Paint paint = new Paint();
paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.XXX);
canvas.drawBitmap(srcBmp, rc, rc, paint);

Bitmap roundThumbBitmap = Bitmap.createBitmap(
  rc.width(), rc.height(), Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(roundThumbBitmap);

Paint paint = new Paint();
paint.setColor(0xFFFF0000);  // 任何不透明的颜色均可。（作为掩码色）
paint.setAntiAlias(true);   // 开启抗锯齿,防止圆角毛躁.

// 填充一个圆角矩形.
final float radius = 5.0f;
canvas.drawRoundRect(new RectF(rc), radius, radius, paint);

paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
canvas.drawBitmap(srcBmp, rc, rc, paint);

Bitmap rollAngleThumbBmp = Bitmap.createBitmap(rc.width(), rc.height(), Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(rollAngleThumbBmp);

Bitmap maskBmp = BitmapFactory.decodeResource(context.getResources(), R.drawable.mask);
Bitmap borderBmp = ((BitmapDrawable)context.getResources().getDrawable(R.drawable.border)).getBitmap();

Paint paint = new Paint();
paint.setAntiAlias(true);

// 先贴掩码图.
canvas.drawBitmap(maskBmp, rc, rc, paint);

// 再用 SrcIn 的模式贴缩略图.
paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
canvas.drawBitmap(srcBmp, rc, rc, paint);

// 先取消 Xfermode.
paint.setXfermode(null);

// 再贴边框卷角图.
canvas.drawBitmap(borderBmp, rc, rc, paint);