QGraphicsPathItem的形状方法中的问题

Question

在下图中，我有 QGraphicsPathItem 场景中的红色部分，并覆盖它的形状为蓝色部分。 我希望当红色空间被拖动并移动时，项目被线性延长或缩短，而当蓝色空间被拖动时，整个项目必须被移动。

import sys

from PyQt5.QtCore import QRectF, Qt, QPointF
from PyQt5.QtGui import QPainterPath, QPen, QPainterPathStroker, QPainter
from PyQt5.QtWidgets import QApplication, QMainWindow, QGraphicsScene, QGraphicsView, QGraphicsPathItem, QGraphicsItem

class Item(QGraphicsPathItem):
    circle = QPainterPath()
    circle.addEllipse(QRectF(-5, -5, 10, 10))

    def __init__(self):
        super(Item, self).__init__()
        self.setPath(Item.circle)
        self.setFlag(QGraphicsItem.ItemIsSelectable, True)
        self.setFlag(QGraphicsItem.ItemIsMovable, True)

    def paint(self, painter, option, widget):
        color = Qt.red if self.isSelected() else Qt.black
        painter.setPen(QPen(color, 2, Qt.SolidLine))
        painter.drawPath(self.path())

        # To paint path of shape
        painter.setPen(QPen(Qt.blue, 1, Qt.SolidLine))
        painter.drawPath(self.shape())

    def shape(self):
        startPoint = self.mapFromScene(self.pos())
        endPoint = self.mapFromScene(QPointF(10, 10))
        path = QPainterPath(startPoint)
        path.lineTo(endPoint)
        stroke = QPainterPathStroker()
        stroke.setWidth(10)
        return stroke.createStroke(path)


if __name__ == "__main__":
    app = QApplication(sys.argv)
    window = QMainWindow()
    window.show()
    scene = QGraphicsScene()
    scene.setSceneRect(0, 0, 200, 200)
    view = QGraphicsView()
    view.setScene(scene)
    window.setCentralWidget(view)
    scene.addItem(Item())
    sys.exit(app.exec_())

我得到的输出是受干扰的路径

Answer 1

在同一个项目中处理调整大小和拉伸的任务很复杂，所以为了避免这种情况，我使用了2个项目。一个手柄和一个管子. 因此，每个项目都管理自己的任务，并更新其他元素的位置。

import sys

from PyQt5 import QtCore, QtGui, QtWidgets


class HandleItem(QtWidgets.QGraphicsPathItem):
    def __init__(self, parent=None):
        super().__init__(parent)
        path = QtGui.QPainterPath()
        path.addEllipse(QtCore.QRectF(-5, -5, 10, 10))
        self.setPath(path)

        self.setFlag(QtWidgets.QGraphicsItem.ItemIsSelectable, True)
        self.setFlag(QtWidgets.QGraphicsItem.ItemIsMovable, True)
        self.setFlag(QtWidgets.QGraphicsItem.ItemSendsGeometryChanges, True)

        self._pipe_item = None

    @property
    def pipe_item(self):
        return self._pipe_item

    @pipe_item.setter
    def pipe_item(self, item):
        self._pipe_item = item

    def itemChange(self, change, value):
        if change == QtWidgets.QGraphicsItem.ItemPositionChange and self.isEnabled():
            ip = self.pipe_item.mapFromScene(value)
            self.pipe_item.end_pos = ip
        elif change == QtWidgets.QGraphicsItem.ItemSelectedChange:
            color = QtCore.Qt.red if value else QtCore.Qt.black
            self.setPen(QtGui.QPen(color, 2, QtCore.Qt.SolidLine))
        return super().itemChange(change, value)


class PipeItem(QtWidgets.QGraphicsPathItem):
    def __init__(self, parent=None):
        super().__init__(parent)

        self.setFlag(QtWidgets.QGraphicsItem.ItemIsSelectable, True)
        self.setFlag(QtWidgets.QGraphicsItem.ItemIsMovable, True)
        self.setFlag(QtWidgets.QGraphicsItem.ItemSendsGeometryChanges, True)

        self._end_pos = QtCore.QPointF()

        self._handle = HandleItem()
        self.handle.pipe_item = self

        self.end_pos = QtCore.QPointF(10, 10)
        self.handle.setPos(self.end_pos)

        self.setPen(QtGui.QPen(QtCore.Qt.blue, 1, QtCore.Qt.SolidLine))

    @property
    def handle(self):
        return self._handle

    @property
    def end_pos(self):
        return self._end_pos

    @end_pos.setter
    def end_pos(self, p):
        path = QtGui.QPainterPath()
        path.lineTo(p)
        stroke = QtGui.QPainterPathStroker()
        stroke.setWidth(10)
        self.setPath(stroke.createStroke(path))
        self._end_pos = p

    def paint(self, painter, option, widget):
        option.state &= ~QtWidgets.QStyle.State_Selected
        super().paint(painter, option, widget)

    def itemChange(self, change, value):
        if change == QtWidgets.QGraphicsItem.ItemSceneHasChanged:
            if self.scene():
                self.scene().addItem(self.handle)
        elif change == QtWidgets.QGraphicsItem.ItemPositionChange and self.isEnabled():
            p = self.mapToScene(self.end_pos)
            self.handle.setPos(p)
        return super().itemChange(change, value)


if __name__ == "__main__":
    app = QtWidgets.QApplication(sys.argv)
    scene = QtWidgets.QGraphicsScene(sceneRect=QtCore.QRectF(0, 0, 200, 200))
    item = PipeItem()
    scene.addItem(item)
    view = QtWidgets.QGraphicsView(scene)
    window = QtWidgets.QMainWindow()
    window.setCentralWidget(view)
    window.resize(640, 480)
    window.show()
    sys.exit(app.exec_())

UPDATE:

如果你想要实现你想要的逻辑，那就更复杂了。错误的原因是paint()方法使用boundingRect()来设置油漆区域，但在你的情况下，它没有考虑到它的变化，一个可能的解决方案是以下。

class Item(QGraphicsPathItem):
    circle = QPainterPath()
    circle.addEllipse(QRectF(-5, -5, 10, 10))

    # ...

    def boundingRect(self):
        return self.shape().boundingRect()