似乎不可能使用 QPainter （或任何其他方法）旋转自定义 QGraphicsItem 。

Question

这里是代码。它运行。展示这个错误。右键单击椭圆，通过在椭圆上单击拖动来缩放它。右键单击它>“完成编辑”。然后用“旋转”做同样的事情。

我已经尝试了超过 10 种使用 self.setRotation、self.setTransform、painter.rotate 等的不同排列方式......它唯一一次旋转是在我使用 self.setTransform(self.transform().rotate(r)) 时，但结果是错误的：以错误的顺序缩放和旋转或其他东西。

from PyQt5.QtWidgets import QGraphicsItem, QMenu
from PyQt5.QtGui import QTransform, QPen, QPainter, QColor, QBrush
from PyQt5.QtCore import Qt, QPointF, QRectF, QEvent
from math import sqrt


def scaleRect(rect, scale_x, scale_y):
    T = QTransform.fromScale(scale_x, scale_y)
    return T.mapRect(rect)

def debugPrintTransformMatrix(T):
    print(str(T.m11()) + '  ' + str(T.m12()) + '  ' + str(T.m13()))
    print(str(T.m21()) + '  ' + str(T.m22()) + '  ' + str(T.m23()))
    print(str(T.m31()) + '  ' + str(T.m32()) + '  ' + str(T.m33()))

# Assumes no shearing or stretching.   
# Only Rotation, Translation, and Scaling. 
def extractTransformScale(T):
    # This is math matrix notation transposed (debug print self.sceneTransform() to see)
    Sx = sqrt(T.m11()**2 + T.m12()**2)      
    Sy = sqrt(T.m21()**2 + T.m22()**2)
    return Sx, Sy    

def extractTransformTranslate(T):
    return T.m31(), T.m32()


class Object(QGraphicsItem):
    def sceneEvent(self, event):
        if event.type() == QEvent.GraphicsSceneMouseMove: 
            # move, scale, or rotate
            if self._mode in ['scale', 'rotate']:
                mouse_pos = event.scenePos()
                last_pos = event.lastScenePos()
                if self._mode == 'scale':
                    s = self.mouseScalingFactors(mouse_pos, last_pos)
                    self.setTransform(self.transform().scale(*s))
                if self._mode == 'rotate':
                    r = self.mouseRotationAngle(mouse_pos, last_pos)
                    self.setRotation(self.rotation() + r)
                return True

        return super().sceneEvent(event)

    def __init__(self):
        super().__init__()
        self.setFlags(QGraphicsItem.ItemIsMovable | QGraphicsItem.ItemIsFocusable | QGraphicsItem.ItemIsSelectable)
        self._selectionPen = QPen(Qt.black, 1.0, style=Qt.DotLine, cap=Qt.FlatCap)
        self._lastPos = QPointF(0, 0)
        self.setPos(self._lastPos)
        self._mode = 'neutral'

    def setRenderHints(self, painter):
        painter.setRenderHints(QPainter.SmoothPixmapTransform | QPainter.HighQualityAntialiasing | QPainter.TextAntialiasing)

    def boundingRectExtraScale(self):
        return (1.2 , 1.2) 

    def mouseScalingFactors(self, pos, last_pos):
        delta = pos - last_pos
        return (1.01 ** delta.x(), 1.01 ** delta.y())

    def mouseRotationAngle(self, pos, last_pos):
        return 1   #TODO

    def createDefaultContextMenu(self):
        menu = QMenu()
        if self._mode == 'neutral':
            menu.addAction('Scale').triggered.connect(lambda: self.setMode('scale'))
            menu.addAction('Rotate').triggered.connect(lambda: self.setMode('rotate'))
        else:
            menu.addAction('Done Editing').triggered.connect(lambda: self.setMode('neutral'))
        return menu

    def contextMenuEvent(self, event):
            menu = self.createDefaultContextMenu()
            menu.exec(event.screenPos())

    def setMode(self, mode):
        self._mode = mode

    def setSelected(self, selected):
        super().setSelected(selected)
        self.update()


class ShapedObject(Object):
    def __init__(self):
        super().__init__()
        self._shape = {
            'name' : 'ellipse',
            'radius': 35
        }
        self._brush = QBrush(Qt.darkGreen)
        self._pen = QPen(Qt.yellow, 3)        

    def shapeDef(self):
        return self._shape

    def boundingRect(self):
        rect = self.shapeRect()
        s = self.boundingRectExtraScale()
        return scaleRect(rect, *s)

    def shape(self):      #TODO QPainterPath shape for collision detection
        # Should call self.boundingRectExtraScale()
        return super().shape()

    def paint(self, painter, option, widget):
        self.setRenderHints(painter)
        #super().paint(painter, option, widget)

        shape = self.shapeDef()
        name = shape['name']

        painter.setBrush(self._brush)
        painter.setPen(self._pen)

        painter.save()

        # ********** HERE IS THE PROBLEM ************* 

        debugPrintTransformMatrix(painter.transform())
        painter.rotate(5)
        debugPrintTransformMatrix(painter.transform())

        rect = self.shapeRect()
        if name == 'ellipse':
            painter.drawEllipse(rect)


        painter.restore()  


    def shapeRect(self):
        shape = self.shapeDef()
        name = shape['name']
        if name == 'ellipse':
            r = shape['radius']
            rect = QRectF(-r,  -r, 2*r, 2*r)
        return rect


####

import sys
from PyQt5.QtWidgets import QMainWindow, QGraphicsScene, QGraphicsView, QApplication

if __name__ == '__main__':
    app = QApplication(sys.argv)

    window = QMainWindow()
    view = QGraphicsView()
    scene = QGraphicsScene()
    view.setScene(scene)
    window.setCentralWidget(view)

    ellipse = ShapedObject()
    scene.addItem(ellipse)

    window.show()

    sys.exit(app.exec_())

Answer 1

让它工作。这是操作旋转/缩放的顺序。永远不要用圆圈来测试你的旋转代码，哈哈！

from PyQt5.QtWidgets import QGraphicsItem, QMenu, QGraphicsRotation, QGraphicsScale
from PyQt5.QtGui import QTransform, QPen, QPainter, QColor, QBrush, QPainterPath
from PyQt5.QtCore import Qt, QPointF, QRectF, QEvent
from math import sqrt


def scaleRect(rect, scale_x, scale_y):
    T = QTransform.fromScale(scale_x, scale_y)
    return T.mapRect(rect)

def debugPrintTransformMatrix(T):
    print(str(T.m11()) + '  ' + str(T.m12()) + '  ' + str(T.m13()))
    print(str(T.m21()) + '  ' + str(T.m22()) + '  ' + str(T.m23()))
    print(str(T.m31()) + '  ' + str(T.m32()) + '  ' + str(T.m33()))

# Assumes no shearing or stretching.   
# Only Rotation, Translation, and Scaling. 
def extractTransformScale(T):
    # This is math matrix notation transposed (debug print self.sceneTransform() to see)
    Sx = sqrt(T.m11()**2 + T.m12()**2)      
    Sy = sqrt(T.m21()**2 + T.m22()**2)
    return Sx, Sy    

def extractTransformTranslate(T):
    return T.m31(), T.m32()


class Object(QGraphicsItem):
    def sceneEvent(self, event):
        if event.type() == QEvent.GraphicsSceneMouseMove: 
            # move, scale, or rotate
            if self._mode in ['scale', 'rotate']:
                mouse_pos = event.scenePos()
                last_pos = event.lastScenePos()
                if self._mode == 'scale':
                    s = self.mouseScalingFactors(mouse_pos, last_pos)
                    self.applyScaleTransform(*s)
                if self._mode == 'rotate':
                    r = self.mouseRotationAngle(mouse_pos, last_pos)
                    self.applyRotateTransform(r)
                return True

        return super().sceneEvent(event)

    def __init__(self):
        super().__init__()
        self.setFlags(QGraphicsItem.ItemIsMovable | QGraphicsItem.ItemIsFocusable | QGraphicsItem.ItemIsSelectable)
        self._selectionPen = QPen(Qt.black, 1.0, style=Qt.DotLine, cap=Qt.FlatCap)
        self._lastPos = QPointF(0, 0)
        self.setPos(self._lastPos)
        self._mode = 'neutral'
        self._scale = QGraphicsScale()
        self._rotate = QGraphicsRotation()
        self.setTransformations([self._rotate, self._scale])

    def applyRotateTransform(self, angle):
        self._rotate.setAngle(self._rotate.angle() + 15)

    def applyScaleTransform(self, sx, sy):
        self._scale.setXScale(sx * self._scale.xScale())
        self._scale.setYScale(sy * self._scale.yScale())

    def setRenderHints(self, painter):
        painter.setRenderHints(QPainter.SmoothPixmapTransform | QPainter.HighQualityAntialiasing | QPainter.TextAntialiasing)

    def boundingRectExtraScale(self):
        return (1.2 , 1.2) 

    def mouseScalingFactors(self, pos, last_pos):
        delta = pos - last_pos
        return (1.01 ** delta.x(), 1.01 ** delta.y())

    def mouseRotationAngle(self, pos, last_pos):
        return 1   #TODO

    def createDefaultContextMenu(self):
        menu = QMenu()
        if self._mode == 'neutral':
            menu.addAction('Scale').triggered.connect(lambda: self.setMode('scale'))
            menu.addAction('Rotate').triggered.connect(lambda: self.setMode('rotate'))
        else:
            menu.addAction('Done Editing').triggered.connect(lambda: self.setMode('neutral'))
        return menu

    def contextMenuEvent(self, event):
            menu = self.createDefaultContextMenu()
            menu.exec(event.screenPos())

    def setMode(self, mode):
        self._mode = mode

    def setSelected(self, selected):
        super().setSelected(selected)
        self.update()


class ShapedObject(Object):
    def __init__(self):
        super().__init__()
        self._shape = {
            'name' : 'ellipse',
            'radius': 35
        }
        self._brush = QBrush(Qt.darkGreen)
        self._pen = QPen(Qt.yellow, 3)        

    def shapeDef(self):
        return self._shape

    def boundingRect(self):
        rect = self.shapeRect()
        s = self.boundingRectExtraScale()
        return scaleRect(rect, *s)

    def shape(self):      #TODO QPainterPath shape for collision detection
        # Should call self.boundingRectExtraScale()
        return super().shape()

    def paint(self, painter, option, widget):
        self.setRenderHints(painter)
        #super().paint(painter, option, widget)

        shape = self.shapeDef()
        name = shape['name']

        painter.setBrush(self._brush)
        painter.setPen(self._pen)

        painter.save()
        path = QPainterPath()

        if name == 'ellipse':
            r = shape['radius']
            path.addEllipse(QPointF(0, 0), r, r)

        painter.drawPath(path)
        painter.restore()  

    def shapeRect(self):
        shape = self.shapeDef()
        name = shape['name']
        if name == 'ellipse':
            r = shape['radius']
            rect = QRectF(-r,  -r, 2*r, 2*r)
        return rect


####

import sys
from PyQt5.QtWidgets import QMainWindow, QGraphicsScene, QGraphicsView, QApplication

if __name__ == '__main__':
    app = QApplication(sys.argv)

    window = QMainWindow()
    view = QGraphicsView()
    scene = QGraphicsScene()
    view.setScene(scene)
    window.setCentralWidget(view)

    ellipse = ShapedObject()
    scene.addItem(ellipse)

    window.show()

    sys.exit(app.exec_())