How to create smooth rounded corners on a popup widget in Qt

Question

I have a widget with the `windowsflag` `Qt::Popup` set, and I'm trying to create smooth rounded corners. I've tried using a stylesheet, but then the transparent part of the corners become black. The same happens if I overwrite the widget's paint event and draw a rectangle with rounded corners in the widget. I've also tried to set a mask, but the result gets very pixelated. After some reading, I found out that the black corners appears because the widget is a top-level widget. But I would think that it's still possible somehow? How can I either get rid of the black corners or to smoothen the mask? The paint event: ``` void PopUp::paintEvent(QPaintEvent *event) { QPainter painter(this); QColor greyColor(0xFFC5C6C6); QRect rect(0, 0, width(), height()); painter.setRenderHint(QPainter::Antialiasing); painter.setBrush(QBrush(greyColor)); painter.setPen(QPen(greyColor)); painter.drawRoundedRect(rect, 10, 10); } ``` The function that sets the mask: ``` void PopUp::setRoundedCorners(int radiu…

Accepted Answer

1. Create a widget and set its windowFlags to `Qt::Window | Qt::FramelessWindowHint`, and its attribute to `Qt::WA_TranslucentBackground`.

2. Create a `QFrame` inside of a widget.

3. Set a stylesheet to `QFrame`, for example:

```
border: 1px solid red;
border-radius: 20px;
background-color: black;
```

How to create smooth rounded corners on a popup widget in Qt

Solution

Problem