无法在 Qgraphics 图像上绘制矩形

Question

我正在尝试在 Qgraphics 场景上绘制矩形。我找到了很多例子，但没有一个对我有用。该矩形绘制在窗口中 Qgraphics 视图小部件未覆盖的区域上，但是当我尝试查看图像时，它无法正常工作。我不知道为什么。一个观察结果是 Qgraphicsview 鼠标释放事件没有被执行。但我无法解决问题。任何帮助都会有所帮助。提前致谢。

我正在使用的代码如下。

# -*- 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
import numpy as np
from scipy.ndimage import zoom
import cv2
from matplotlib import pyplot as plt
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"))        
        grview = self.graphicsView
        scene = QtGui.QGraphicsScene()
        pixmap = QtGui.QPixmap('Koala.jpg')
        pixmap = pixmap.scaledToHeight(420)
        scene.addPixmap(pixmap)        
        grview.setScene(scene)
        grview.show()        
        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"))    

        self.pushButton.clicked.connect(test_clipped_zoom)  

        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.pos1 = [0,0]
        self.pos2 = [0,0]
        self.show()     


    def paintEvent(self, event):
        width = self.pos2[0]-self.pos1[0]
        height = self.pos2[1] - self.pos1[1]
        qp = QtGui.QPainter()        
        qp.begin(self)           
        qp.drawRect(self.pos1[0], self.pos1[1], width, height)        
        qp.end()

    def mousePressEvent(self, event):
        self.pos1[0], self.pos1[1] = event.pos().x(), event.pos().y()
        print("clicked")

    def mouseReleaseEvent(self, event):
        self.pos2[0], self.pos2[1] = event.pos().x(), event.pos().y()
        print("released")
        self.update()            






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




if __name__ == "__main__":
    import sys
    app = QtGui.QApplication(sys.argv)

    w = Myrect()
    zoom_win_qt = QtGui.QMainWindow()
    ui = Ui_zoom_win_qt()
    ui.setupUi(zoom_win_qt)
    zoom_win_qt.show()




    sys.exit(app.exec_())

Answer 1

QGraphicsView 是一个显示场景的小部件（QGraphicsScene），所以常见的做法是在场景中添加一个矩形（就好像它是一个演员一样），而不是绘画。您还在Myrect 中绘画，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画。

另一方面，不建议修改Qt Designer生成的类，所以我冒昧地将其恢复到初始状态

回到起点，给QGraphicsScene添加一个矩形，你必须知道那些点在场景坐标系中的坐标，所以一种方法是使用eventFilter()，这个必须过滤GraphicsSceneMousePress 和 GraphicsSceneMouseRelease 事件，它们都有位置，我们可以使用 scenePos() 方法获取它。

...
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_())