[Interest] First Paint Event: custom shaped widget

[Sensei]

Dear all,

in a previous post (Masked widget glitch) I asked suggestions about 
making an arrow-like widget (see picture in [1]). The old and bad code 
used a mask, but it had a glitch, as you see in the picture; however, 
the workaround was easy: doing show, hide, show. Ugly but it worked.

I was suggested to move my code to a new QWidget subclass, painting the 
background, but now I'm finding it hard to create even the simplest form.

What I've achieved so far is very lousy (see picture in [2]): the ugly 
hack I've used before seems better than this one.

Can anyone help me understand how to draw a good-looking widget?

Thanks & Cheers!

[1] https://dl.dropboxusercontent.com/u/15635416/mask.png
[2] https://dl.dropboxusercontent.com/u/15635416/paint.png


ToolWindow::ToolWindow(QWidget *parent, QWidget *follow) : 
QWidget(parent, Qt::FramelessWindowHint)
{
     setAttribute(Qt::WA_TranslucentBackground);
}

void ToolWindow::paintEvent(QPaintEvent *event)
{
     QPainter p(this);

     const int h = 10;
     const int w  = 12;

     QPoint path[7];

     path[0] = QPoint(      0,        h);
     path[1] = QPoint(  w    ,        h);
     path[2] = QPoint(  w * 2,        0);
     path[3] = QPoint(  w * 3,        h);
     path[4] = QPoint(width(),        h);
     path[5] = QPoint(width(), height());
     path[6] = QPoint(      0, height());

     p.drawPolygon(path, 7);
}