Android 具有渐变透明背景的线性布局

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，然后去它底部的不透明。

布局嵌套在视差滚动视图中，因此布局可以滑过 header 图片的顶部。

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);
            }
        });
    }

模糊生成器如下所示：

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

您可以使用 drawable xml 为您的布局设置渐变，如下所示。

将下面的代码放在文件中说 mybg.xml 并将其放入 drawable 文件夹中。

<shape 
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle"
>
    <gradient
        android:startColor="@color/mycolor1"
        android:endColor="@color/mycolor2"
        android:angle="270" />
</shape>

对颜色使用 8 个字符的哈希码，这样您的颜色就可以像这样

mycolor1 -> #000000aa   //this will give you transparent colored background
mycolor2 -> #ff00aa00   //this will be opaque like background

此处的前两个字符设置颜色的 alpha 级别。

Answer 2

由于您正在操纵 Bitmap 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.

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;
}

Answer 3

可以这样做：

只需确保位图是可变的，同样使用 fadingPortion 值（>= 0 和 <=1）你可以只使背景渐变的一部分透明

    public static Bitmap makeBitmapTransparent(Bitmap mutableBitmap, float fadingPortion) {
    final Shader gradientShader = new LinearGradient(
            mutableBitmap.getWidth() / 2, 0,
            mutableBitmap.getWidth() / 2, mutableBitmap.getHeight() * fadingPortion,
            0x00000000, 0xFF000000,
            Shader.TileMode.CLAMP);

    Paint paint = new Paint();
    paint.setShader(gradientShader);
    paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));

    Canvas canvas = new Canvas(mutableBitmap);
    canvas.drawRect(new Rect(0, 0, mutableBitmap.getWidth(), (int) (mutableBitmap.getHeight() * FADING_PORTION)), paint);
    canvas.drawBitmap(mutableBitmap, 0, 0, null);

    return mutableBitmap;
}

Android 具有渐变透明背景的线性布局

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