title: How to remove the border of a QDialog which I give a transparent background image?
body: <p>I intended to make a un-rectangle <code>QDialog</code>, so I paint a png image by override <code>QDialog::paintEvent</code>.Everything is okay except there is a gray border shown arrond the dialog.Like this:</p>
  
  <p><img src="https://i.stack.imgur.com/2gL8a.png" alt="enter image description here"></p>
  
  <p>I am sure that border is not belong to the image,and I had <code>setWindowFlags(Qt::FramelessWindowHint)</code> and <code>setAttribute(Qt::WA_TranslucentBackground, true)</code>.I tried to set a qss like <code>border-width: 0px</code> but didn't work.
  Is there any way to remove the border?And why it is shown?</p>