QPainter blend color

Question

Th QPainter drawns are superposed when drawn. How can I mix colors when drawing? For example: If there is a green line drawn and a red line is drawn afterwards in the same position, the colour of the line will be red, I would like to get a mix of red and green.

Answer 1

The colors are not superimposed but painted over, and that happens when they are opaque.
As soon as you use a color with an alpha value less than 255, the colors are "mixed".

pixmap = QtGui.QPixmap(200, 200)
pixmap.fill(QtCore.Qt.black)
qp = QtGui.QPainter(pixmap)
qp.setRenderHints(qp.Antialiasing)
qp.setPen(QtCore.Qt.NoPen)
qp.setBrush(QtGui.QColor(255, 0, 0, 85))
qp.drawEllipse(40, 0, 120, 120)
qp.setBrush(QtGui.QColor(0, 255, 0, 85))
qp.drawEllipse(0, 80, 120, 120)
qp.setBrush(QtGui.QColor(0, 0, 255, 85))
qp.drawEllipse(80, 80, 120, 120)
qp.end()