如何翻译/拖动/移动QGraphicsScene？

Question

我知道这个问题已经回答了很多次，尤其是在Qt的C ++版本中，但是我在C ++中不太好，找不到解决方案。

我有一个代码，其中QGraphicsView的矩形由中心的QGraphicsPolygonItem组成。我试图找到一种方法使用户可以翻译/移动/拖动QGraphicsScene（一切都可以，我只是想给用户一个在场景中移动的选项）。但我的尝试都无济于事。

我尝试设置：

• [self.horizontalScrollBar().setValue()和self.verticalScrollBar().setValue()

• self._scene.setSceneRect(x,y,w,h)

• 将锚设置为AnchorUnderMouse和NoAnchor

• 使用translate()

[没有一个使我的场景移动...唯一使我的场景移动的东西是setSceneRect()，但是一旦将它放在mouseMoveEvent(self,event)下，它就会停止工作。有人可以帮助我学习如何在场景中到处移动该矩形吗？

代码：

from PyQt5.QtGui import QColor, QPolygonF, QPen, QBrush
from PyQt5.QtCore import Qt, QPointF, QPoint, pyqtSignal
from PyQt5.QtWidgets import QDialog, QVBoxLayout, QGraphicsView, QGraphicsScene, QGraphicsPolygonItem, QApplication, \
    QFrame, QSizePolicy

points_list = [[60.1, 19.6, 0.0], [60.1, 6.5, 0.0], [60.1, -6.5, 0.0], [60.1, -19.6, 0.0], [60.1, -19.6, 0.0],
               [20.0, -19.6, 0.0], [-20, -19.6, 0.0], [-60.1, -19.6, 0.0], [-60.1, -19.6, 0.0], [-60.1, -6.5, 0.0],
               [-60.1, 6.5, 0.0], [-60.1, 19.6, 0.0], [-60.1, 19.6, 0.0], [-20.0, 19.6, 0.0], [20.0, 19.6, 0.0],
               [60.1, 19.6, 0.0]]


class MainWindow(QDialog):
    def __init__(self, parent=None):
        QDialog.__init__(self, parent=parent)
        self.create()

    def create(self, **kwargs):
        main_layout = QVBoxLayout()
        graphics = MainGraphicsWidget()
        main_layout.addWidget(graphics)
        self.setLayout(main_layout)

class MainGraphicsWidget(QGraphicsView):
    zoom_signal = pyqtSignal(bool)

    def __init__(self, parent=None):
        super(MainGraphicsWidget, self).__init__(parent)
        self._scene = QGraphicsScene(backgroundBrush=Qt.gray)
        self.__zoom = 0
        self.setScene(self._scene)
        self.setTransformationAnchor(QGraphicsView.NoAnchor)
        #self.setTransformationAnchor(QGraphicsView.AnchorUnderMouse)
        self.setResizeAnchor(QGraphicsView.AnchorUnderMouse)
        self.setVerticalScrollBarPolicy(Qt.ScrollBarAlwaysOff)
        self.setHorizontalScrollBarPolicy(Qt.ScrollBarAlwaysOff)
        self.setBackgroundBrush(QBrush(QColor(30, 30, 30)))
        self.setFrameShape(QFrame.NoFrame)
        self.setSizePolicy(QSizePolicy(QSizePolicy.Expanding, QSizePolicy.Expanding))
        self.sceneRect = self._scene.sceneRect()
        self.testButton = GraphicsButton()
        self._scene.addItem(self.testButton)
        #self.horizontalScrollBar().setValue(199)
        #self.verticalScrollBar().setValue(500)

    def mouseMoveEvent(self, event):
        modifierPressed = QApplication.keyboardModifiers()
        if (modifierPressed & Qt.AltModifier) == Qt.AltModifier and event.buttons() == Qt.LeftButton:
            #self._scene.setSceneRect(event.pos().x(), event.pos().y(), self.sceneRect.width(), self.sceneRect.height())
            pass

        super(MainGraphicsWidget, self).mouseMoveEvent(event)

    def wheelEvent(self, event):
        if event.angleDelta().y() > 0:
            factor = 1.25
            self.__zoom += 1
        else:
            factor = 0.8
            self.__zoom -= 1
        self.scale(factor, factor)
        self.zoom_signal.emit(self.__zoom < 10)


class GraphicsButton(QGraphicsPolygonItem):
    def __init__(self, parent=None):
        super(GraphicsButton, self).__init__(parent)
        self.myPolygon = QPolygonF([QPointF(v1, v2) for v1, v2, v3 in points_list])
        self.setPen(QPen(QColor(0, 0, 0), 0, Qt.SolidLine, Qt.FlatCap, Qt.MiterJoin))
        self.setPolygon(self.myPolygon)
        self.setBrush(QColor(220, 40, 30))


if __name__ == '__main__':
    import sys
    app = QApplication(sys.argv)
    window = MainWindow()
    window.setGeometry(500, 100, 500, 900)
    window.show()
    sys.exit(app.exec_())

Answer 1

您的方法行不通，因为您一直在用event.pos()坐标不断“转换” sceneRect的原点，并且由于这些值始终为正，因此您“聚焦”在一个显然在相反的方向。例如，如果拖动鼠标在右侧移动，就像在右侧移动照相机：图片的内容将在左侧“移动”。

虽然使用负x和y位置将是最合乎逻辑的解决方案，但是对于实际的“拖动”操作而言，它是无效的，因为坐标是基于小部件的；如果从原点（窗口小部件的左上角）拖远，则平移会更大：如果从视图中心开始拖移，则场景矩形将水平平移250个像素，垂直平移450个像素（因为您的窗口大小是500x900）。

最佳方法是跟踪先前的鼠标位置（从鼠标按下事件开始），并根据mouseMoveEvent位置之间的差异来平移场景。由于可能会对场景应用某些缩放比例（当您使用滚轮进行缩放时），因此我们也必须考虑这些比例。

class MainGraphicsWidget(QGraphicsView):
    zoom_signal = pyqtSignal(bool)

    def __init__(self, parent=None):
        super(MainGraphicsWidget, self).__init__(parent)
        # ...
        # I'm commenting this line, as sceneRect is a property of QGraphicsView
        # and should not be overwritten
        # self.sceneRect = self._scene.sceneRect()
        self.testButton = GraphicsButton()
        self._scene.addItem(self.testButton)
        self.startPos = None


    def mousePressEvent(self, event):
        if event.modifiers() & Qt.ControlModifier and event.button() == Qt.LeftButton:
            # store the origin point
            self.startPos = event.pos()
        else:
            super(MainGraphicsWidget, self).mousePressEvent(event)

    def mouseMoveEvent(self, event):
        if self.startPos is not None:
            # compute the difference between the current cursor position and the
            # previous saved origin point
            delta = self.startPos - event.pos()
            # get the current transformation (which is a matrix that includes the
            # scaling ratios
            transform = self.transform()
            # m11 refers to the horizontal scale, m22 to the vertical scale;
            # divide the delta by their corresponding ratio
            deltaX = delta.x() / transform.m11()
            deltaY = delta.y() / transform.m22()
            # translate the current sceneRect by the delta
            self.setSceneRect(self.sceneRect().translated(deltaX, deltaY))
            # update the new origin point to the current position
            self.startPos = event.pos()
        else:
            super(MainGraphicsWidget, self).mouseMoveEvent(event)

    def mouseReleaseEvent(self, event):
        self.startPos = None
        super(MainGraphicsWidget, self).mouseReleaseEvent(event)

请注意，我使用ControlModifier，因为在Linux上Alt修饰符通常用于移动窗口。