使用canvas为图片添加阴影效果

Paint shadowPaint=new Paint();
shadowPaint.setShadowLayer(shadow_radius,4f,4f,Color.GRAY);//关键设置

Canvas canvas=new Canvas(bg);
canvas.drawColor(mContext.getResources().getColor(R.color.white));
//绘制阴影背景
canvas.drawRect(offsetX,offsetY,width+offsetX,height+offsetY,shadowPaint);
//绘制Bitmap
canvas.drawBitmap(bitmap,offsetX,offsetY,null);