QWidget PaintEvent CompositionMode "masking" issue

calier

Hi !

I'm trying to use QPainter to draw a custom widget and use the compositionMode as a mask to what I painted.
I tried pretty much all combos and I can't quite figure out how to do it.
Attached is a trimmed down version of my code and a picture to explain my issue.

The idea is to paint a few shapes and "mask" the result with another shape.

EDIT: Qt's examples set the "compositionMode" on QImages rather than directly within a QWidget's paintEvent which is a pretty slow method especially when resizing the window, etc ...
I don't see anything in the QPainter's documentation saying that you can't use it the way I am using it. Does anybody knows why this isn't working ?

(FYI: my goal isn't to create a simple bar with rounded corners as my screenshots suggests. This is just a stripped down version of my code to demonstrate my problem)

Any help would be greatly appreciated, thanks !

import sys

try:
    import PySide2
    from PySide2.QtCore import *
    from PySide2.QtGui import *
    from PySide2.QtWidgets import *
except:
    import PySide
    from PySide.QtCore import *
    from PySide.QtGui import *

class SomeCustomWidget(QWidget):
    def __init__(self, parent = None):
        QWidget.__init__(self , parent)

        self.setMaximumHeight(28)
        self.setAttribute(Qt.WA_TranslucentBackground)

    def paintEvent(self, e):
        rect = self.rect()

        painter = QPainter()
        painter.begin(self)

        painter.setBackgroundMode(Qt.TransparentMode)
        painter.setRenderHint(QPainter.Antialiasing)
        painter.setRenderHint(QPainter.HighQualityAntialiasing)

        painter.setCompositionMode(QPainter.CompositionMode_Source)

        painter.setPen(Qt.NoPen)

        # Paint Source
        # Draw a bunch of stuff in there
        painter.setBrush( QColor(128, 200, 255, 255) )
        painter.drawRect(0, 0, rect.width(), rect.height())

        # Set Mask to everything drawned above
        painter.setCompositionMode(QPainter.CompositionMode_SourceIn)
        painter.setBrush( QColor(255, 255, 255, 255) )
        painter.drawRoundedRect(0, 0, rect.width(), rect.height(), 12, 12)

        painter.end()



if __name__ == '__main__':
	app = QApplication(sys.argv)

	custWidget = SomeCustomWidget()

	custWidget.show()
	sys.exit(app.exec_())

calier

It looks like the CompositionModes only work on QImages. Bummer :/

SGaist

Hi,

Depending on what you need, you can draw on a QImage and then draw that image in your custom widget.

What is it that you want to achieve ?