如何使用 Python 中的 Qt "Graphics View"框架？

Question

背景：我正在尝试使用QT图形视图框架在Python中进行VR演示，该框架允许自定义渲染的GUI。我可以选择包含QT：PyQt5和PySide2的两个不同的Python模块。不幸的是，这些模块中的每一个似乎都缺少图形视图框架中的另一个关键成分。

PyQt5似乎缺少QGraphicsSceneMouseEvent的构造函数，这是从VR控制器手势中创建合成鼠标事件所需的。这个简短的pyqt5程序...

from PyQt5.QtCore import QEvent, QPointF, Qt
from PyQt5.QtGui import QMouseEvent
from PyQt5.QtWidgets import QGraphicsSceneMouseEvent
from PyQt5.QtGui import QOpenGLPaintDevice  # No problem for PyQt5
pos = QPointF(20, 20)
event1 = QMouseEvent(QEvent.MouseMove, pos, Qt.LeftButton, Qt.LeftButton, Qt.NoModifier)
device = QOpenGLPaintDevice(100, 100)
# Problem: TypeError: PyQt5.QtWidgets.QGraphicsSceneMouseEvent cannot be instantiated or sub-classed
event2 = QGraphicsSceneMouseEvent(QEvent.GraphicsSceneMouseMove)

...导致TypeError: PyQt5.QtWidgets.QGraphicsSceneMouseEvent cannot be instantiated or sub-classed

看似好消息是，替代QT结合PySide2模块可以毫无抱怨地构建QGraphicsSceneMouseEvent。但是PySide2缺少Qopenglpaintdevice类，我需要实际绘制小部件。这个非常相似的程序，使用Pyside2 ...

from PySide2.QtCore import QEvent, QPointF, Qt
from PySide2.QtGui import QMouseEvent
from PySide2.QtWidgets import QGraphicsSceneMouseEvent
pos = QPointF(20, 20)
event1 = QMouseEvent(QEvent.MouseMove, pos, Qt.LeftButton, Qt.LeftButton, Qt.NoModifier)
event2 = QGraphicsSceneMouseEvent(QEvent.GraphicsSceneMouseMove)  # No Problem for PySide2
from PySide2.QtGui import QOpenGLPaintDevice  # Problem: PySide2 does not have this class
device = QOpenGLPaintDevice(100, 100)

导致ImportError: cannot import name 'QOpenGLPaintDevice'

我不确定有人是否曾经成功使用过Python的QT图形视图框架。如果没有，我想成为第一个。

Answer 1

在我看来，在pyqt5中未启用qgraphicsscenemouseevent并不是一个错误没有公共构造函数。

如果要在QT图形框架中模拟鼠标运动，则必须将qmouseevent发送到qgraphicsView的viewport()。

在下面的示例中，我通过使用qmouseeevent模拟鼠标来显示如何移动项目：

from functools import partial
from PySide2 import QtCore, QtGui, QtWidgets
# from PyQt5 import QtCore, QtGui, QtWidgets

class MainWindow(QtWidgets.QMainWindow):
    def __init__(self, parent=None):
        super(MainWindow, self).__init__(parent)
        self.m_scene = QtWidgets.QGraphicsScene(QtCore.QRectF(0, 0, 400, 400), self)
        self.m_graphicsview = QtWidgets.QGraphicsView(self.m_scene)
        self.setCentralWidget(self.m_graphicsview)
        self.resize(640, 480)
        self.m_item = QtWidgets.QGraphicsRectItem(QtCore.QRectF(-50, -50, 100, 100))
        self.m_item.setFlags(
            self.m_item.flags() | QtWidgets.QGraphicsItem.ItemIsMovable
        )
        self.m_item.setBrush(QtGui.QColor("salmon"))
        self.m_item.setPos(100, 100)
        self.m_scene.addItem(self.m_item)
        QtCore.QTimer.singleShot(1000, self.emulate_move_item)
    def emulate_move_item(self):
        sp = self.m_item.mapToScene(self.m_item.boundingRect().center())
        lp = self.m_graphicsview.mapFromScene(sp)
        end_pos = lp + QtCore.QPoint(100, 100)
        self.press(lp)
        animation = QtCore.QVariantAnimation(
            self,
            startValue=lp,
            endValue=end_pos
        )
        animation.valueChanged.connect(self.moveTo)
        animation.finished.connect(partial(self.release, end_pos))
        animation.start(QtCore.QAbstractAnimation.DeleteWhenStopped)
    def press(self, pos):
        event = QtGui.QMouseEvent(
            QtCore.QEvent.MouseButtonPress,
            pos,
            self.m_graphicsview.mapToGlobal(pos),
            QtCore.Qt.LeftButton,
            QtCore.Qt.LeftButton,
            QtCore.Qt.NoModifier,
        )
        QtCore.QCoreApplication.postEvent(self.m_graphicsview.viewport(), event)
    def moveTo(self, pos):
        event = QtGui.QMouseEvent(
            QtCore.QEvent.MouseMove,
            pos,
            self.m_graphicsview.viewport().mapToGlobal(pos),
            QtCore.Qt.LeftButton,
            QtCore.Qt.LeftButton,
            QtCore.Qt.NoModifier,
        )
        QtCore.QCoreApplication.postEvent(self.m_graphicsview.viewport(), event)
    def release(self, pos):
        event = QtGui.QMouseEvent(
            QtCore.QEvent.MouseButtonRelease,
            pos,
            self.m_graphicsview.viewport().mapToGlobal(pos),
            QtCore.Qt.LeftButton,
            QtCore.Qt.LeftButton,
            QtCore.Qt.NoModifier,
        )
        QtCore.QCoreApplication.postEvent(self.m_graphicsview.viewport(), event)
    def double_click(self, pos):
        event = QtGui.QMouseEvent(
            QtCore.QEvent.MouseButtonDblClick,
            pos,
            self.m_graphicsview.viewport().mapToGlobal(pos),
            QtCore.Qt.LeftButton,
            QtCore.Qt.LeftButton,
            QtCore.Qt.NoModifier,
        )
        QtCore.QCoreApplication.postEvent(self.m_graphicsview.viewport(), event)

if __name__ == "__main__":
    import sys
    app = QtWidgets.QApplication(sys.argv)
    w = MainWindow()
    w.show()
    sys.exit(app.exec_())

结论：

• 不得在Python中启用QGraphicsSceneMouseEvent构造函数，因为在C 的QT公共API中无法访问它。因此，pyqt5的行为是正确的，但是pyside2有一个错误。

• Pyside2没有实现Qopenglpaintdevice类是一个可能的错误。