无法在Qgraphics图像上绘制矩形

QGraphicsView 是用于显示场景的小部件( QGraphicsScene ),所以常见的做法是在场景中添加一个矩形(就像演员一样),而不是绘制。你也在 Myrect 这是其他小部件所在的小部件,因此它位于背景中,其他小部件将覆盖您所做的绘制。

另一方面,不建议修改Qt设计器生成的类,因此我冒昧地将其返回到初始状态

返回起点,将矩形添加到 Qgraphicscene 您必须知道场景坐标系中这些点的坐标,因此一种方法是使用 eventFilter() ,这必须过滤 GraphicsSceneMousePress 和 GraphicsSceneMouseRelease 事件,这些事件具有位置,我们可以使用 scenePos() 方法

...
class Myrect(QtGui.QMainWindow,Ui_zoom_win_qt):
    def __init__(self, *args, **kwargs):
        QtGui.QMainWindow.__init__(self, *args, **kwargs)
        self.setupUi(self)   
        self.pushButton.clicked.connect(test_clipped_zoom)
        self.scene = QtGui.QGraphicsScene()
        pixmap = QtGui.QPixmap('Koala.jpg').scaledToHeight(420)
        self.scene.addPixmap(pixmap)        
        self.graphicsView.setScene(self.scene) 
        self.scene.installEventFilter(self)
        self.start = QtCore.QPointF()

    def eventFilter(self, obj, event):
        if obj == self.scene:
            if event.type() == QtCore.QEvent.GraphicsSceneMousePress:
                self.start = event.scenePos()
            elif event.type() == QtCore.QEvent.GraphicsSceneMouseRelease:
                end = event.scenePos()
                self.scene.addRect(QtCore.QRectF(self.start, end))
                self.start = QtCore.QPointF()
        return QtGui.QMainWindow.eventFilter(self, obj, event)


def test_clipped_zoom():
     zoom_win_qt.hide()
     w.show()

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

完整代码:

# -*- coding: utf-8 -*-

# Form implementation generated from reading ui file 'zoom_win_qt.ui'
#
# Created by: PyQt4 UI code generator 4.11.4
#
# WARNING! All changes made in this file will be lost!

from PyQt4 import QtCore, QtGui
try:
    _fromUtf8 = QtCore.QString.fromUtf8
except AttributeError:
    def _fromUtf8(s):
        return s

try:
    _encoding = QtGui.QApplication.UnicodeUTF8
    def _translate(context, text, disambig):
        return QtGui.QApplication.translate(context, text, disambig, _encoding)
except AttributeError:
    def _translate(context, text, disambig):
        return QtGui.QApplication.translate(context, text, disambig)

class Ui_zoom_win_qt(object):
    def setupUi(self, zoom_win_qt):
        zoom_win_qt.setObjectName(_fromUtf8("zoom_win_qt"))
        zoom_win_qt.resize(800, 600)
        self.centralwidget = QtGui.QWidget(zoom_win_qt)
        self.centralwidget.setObjectName(_fromUtf8("centralwidget"))
        self.graphicsView = QtGui.QGraphicsView(self.centralwidget)
        self.graphicsView.setGeometry(QtCore.QRect(80, 40, 611, 431))
        self.graphicsView.setObjectName(_fromUtf8("graphicsView"))             
        self.horizontalSlider = QtGui.QSlider(self.centralwidget)
        self.horizontalSlider.setGeometry(QtCore.QRect(80, 500, 160, 19))
        self.horizontalSlider.setOrientation(QtCore.Qt.Horizontal)
        self.horizontalSlider.setObjectName(_fromUtf8("horizontalSlider"))
        self.progressBar = QtGui.QProgressBar(self.centralwidget)
        self.progressBar.setGeometry(QtCore.QRect(590, 490, 118, 23))
        self.progressBar.setProperty("value", 24)
        self.progressBar.setObjectName(_fromUtf8("progressBar"))
        self.pushButton = QtGui.QPushButton(self.centralwidget)
        self.pushButton.setGeometry(QtCore.QRect(380, 500, 75, 23))
        self.pushButton.setObjectName(_fromUtf8("pushButton"))    
        zoom_win_qt.setCentralWidget(self.centralwidget)
        self.menubar = QtGui.QMenuBar(zoom_win_qt)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 800, 21))
        self.menubar.setObjectName(_fromUtf8("menubar"))
        zoom_win_qt.setMenuBar(self.menubar)
        self.statusbar = QtGui.QStatusBar(zoom_win_qt)
        self.statusbar.setObjectName(_fromUtf8("statusbar"))
        zoom_win_qt.setStatusBar(self.statusbar)

        self.retranslateUi(zoom_win_qt)
        QtCore.QMetaObject.connectSlotsByName(zoom_win_qt)

    def retranslateUi(self, zoom_win_qt):
        zoom_win_qt.setWindowTitle(_translate("zoom_win_qt", "MainWindow", None))
        self.pushButton.setText(_translate("zoom_win_qt", "PushButton", None))



class Myrect(QtGui.QMainWindow,Ui_zoom_win_qt):
    def __init__(self, *args, **kwargs):
        QtGui.QMainWindow.__init__(self, *args, **kwargs)
        self.setupUi(self)   
        self.pushButton.clicked.connect(test_clipped_zoom)
        self.scene = QtGui.QGraphicsScene()
        pixmap = QtGui.QPixmap('Koala.jpg').scaledToHeight(420)
        self.scene.addPixmap(pixmap)        
        self.graphicsView.setScene(self.scene) 
        self.scene.installEventFilter(self)
        self.start = QtCore.QPointF()

    def eventFilter(self, obj, event):
        if obj == self.scene:
            if event.type() == QtCore.QEvent.GraphicsSceneMousePress:
                self.start = event.scenePos()
            elif event.type() == QtCore.QEvent.GraphicsSceneMouseRelease:
                end = event.scenePos()
                self.scene.addRect(QtCore.QRectF(self.start, end))
                self.start = QtCore.QPointF()
        return QtGui.QMainWindow.eventFilter(self, obj, event)


def test_clipped_zoom():
     zoom_win_qt.hide()
     w.show()

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