android - 绘制图像时绘制外部阴影

Question

我目前通过在 Canvas 上绘制来在我的应用中创建一个圆形版本的图像。我想在图像周围画一个微弱的外部阴影，但我不能完全正确。我有两个问题: 1.如何画外阴影(我好像只能画一个x或y偏移量的阴影) 2.我怎样才能画出阴影，使它没有附图中显示的伪影。代码:

![public Bitmap getRoundedCornerBitmap(Bitmap bitmap, float cornerRadius) {
        Bitmap output = Bitmap.createBitmap(bitmap.getWidth()+6, bitmap.getHeight() +6, Config.ARGB_8888);
        Canvas canvas = new Canvas(output);

        final int color = 0xff424242;
        int shadowRadius = getDipsFromPixel(3);
        final Rect imageRect = new Rect(shadowRadius, shadowRadius, bitmap.getWidth(), bitmap.getHeight());
        final RectF rectF = new RectF(imageRect);

        // This does not achieve the desired effect
        Paint shadowPaint = new Paint();
        shadowPaint.setAntiAlias(true);
        shadowPaint.setColor(Color.BLACK);
        shadowPaint.setShadowLayer((float)shadowRadius, 2.0f, 2.0f,Color.BLACK);
        canvas.drawOval(rectF, shadowPaint);

        canvas.drawARGB(0, 0, 0, 0);
        final Paint paint = new Paint();
        paint.setAntiAlias(true);
        paint.setColor(color);

        canvas.drawRoundRect(rectF, cornerRadius, cornerRadius, paint);

        paint.setXfermode(new PorterDuffXfermode(Mode.SRC_IN));
        canvas.drawBitmap(bitmap, imageRect, imageRect, paint);

        return output;
    }][1]

这是我试图达到的效果的一个例子:

Answer 1

我想要类似的效果，但在 AppWidget 上很遗憾我无法使用@EvelioTarazona 的解决方案。这是我想出的，它应该适用于任何形状的位图。

    final Bitmap src = BitmapFactory.decodeResource(getResources(), R.drawable.ic_launcher);
    final Bitmap shadow = addShadow(src, src.getHeight(), src.getWidth(), Color.BLACK, 3, 1, 3);
    final ImageView iv = (ImageView)findViewById(R.id.image);
    iv.setImageBitmap(shadow);

 public Bitmap addShadow(final Bitmap bm, final int dstHeight, final int dstWidth, int color, int size, float dx, float dy) {
    final Bitmap mask = Bitmap.createBitmap(dstWidth, dstHeight, Config.ALPHA_8);

    final Matrix scaleToFit = new Matrix();
    final RectF src = new RectF(0, 0, bm.getWidth(), bm.getHeight());
    final RectF dst = new RectF(0, 0, dstWidth - dx, dstHeight - dy);
    scaleToFit.setRectToRect(src, dst, ScaleToFit.CENTER);

    final Matrix dropShadow = new Matrix(scaleToFit);
    dropShadow.postTranslate(dx, dy);

    final Canvas maskCanvas = new Canvas(mask);
    final Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
    maskCanvas.drawBitmap(bm, scaleToFit, paint);
    paint.setXfermode(new PorterDuffXfermode(Mode.SRC_OUT));
    maskCanvas.drawBitmap(bm, dropShadow, paint);

    final BlurMaskFilter filter = new BlurMaskFilter(size, Blur.NORMAL);
    paint.reset();
    paint.setAntiAlias(true);
    paint.setColor(color);
    paint.setMaskFilter(filter);
    paint.setFilterBitmap(true);

    final Bitmap ret = Bitmap.createBitmap(dstWidth, dstHeight, Config.ARGB_8888);
    final Canvas retCanvas = new Canvas(ret);
    retCanvas.drawBitmap(mask, 0,  0, paint);
    retCanvas.drawBitmap(bm, scaleToFit, null);
    mask.recycle();
    return ret;
}