private static Bitmap getCircleAvatar(Context context, Bitmap avatar) {
// TODO Auto-generated method stub
Bitmap bitmap=Bitmap.createBitmap(avatar.getWidth(), avatar.getHeight(), Bitmap.Config.ARGB_8888);
Canvas canvas=new Canvas(bitmap);
Paint paint=new Paint(Paint.ANTI_ALIAS_FLAG);
//混合模式中的圓 DST
paint.setColor(Color.BLACK);
//半徑取寬高中小的並/2
canvas.drawCircle(avatar.getWidth()/2, avatar.getHeight()/2,
avatar.getWidth()/2<avatar.getHeight()/2?avatar.getWidth()/2:avatar.getHeight()/2,
paint);
//新增混合模式給paint，矩陣，切圓，方形和圓形，選擇圓形重疊的部分
//PorterDuffXfermode：該方法及是
paint.setXfermode(new PorterDuffXfermode(Mode.SRC_IN));
//再把原始頭像，畫到bitmap上
canvas.drawBitmap(avatar, 0, 0, paint);
/**畫個百邊*/
paint.setColor(Color.WHITE);
paint.setStyle(Paint.Style.STROKE);//設定一個模式
//進行單位變換

float strokeWidth = 
TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 2, 
context.getResources().getDisplayMetrics());
paint.setStrokeWidth(strokeWidth);
canvas.drawCircle(avatar.getWidth()/2, avatar.getHeight()/2,
avatar.getWidth()/2<avatar.getHeight()/2?avatar.getWidth()/2:avatar.getHeight()/2
-strokeWidth/2, paint);
return bitmap;
}