I get exactly what you're dealing with—trying to make a nice rounded message box that sits on top of your main player widget without those ugly rectangular backgrounds or pixelated edges can be tricky. Let's fix this properly.

Why Your Previous Approaches Failed #

• QFrame with background:transparent: This doesn't work because Qt doesn't enable transparent backgrounds for widgets by default. Without setting the right attribute, even if you set border-radius, the underlying widget rectangle remains opaque, which is why you saw that square background.
• QRegion Mask: QRegion only handles basic geometric shapes, so it can't produce smooth rounded corners (the "squircles" you want) without pixelation. It's just not designed for anti-aliased, smooth edges.

The Correct Solution #

We'll use Qt's WA_TranslucentBackground attribute combined with a properly written stylesheet to get smooth, transparent rounded corners, and ensure the message box sits on top of your player widget.

Updated Message Class

from PyQt5.QtWidgets import QFrame, QVBoxLayout, QLabel, QWidget
from PyQt5.QtCore import Qt, QTimer

# Assume Fonts and Colors are your global style definitions
class Message(QFrame):
    """
    A temporary, overlayed message box with smooth rounded corners.
    """
    def __init__(self, msg: str, parent=None, destroy_time: int = 3000):
        super().__init__(parent)
        
        # Critical: Enable translucent background to allow transparent regions
        self.setAttribute(Qt.WA_TranslucentBackground)
        # Remove default window border to avoid extra rectangular space
        self.setWindowFlags(Qt.FramelessWindowHint)
        
        # Layout setup
        self.layout = QVBoxLayout(self)
        self.layout.setContentsMargins(20, 20, 20, 20)
        self.layout.setSpacing(0)

        # Message label
        label = QLabel(msg)
        label.setFont(Fonts.text)
        label.setStyleSheet(f"color: {Colors.fg};")
        self.layout.addWidget(label)

        # Stylesheet: Use RGBA for background (last value = opacity) + rounded corners
        # Replace the RGBA value with your desired background color and opacity
        self.setStyleSheet(f"""
            QFrame {{
                background-color: rgba(20, 20, 20, 0.9); 
                border-radius: 30px;
            }}
        """)

        self.adjustSize()
        
        # Auto-destroy after specified time (default 3 seconds)
        if destroy_time is not None:
            QTimer.singleShot(destroy_time, self.deleteLater)
    
    def showEvent(self, event):
        # Center the message box on its parent widget when shown
        if self.parent():
            parent_center = self.parent().rect().center()
            self.move(parent_center - self.rect().center())
        super().showEvent(event)

Updated MainWindow Usage

class MainWindow(QWidget):
    def __init__(self, player: QWidget):
        super().__init__()
        layout = QHBoxLayout(self)
        layout.setContentsMargins(0, 0, 0, 0)
        layout.setSpacing(0)
        layout.addWidget(player)

        # Create and show the message box
        msg = Message("It works now!", self)
        # Ensure the message box is drawn on top of the player
        msg.raise_()
        msg.show()

Key Details to Note #

1. WA_TranslucentBackground: This is the magic switch that tells Qt to allow transparent areas in the widget. Without it, your border-radius will just clip the content but leave the background as an opaque square.
2. RGBA Background: Using an RGBA color for the background lets you control opacity, so you can still see the player widget underneath the message box. Adjust the last value (0.9 in the example) to make it more or less transparent.
3. raise_() Method: This ensures the message box is placed above the player widget in the Z-order, so it actually overlays instead of being hidden underneath.
4. Centering: The showEvent override automatically centers the message box on its parent, which makes it look clean over your player.

内容的提问来源于stack exchange，提问作者Dewamuval