具有渐变透明背景的Android线性布局

Question

如何在 android 透明渐变背景中给出线性布局，布局当前有一个模糊图像作为背景，但是我需要模糊图像在布局顶部稍微透明，然后在底部变为不透明

布局嵌套在视差 ScrollView 中，因此布局可以滑过标题图像的顶部。

我像这样生成模糊的可绘制对象:

final View content = img_header;
    if (content.getWidth() > 0) {
        Bitmap image = BlurBuilder.blur(content);
        BitmapDrawable background = new BitmapDrawable(image);

        ll_parent_layout.setBackground(background);
    } else {
        content.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
            @Override
            public void onGlobalLayout() {
                Bitmap image = BlurBuilder.blur(content);
                BitmapDrawable background = new BitmapDrawable(image);
                ll_parent_layout.setBackground(background);
            }
        });
    }

模糊生成器看起来像这样:

public class BlurBuilder {
private static final float BITMAP_SCALE = 1f;
private static final float BLUR_RADIUS = 25f;

public static Bitmap blur(View v) {
    return blur(v.getContext(), getScreenshot(v));
}

public static Bitmap blur(Context ctx, Bitmap image) {
    int width = Math.round(image.getWidth() * BITMAP_SCALE);
    int height = Math.round(image.getHeight() * BITMAP_SCALE);

    Bitmap inputBitmap = Bitmap.createScaledBitmap(image, width, height, false);
    Bitmap outputBitmap = Bitmap.createBitmap(inputBitmap);
     /// compress bitmap here

    RenderScript rs = RenderScript.create(ctx);
    ScriptIntrinsicBlur theIntrinsic = ScriptIntrinsicBlur.create(rs, Element.U8_4(rs));
    Allocation tmpIn = Allocation.createFromBitmap(rs, inputBitmap);
    Allocation tmpOut = Allocation.createFromBitmap(rs, outputBitmap);
    theIntrinsic.setRadius(BLUR_RADIUS);
    theIntrinsic.setInput(tmpIn);
    theIntrinsic.forEach(tmpOut);
    tmpOut.copyTo(outputBitmap);

    return outputBitmap;
}

public static Bitmap blur(Context ctx, Bitmap image, float scale, float radius) {
    int width = Math.round(image.getWidth() * scale);
    int height = Math.round(image.getHeight() * scale);

    Bitmap inputBitmap = Bitmap.createScaledBitmap(image, width, height, false);
    Bitmap outputBitmap = Bitmap.createBitmap(inputBitmap);

    RenderScript rs = RenderScript.create(ctx);
    ScriptIntrinsicBlur theIntrinsic = ScriptIntrinsicBlur.create(rs, Element.U8_4(rs));
    Allocation tmpIn = Allocation.createFromBitmap(rs, inputBitmap);
    Allocation tmpOut = Allocation.createFromBitmap(rs, outputBitmap);
    theIntrinsic.setRadius(radius);
    theIntrinsic.setInput(tmpIn);
    theIntrinsic.forEach(tmpOut);
    tmpOut.copyTo(outputBitmap);

    return outputBitmap;
}


private static Bitmap getScreenshot(View v) {
    Bitmap b = Bitmap.createBitmap(v.getWidth(), v.getHeight(), Bitmap.Config.ARGB_8888);
    Canvas c = new Canvas(b);
    v.draw(c);
    return b;
}
}

Answer 1

由于您正在操作Bitmap 来生成模糊图像，您可以使用LinearGradient 着色器为其添加透明度，如this answer 所示。 .

public Bitmap addGradient(Bitmap src) {
    int w = src.getWidth();
    int h = src.getHeight();
    Bitmap overlay = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(overlay);

    canvas.drawBitmap(src, 0, 0, null);

    Paint paint = new Paint();
    LinearGradient shader = new LinearGradient(0, 0, 0, h, 0xFFFFFFFF, 0x00FFFFFF, Shader.TileMode.REPEAT);
    paint.setShader(shader);
    paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));
    canvas.drawRect(0, h - h, w, h, paint);

    return overlay;
}