如何在 QGraphicsview 内连续绘制透明线而不重叠？

问题描述

我正在尝试以两种方式绘制由线条组成的路径： 首先，路径由直线组成，它们的端点是相同的。使用这种方法的问题在于线条在其末端重叠，导致不良影响，如下图所示：

这是代码：

from PyQt5 import QtWidgets,QtCore,QtGui
import typing
import random


class Track(QtWidgets.QGraphicsPathItem):
    def __init__(self,parent=None,offset: float = 50):
        super(Track,self).__init__(parent)  # initiate the parent class
        self.__points: list = [QtCore.QPointF(0,0)]
        self.__pen: QtGui.QPen = QtGui.QPen()
        self.setPen()

    def getPoints(self) -> list:
        return self.__points

    def append(self,point: QtCore.QPointF):
        self.__points.append(point)

    def getPen(self) -> QtGui.QPen:
        return self.__pen

    def setPen(self,pen: QtGui.QPen = None,width: int = 10,color: QtGui.QColor = QtGui.QColor(0,24,128,100),cap: QtCore.Qt.PenCapStyle = QtCore.Qt.SquareCap,line_style: QtCore.Qt.PenStyle = QtCore.Qt.solidLine,join: QtCore.Qt.PenJoinStyle = QtCore.Qt.RoundJoin) -> None:
        """
        Set the pen that will be used to paint the implement.
        :param pen : set the pen or its arguments
        :param width: the pen width.
        :param color: the pen color.
        :param cap: the cap style: rounded,flatted and squared.
        :param line_style: dashed,solid ...
        :param join: miter,rounded ...
        :return: None
        """
        if pen == None:
            self.__pen.setWidth(width)  # set the pen width
            self.__pen.setColor(color)  # define your color from QtCore,it is safer to use the statement:
            self.__pen.setCapStyle(cap)  # set the cap style of the line
            self.__pen.setStyle(line_style)  # set the line style for instance: solid,dash... whatever
            self.__pen.setJoinStyle(join)  # set how the lines will be connected.
        else:
            self.__pen = pen

    def paint(self,painter: QtGui.QPainter,option: QtWidgets.qstyleOptionGraphicsItem,widget: typing.Optional[QtWidgets.QWidget] = ...) -> None:
        painter.setPen(self.getPen())
        painter.setRenderHint(QtGui.QPainter.HighQualityAntialiasing)

        try:
            path = QtGui.QPainterPath()
            path.moveto(self.getPoints()[0])
            for point in self.getPoints():
                path.lineto(point)
            painter.drawPath(path)
        except IndexError:
            self.append(QtCore.QPointF(0,0))


class Producer(QtCore.QObject):

    def __init__(self,parent=None):
        super(Producer,self).__init__(parent)
        self.__last_point = QtCore.QPointF(10,0)
        self.__point = QtCore.QPointF(10,0)
        self.upper = 10
        self.bottom = 0

    def setPoint(self) -> None:
        self.setLastpoint(self.getPoint())
        x = random.randint(self.bottom,self.upper)
        y = random.randint(self.bottom,self.upper)
        self.upper += 50  # increases the range of probability at the upper limit
        self.__point = QtCore.QPointF(x,y)  # produce a new random point

    def getPoint(self) -> QtCore.QPointF:
        return self.__point

    def setLastpoint(self,point: QtCore.QPointF):
        self.__last_point = point

    def getLastPoint(self) -> QtCore.QPointF:
        return self.__last_point



class Window2(QtWidgets.QMainWindow):
    def __init__(self):
        super(Window2,self).__init__()
        central_widget = QtWidgets.QWidget()
        self.__pen = QtGui.QPen()
        self.setMinimumHeight(500)
        self.setMinimumWidth(500)
        self.scene = QtWidgets.QGraphicsScene(self)
        self.view = QtWidgets.QGraphicsView(self.scene)
        self.view.setSceneRect(self.view.mapToScene(self.view.viewport().rect()).boundingRect())
        self.btn = QtWidgets.QPushButton('Get Track')
        self.btn.clicked.connect(self.getTrack)
        self.producer = Producer()
        hBox = QtWidgets.QHBoxLayout(central_widget)
        hBox.addWidget(self.view)
        hBox.addWidget(self.btn)
        self.setCentralWidget(central_widget)
        self.setPen()

    def getPen(self) -> QtGui.QPen:
        return self.__pen

    def getTrack(self):
        print('run')
        self.producer.setPoint()
        line = QtCore.QLineF(self.producer.getPoint(),self.producer.getLastPoint())
        self.scene.addLine(line,pen = self.getPen())
        dx = self.producer.getPoint().x() - self.producer.getLastPoint().x()
        dy = self.producer.getPoint().y() - self.producer.getLastPoint().y()
        print(dx,dy)
        self.view.setSceneRect(self.view.sceneRect().translated(dx,dy))

    def setPen(self,dash... whatever
            self.__pen.setJoinStyle(join)  # set how the lines will be connected.
        else:
            self.__pen = pen


if __name__ == "__main__":
    import sys

    app = QtWidgets.QApplication(sys.argv)
    # w = Window()
    w = Window2()
    w.show()
    sys.exit(app.exec_())

我使用的第二种方法是创建一条由点组成的连续路径。此路径继承类：QGraphicsPathItem。但是，当我“更新”我的“场景矩形”时，这条路径在它的一端在我的边界之外时消失了 =“场景矩形”。有什么办法可以防止它消失吗？ 我正在采用的这种方法的第二个问题是，我需要保存构成我的路径的这些点......对于少量点，这不是问题，但是当我的路径充满点时，它将有内存管理问题。图片：

代码在这里：

class Window(QtWidgets.QMainWindow):
    def __init__(self):
        super(Window,self).__init__()
        central_widget = QtWidgets.QWidget()
        self.setMinimumHeight(500)
        self.setMinimumWidth(500)
        self.scene = QtWidgets.QGraphicsScene(self)
        self.view = QtWidgets.QGraphicsView(self.scene)
        self.view.setSceneRect(self.view.mapToScene(self.view.viewport().rect()).boundingRect())
        self.btn = QtWidgets.QPushButton('Get Track')
        self.btn.clicked.connect(self.getTrack)
        self.producer = Producer()
        hBox = QtWidgets.QHBoxLayout(central_widget)
        hBox.addWidget(self.view)
        hBox.addWidget(self.btn)
        self.track = Track()
        self.scene.addItem(self.track)
        self.setCentralWidget(central_widget)

    def getTrack(self):
        self.producer.setPoint()
        self.track.append(self.producer.getPoint())
        dx = self.producer.getPoint().x() - self.producer.getLastPoint().x()
        dy = self.producer.getPoint().y() - self.producer.getLastPoint().y()
        print(dx,dy))

我正在尝试模拟 GPS，我正在绘制的路径是 汽车的排量。但我不知道这两种方法哪个更好，是否还有另一种。

这里有一个最小的可重现示例：

from PyQt5 import QtWidgets,QtGui
import typing
import random

pen = QtGui.QPen()
pen.setColor(QtGui.QColor(0,100))
pen.setWidth(10)
pen.setStyle(QtCore.Qt.solidLine)

pen.setCapStyle(QtCore.Qt.SquareCap)


class Track(QtWidgets.QGraphicsPathItem):
    def __init__(self,0)]

    def getPoints(self) -> list:
        return self.__points

    def append(self,point: QtCore.QPointF):
        self.__points.append(point)

    def paint(self,widget: typing.Optional[QtWidgets.QWidget] = ...) -> None:
        painter.setPen(pen)
        painter.setRenderHint(QtGui.QPainter.HighQualityAntialiasing)
        path = QtGui.QPainterPath()
        path.moveto(self.getPoints()[0])
        for point in self.getPoints():
            path.lineto(point)
        painter.drawPath(path)

class Producer(QtCore.QObject):

    def __init__(self,0)
        self.upper = 10

    def setPoint(self) -> None:
        self.setLastpoint(self.getPoint())
        x = random.randint(0,self.upper)
        y = random.randint(0,point: QtCore.QPointF):
        self.__last_point = point

    def getLastPoint(self) -> QtCore.QPointF:
        return self.__last_point


class Window(QtWidgets.QMainWindow):
    def __init__(self):
        super(Window,self).__init__()
        central_widget = QtWidgets.QWidget()
        self.setMinimumHeight(500)
        self.setMinimumWidth(500)
        self.scene = QtWidgets.QGraphicsScene(self)
        self.view = QtWidgets.QGraphicsView(self.scene)
        self.view.setSceneRect(self.view.mapToScene(self.view.viewport().rect()).boundingRect())
        self.btn = QtWidgets.QPushButton('Get Track')
        self.btn.clicked.connect(self.getTrack)
        self.producer = Producer()
        hBox = QtWidgets.QHBoxLayout(central_widget)
        hBox.addWidget(self.view)
        hBox.addWidget(self.btn)
        self.track = Track()
        self.scene.addItem(self.track)
        self.setCentralWidget(central_widget)

    def getTrack(self):
        self.producer.setPoint()
        self.track.append(self.producer.getPoint())
        dx = self.producer.getPoint().x() - self.producer.getLastPoint().x()
        dy = self.producer.getPoint().y() - self.producer.getLastPoint().y()
        self.view.setSceneRect(self.view.sceneRect().translated(dx,dy))


class Window2(QtWidgets.QMainWindow):
    def __init__(self):
        super(Window2,self).__init__()
        central_widget = QtWidgets.QWidget()
        self.setMinimumHeight(500)
        self.setMinimumWidth(500)
        self.scene = QtWidgets.QGraphicsScene(self)
        self.view = QtWidgets.QGraphicsView(self.scene)
        self.view.setSceneRect(self.view.mapToScene(self.view.viewport().rect()).boundingRect())
        self.btn = QtWidgets.QPushButton('Get Track')
        self.btn.clicked.connect(self.getTrack)
        self.producer = Producer()
        hBox = QtWidgets.QHBoxLayout(central_widget)
        hBox.addWidget(self.view)
        hBox.addWidget(self.btn)
        self.setCentralWidget(central_widget)

    def getTrack(self):
        self.producer.setPoint()
        self.scene.addLine(QtCore.QLineF(self.producer.getPoint(),self.producer.getLastPoint()),pen=pen)
        dx = self.producer.getPoint().x() - self.producer.getLastPoint().x()
        dy = self.producer.getPoint().y() - self.producer.getLastPoint().y()
        self.view.setSceneRect(self.view.sceneRect().translated(dx,dy))


if __name__ == "__main__":
    import sys

    app = QtWidgets.QApplication(sys.argv)
    # w = Window()
    w = Window2()
    w.show()
    sys.exit(app.exec_())

解决方法

使用多个线段显然不是正确的选择，因为线被认为是单独的元素，如果没有折叠的边缘，就不可能绘制它们。

关于 QPainterPath 方法的最重要的问题是，当您使用 QGraphicsPathItem 时，您根本不使用它，因为您覆盖了它的 paint() 方法。
手动绘制路径使其完全无用，您应该改用它的 setPath()。

你的实现也是错误的，因为它没有考虑路径的其余部分，并且使用增量翻译。正如在对您的另一个问题的评论中已经建议的那样，增量转换通常不是一个好主意，因为它们通常具有误导性，并且通常会导致意外行为（就像在这种情况下一样）。

解决方案是正确使用 QGraphicsPathItem：

class Track(QtWidgets.QGraphicsPathItem):
    def __init__(self,parent=None,offset: float = 50):
        super(Track,self).__init__(parent)  # initiate the parent class
        self.__points = [QtCore.QPointF(0,0)]
        self.setPen(pen)

    def getPoints(self) -> list:
        return self.__points

    def append(self,point: QtCore.QPointF):
        self.__points.append(point)
        path = self.path()
        path.lineTo(point)
        self.setPath(path)

    # no paint method override!

然后，为了保证item始终可见，可以使用现有的ensureVisible(item)或者centerOn(item)方法；请注意，我还删除了第一个 setSceneRect() 调用，这是因为将其保留为默认值可确保视图的 sceneRect 始终更新为场景的 sceneRect，默认为项目的class Window(QtWidgets.QMainWindow): def __init__(self): # ... # remove the following! # self.view.setSceneRect(self.view.mapToScene(self.view.viewport().rect()).boundingRect()) # set the antialiasing for the whole view self.view.setRenderHints(QtGui.QPainter.HighQualityAntialiasing) def getTrack(self): self.producer.setPoint() self.track.append(self.producer.getPoint()) self.view.centerOn(self.track) # no setSceneRect() even here 除非明确指定，否则边界矩形：

paint()

最后，您真的不应该太在意内存使用情况。 QPoints 的内存占用非常小，如果您担心系统无法支持它，那么您就偏离了轨道：您需要大约 20 000 个积分才能获得一个积分兆字节内存。

^{注意与问题无关：我会避免不必要的过度使用类型提示。 Python 将始终是一种动态类型语言，虽然使用它们不被认为是不好的做法，但过多地使用它们只会分散注意力，尤其是在处理库/框架内部使用的覆盖方法时；例如，完全不需要 *=*gpu 中的类型提示，因为您可以确定所有参数将始终使用正确的类型调用}