[FIXED] Draw a border around all objects/shapes in a QGraphicsItem paint method

Issue

I want to draw a border around all objects/shapes within a QGraphicsItem Paint method. (The green and red circles are part of a separate item, so they don't count in this situation)

I am currently drawing RoundedRects, but I'm looking for a scalable solution that could also support more complicated objects (stars, bananas, etc); situations where you have objects overlaid on each other.

I have an Item that, when selected, changes the border colour of two RoundedRects.

I want a solution where only the outline border changes colour, not the internal.

Possible methods I think might work are using a QGraphicsDropShadowEffect or creating a QtCore.Qt.MaskOutColor and controlling the line thickness, somehow. I've done this before by scaling up a duplicate masked shape, but the results aren't ideal. So I'd be really interested in hearing other people's solutions!

This is my basic QGraphicsItem.

class Node(QtWidgets.QGraphicsItem):
    def __init__(self, scene, parent=None):
        super(Node, self).__init__(parent)

        scene.addItem(self)

        # Variables
        self.main_background_colour = QtGui.QColor(31, 176, 224)
        self.title_background_colour = QtGui.QColor("#fffeb3")
        self.name_background_colour = QtGui.QColor("#b8b64b")
        self.brush = QtGui.QBrush(self.main_background_colour)
        self.pen = QtGui.QPen(self.title_text_colour, 2)

        self.main_rect = QtCore.QRectF(0, 0, 400, 200)
        self.title_rect = QtCore.QRectF(self.main_rect.x() + (self.main_rect.width() * 0.05), self.main_rect.y() - 10, (self.main_rect.width() * 0.9), (self.main_rect.height() * 0.2))
        self.name_rect = QtCore.QRectF(self.main_rect.x() + (self.main_rect.width() * 0.02), self.title_rect.bottom() - 10, (self.main_rect.width() * 0.96), (self.main_rect.height() * 0.3))
        self.name_font_rect = QtCore.QRectF(self.name_rect.x() + (self.name_rect.width() * 0.05), self.name_rect.y() + 10, self.name_rect.width() * 0.9, self.name_rect.height() * 0.65)

        # Flags
        self.setFlag(self.ItemIsMovable, True)
        self.setFlag(self.ItemSendsGeometryChanges, True)
        self.setFlag(self.ItemIsSelectable, True)
        self.setFlag(self.ItemIsFocusable, True)

        self.setCacheMode(QtWidgets.QGraphicsItem.DeviceCoordinateCache)

    def boundingRect(self):
        return QtCore.QRectF(self.main_rect.x(), self.title_rect.y(), self.main_rect.width(), self.main_rect.height() + abs(self.main_rect.y() + self.title_rect.y()))

    def paint(self, painter, option, widget=None):

        # Border
        if self.isSelected():
            border_colour = QtGui.QColor(241, 175, 0)

        else:
            border_colour = self.main_background_colour.lighter()

        self.pen.setColor(border_colour)
        self.pen.setWidth(2)
        painter.setPen(self.pen)

        # Background
        self.brush.setColor(self.main_background_colour)
        painter.setBrush(self.brush)
        painter.drawRoundedRect(self.main_rect, 4, 4)

        # Name
        self.brush.setColor(self.name_background_colour)
        painter.setBrush(self.brush)
        self.pen.setColor(QtGui.QColor("black"))
        painter.setPen(self.pen)
        painter.drawRoundedRect(self.name_rect, 4, 4)


        # Tile
        self.brush.setColor(self.title_background_colour)
        painter.setBrush(self.brush)
        self.pen.setColor(border_colour)
        painter.setPen(self.pen)

        painter.drawRoundedRect(self.title_rect, 4, 4)

UPDATE I have tried using the paint method as shown in musicamante answer, but it draws a border around all Rects individually, rather than the overall exterior shape.

The rest of my base code is the same, but I have changed the paint to match musicamante reply.

def paint(self, painter, option, widget=None):

    path = QtGui.QPainterPath()
    path.setFillRule(QtCore.Qt.WindingFill)

    for rect in (self.main_rect, self.name_rect, self.title_rect):
        path.addRoundedRect(rect, 4, 4)

    if self.isSelected():
        border_colour = QtGui.QColor(241, 175, 0)
    else:
        border_colour = self.main_background_colour.lighter()

    painter.setPen(QtGui.QPen(border_colour, 2))
    painter.drawPath(path)

To clarify, this is the border I am trying to achieve:

Solution

The simplest (but yet not optimal) solution is to create a QPainterPath based on all the rectangles, and draw the "final" border joining all the shapes the item contains:

    def paint(self, painter, option, widget=None):
        # draw all items here, using default values
        # ...

        path = QtGui.QPainterPath()
        path.setFillRule(Qt.WindingFill)

        for rect in (self.main_rect, self.name_rect, self.title_rect):
            path.addRoundedRect(rect, 4, 4)

        if self.isSelected():
            border_colour = QtGui.QColor(241, 175, 0)
        else:
            border_colour = self.main_background_colour.lighter()

        painter.setPen(QtGui.QPen(border_colour, 2))
        painter.drawPath(path.simplified())

Be aware, though, that painting functions are called very often. Some level of caching and existing implementation is always preferred, especially considering that python is a huge bottleneck: you should always try to take advantage of the C++ implementation, possibly with existing base QGraphicsItem shapes.

For instance, instead of always painting three rounded rects from python, you could use a QGraphicsPathItem with a predefined QGraphicsPath set for each item.

Since you're already setting the ItemSendsGeometryChanges flag, you could override itemChange() to update that path whenever required, so that you don't need to create a new QPainterPath object for every paint() call.

And if those items are used to show text, then use a QGraphicsPathItem with a QGraphicsSimpleTextItem set as a child of it.

Alternatively, consider using a QPicture as a class/instance variable that would be used as a "middle-cache" object: while it might add some level of complexity in the implementation, it certainly would improve performance, especially when multiple items are being shown.

Answered By - musicamante