化可以使用FLAG_BLUR_BEHIND实现的，但是后续版本Android不再支持，因此才有这篇文章的做法。

解决方案：

step1：获取当前UI的bitmap

step2：将bitmap进行虚化处理

step3：将虚化的bitmap设置为背景即可

这里提供一个工具类，帮助完成前两步，最后一步虚化的bitmap怎么使用，就又使用者来决定了。

示例代码：

/**
使用示例如下
1. 直接调用BlurUtil的getBlurBackground即可，
注意这里需要传入的是一个activity对象
2. dialog注意要设置全屏才能达到显示效果，因为设置的是dialog背景
*/
public class MainActivity extends AppCompatActivity {

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

        findViewById(R.id.textView).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //通过工具类，获取虚化的bitmap
                Bitmap bitmap = BlurUtil.getBlurBackground(MainActivity.this);
                //将虚化的bitmap 设置为背景
                CustDialog dialog = new CustDialog(MainActivity.this, R.style.Dialog_Fullscreen, bitmap);
                dialog.setTitle("blur behind dialog");
                dialog.show();
            }
        });
    }
}

 

 

实际效果：

BlurUtil源码：

/**

这是BlurUtil的源码，对外提供一个getBlurBackground的public方法。
*/
import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.os.Build.VERSION;
import android.renderscript.Allocation;
import android.renderscript.Element;
import android.renderscript.RenderScript;
import android.renderscript.ScriptIntrinsicBlur;
import android.view.View;

public class BlurUtil {

	public static Bitmap getBlurBackground(Activity activity) {
		Bitmap originBitmap = getBackground(activity);
		Bitmap blurBitmap = BlurUtil.apply(activity, originBitmap, 25);
		return blurBitmap;
	}

	private static Bitmap getBackground(Activity activity) {
		View decorView = activity.getWindow().getDecorView();
		decorView.setDrawingCacheQuality(View.DRAWING_CACHE_QUALITY_LOW);
		decorView.setDrawingCacheEnabled(true);
		decorView.buildDrawingCache();
		Bitmap image = decorView.getDrawingCache();
		return image;
	}

	private static Bitmap apply(Context context, Bitmap sentBitmap) {
		return apply(context, sentBitmap, 10);
	}

	private static Bitmap apply(Context context, Bitmap sentBitmap, int radius) {

        Bitmap bitmap = Bitmap.createScaledBitmap(sentBitmap, sentBitmap.getWidth()/2, sentBitmap.getHeight()/2, false);

		if (VERSION.SDK_INT > 16) {
			final RenderScript rs = RenderScript.create(context);
			final Allocation input = Allocation.createFromBitmap(rs, bitmap, Allocation.MipmapControl.MIPMAP_NONE,
					Allocation.USAGE_SCRIPT);
			final Allocation output = Allocation.createTyped(rs, input.getType());
			final ScriptIntrinsicBlur script = ScriptIntrinsicBlur.create(rs, Element.U8_4(rs));
			script.setRadius(radius);
			script.setInput(input);
			script.forEach(output);
			output.copyTo(bitmap);
                        
                        //After finishing everything, we destroy the Renderscript.
                        rs.destroy();
			return bitmap;
		}

		if (radius < 1) {
			return (null);
		}

		int w = bitmap.getWidth();
		int h = bitmap.getHeight();

		int[] pix = new int[w * h];
		bitmap.getPixels(pix, 0, w, 0, 0, w, h);

		int wm = w - 1;
		int hm = h - 1;
		int wh = w * h;
		int div = radius + radius + 1;

		int r[] = new int[wh];
		int g[] = new int[wh];
		int b[] = new int[wh];
		int rsum, gsum, bsum, x, y, i, p, yp, yi, yw;
		int vmin[] = new int[Math.max(w, h)];

		int divsum = (div + 1) >> 1;
		divsum *= divsum;
		int dv[] = new int[256 * divsum];
		for (i = 0; i < 256 * divsum; i++) {
			dv[i] = (i / divsum);
		}

		yw = yi = 0;

		int[][] stack = new int[div][3];
		int stackpointer;
		int stackstart;
		int[] sir;
		int rbs;
		int r1 = radius + 1;
		int routsum, goutsum, boutsum;
		int rinsum, ginsum, binsum;

		for (y = 0; y < h; y++) {
			rinsum = ginsum = binsum = routsum = goutsum = boutsum = rsum = gsum = bsum = 0;
			for (i = -radius; i <= radius; i++) {
				p = pix[yi + Math.min(wm, Math.max(i, 0))];
				sir = stack[i + radius];
				sir[0] = (p & 0xff0000) >> 16;
				sir[1] = (p & 0x00ff00) >> 8;
				sir[2] = (p & 0x0000ff);
				rbs = r1 - Math.abs(i);
				rsum += sir[0] * rbs;
				gsum += sir[1] * rbs;
				bsum += sir[2] * rbs;
				if (i > 0) {
					rinsum += sir[0];
					ginsum += sir[1];
					binsum += sir[2];
				} else {
					routsum += sir[0];
					goutsum += sir[1];
					boutsum += sir[2];
				}
			}
			stackpointer = radius;

			for (x = 0; x < w; x++) {

				r[yi] = dv[rsum];
				g[yi] = dv[gsum];
				b[yi] = dv[bsum];

				rsum -= routsum;
				gsum -= goutsum;
				bsum -= boutsum;

				stackstart = stackpointer - radius + div;
				sir = stack[stackstart % div];

				routsum -= sir[0];
				goutsum -= sir[1];
				boutsum -= sir[2];

				if (y == 0) {
					vmin[x] = Math.min(x + radius + 1, wm);
				}
				p = pix[yw + vmin[x]];

				sir[0] = (p & 0xff0000) >> 16;
				sir[1] = (p & 0x00ff00) >> 8;
				sir[2] = (p & 0x0000ff);

				rinsum += sir[0];
				ginsum += sir[1];
				binsum += sir[2];

				rsum += rinsum;
				gsum += ginsum;
				bsum += binsum;

				stackpointer = (stackpointer + 1) % div;
				sir = stack[(stackpointer) % div];

				routsum += sir[0];
				goutsum += sir[1];
				boutsum += sir[2];

				rinsum -= sir[0];
				ginsum -= sir[1];
				binsum -= sir[2];

				yi++;
			}
			yw += w;
		}
		for (x = 0; x < w; x++) {
			rinsum = ginsum = binsum = routsum = goutsum = boutsum = rsum = gsum = bsum = 0;
			yp = -radius * w;
			for (i = -radius; i <= radius; i++) {
				yi = Math.max(0, yp) + x;

				sir = stack[i + radius];

				sir[0] = r[yi];
				sir[1] = g[yi];
				sir[2] = b[yi];

				rbs = r1 - Math.abs(i);

				rsum += r[yi] * rbs;
				gsum += g[yi] * rbs;
				bsum += b[yi] * rbs;

				if (i > 0) {
					rinsum += sir[0];
					ginsum += sir[1];
					binsum += sir[2];
				} else {
					routsum += sir[0];
					goutsum += sir[1];
					boutsum += sir[2];
				}

				if (i < hm) {
					yp += w;
				}
			}
			yi = x;
			stackpointer = radius;
			for (y = 0; y < h; y++) {
				// Preserve alpha channel: ( 0xff000000 & pix[yi] )
				pix[yi] = (0xff000000 & pix[yi]) | (dv[rsum] << 16) | (dv[gsum] << 8) | dv[bsum];

				rsum -= routsum;
				gsum -= goutsum;
				bsum -= boutsum;

				stackstart = stackpointer - radius + div;
				sir = stack[stackstart % div];

				routsum -= sir[0];
				goutsum -= sir[1];
				boutsum -= sir[2];

				if (x == 0) {
					vmin[y] = Math.min(y + r1, hm) * w;
				}
				p = x + vmin[y];

				sir[0] = r[p];
				sir[1] = g[p];
				sir[2] = b[p];

				rinsum += sir[0];
				ginsum += sir[1];
				binsum += sir[2];

				rsum += rinsum;
				gsum += ginsum;
				bsum += binsum;

				stackpointer = (stackpointer + 1) % div;
				sir = stack[stackpointer];

				routsum += sir[0];
				goutsum += sir[1];
				boutsum += sir[2];

				rinsum -= sir[0];
				ginsum -= sir[1];
				binsum -= sir[2];

				yi += w;
			}
		}

		bitmap.setPixels(pix, 0, w, 0, 0, w, h);
		return (bitmap);
	}
}