PyQt QGraphicsView 使用变换矩阵进行平移和缩放

Question

我正在尝试使用 QGraphics 变换矩阵进行平移和缩放。缩放有效，但平移参数 m31 和 m32 无效。看起来还有一个以场景为中心的功能。在下面的代码中，我操纵 rectScene 进行平移，但为什么我不能使用 m31 和 m32 进行平移？ (这是我的问题

'''Pan (left mouse but) and zoom (mouse wheel)  test'''
'''Python 3.4 (No differance between PyQt4 and PyQt5)'''
#from PyQt5 import QtGui, QtCore
#import PyQt5.QtWidget as QW            
from PyQt4 import QtGui, QtCore
import PyQt4.QtGui as QW            

import numpy as np                         

class ZoomAndPan(QW.QGraphicsView):

    def __init__(self,parent=None):
        super(ZoomAndPan,self).__init__(parent)
        self.setWindowTitle('ZoomAndPan')
        self.setGeometry(600,300,600,400)
        'Left button in top of image. Shows the transform matrix (press to reset)'
        self.mess = QW.QPushButton('Transform Matrix\n\n\ndx,xy\ncounter', self)
        self.mess.clicked.connect(self.resetM)

        'm31 button, adds 200 to m31'
        self.m31 = QW.QPushButton('m31', self)
        self.m31.move(200,0)
        self.m31.clicked.connect(self.addM31)

        'm13 button, adds 0.0001 to m13'
        self.m13 = QW.QPushButton('m13', self)
        self.m13.move(300,0)
        self.m13.clicked.connect(self.addM13)
        self.count=0   #Counter     

        # Create scene   
        self.sc=scene(self,self)
        self.setScene(self.sc)

    def mouseMoveEvent(self,event):
        'Pan by manipulting sceneRect'
        pos=event.pos()
        pos=self.mapToScene(pos)      
        dx=pos.x()-self.sc.startPos.x() 
        dy=pos.y()-self.sc.startPos.y()

        rect=self.sceneRect().getRect()
        self.setSceneRect(rect[0]-dx,rect[1]-dy,rect[2],rect[3])         
        # Increas counter to show that the loop works 
        self.count+=1
        self.showMatrix()

    def showMatrix(self):
        'Show matrix in Textbox (Buttton)'
        m=self.transform()
        str1='{0:5.2f}{1:5.2f} {2:6.4f}\n'.format(m.m11(), m.m12(),m.m13())
        str2='{0:5.2f}{1:5.2f}{2:5.2f}\n'.format(m.m21(), m.m22(),m.m23())
        str3='{0:5.2f}{1:5.2f}{2:5.2f}\n'.format(m.m31(), m.m32(),m.m33())
        str4='{0:5.2f}{1:5.2f}\n'.format(m.dx(), m.dy(),m.m33())
        'Show counter '
        str5='{0:5.0f}'.format(self.count)        
        self.mess.setText(str1+str2+str3+str4+str5)

    def resetM(self):
        'Reset transform'
        self.resetTransform()
        self.showMatrix()

    def addM31(self):
        'Add 200 to m31 '
        m=self.transform()
        m.setMatrix(m.m11(),m.m12(),m.m13(),m.m21(),m.m22(),m.m23(),m.m31()+200,m.m32(),m.m33())
        self.setTransform(m)    
        self.showMatrix()

    def addM13(self):
        'Add 0.0001 to m13 '
        m=self.transform()
        m.setMatrix(m.m11(),m.m12(),m.m13()+0.0001,m.m21(),m.m22(),m.m23(),
            m.m31(),m.m32(),m.m33())
        self.setTransform(m)    
        self.showMatrix()        

class scene(QW.QGraphicsScene):
    def __init__(self,parent,myView=[]):
        QW.QGraphicsScene.__init__(self,parent)
        self.myView=myView        
        # Some items in scene 
        self.txt=self.addSimpleText("///////")
        self.txt.setPos(2,-20)
        self.txt.setScale(2)
        self.txt.setBrush(QtGui.QBrush(QtCore.Qt.green))
        self.addRect(0,16,20,20, pen=QtGui.QPen(QtCore.Qt.blue))
        self.addRect(10,60,32,8, pen=QtGui.QPen(QtCore.Qt.red))
        self.addRect(30,16,20,20, pen=QtGui.QPen(QtCore.Qt.blue))
        self.N=0

    def mousePressEvent(self, event):     
        self.myView.setDragMode(1) # Works fine without this   
        self.startPos=event.scenePos()        

    def mouseReleaseEvent(self, event):     
        self.myView.setDragMode(0)

    def wheelEvent(self, event):
        'zoom'
        sc=event.delta()/100
        if sc<0: sc=-1/sc
        self.myView.scale(sc,sc)
        self.myView.setDragMode(0)
        self.myView.showMatrix()        

def main():
    app = QW.QApplication([])
    fig=ZoomAndPan()
    fig.show();
    app.exec_()


if __name__=='__main__':
    main()

Answer 1

从数学的角度来看，一切正常。您看不到任何变化的原因是 QGraphicsView 根据其 alignment property 将 View 居中.

来自Qt docs :

QGraphicsView supports affine transformations, using QTransform. You can either pass a matrix to setTransform(), or you can call one of the convenience functions rotate(), scale(), translate() or shear(). The most two common transformations are scaling, which is used to implement zooming, and rotation. QGraphicsView keeps the center of the view fixed during a transformation. Because of the scene alignment (setAligment()), translating the view will have no visual impact.