PyQt5 QGraphicsView加载图片后，怎样框选矩形，并返回矩形在·图片上的坐标

可以通过重写QGraphicsView的mousePressEvent、mouseMoveEvent和mouseReleaseEvent来实现框选矩形的功能，并计算矩形在图片上的坐标。

具体步骤如下：

1. 创建一个继承自QGraphicsView的自定义类，并在构造函数中设置一些必要的属性，如缩放、拖拽等。

2. 重写mousePressEvent，记录下鼠标按下时的坐标点。

3. 重写mouseMoveEvent，根据鼠标移动的坐标点，动态地绘制一个矩形框选区域。

4. 重写mouseReleaseEvent，记录下鼠标松开时的坐标点，并将框选区域的四个顶点的坐标转换为图片坐标系中的坐标。

下面是一个简单的示例代码：

from PyQt5.QtGui import *
from PyQt5.QtWidgets import *
from PyQt5.QtCore import *

class ImageView(QGraphicsView):
    def __init__(self, parent=None):
        super().__init__(parent)
        self.setDragMode(QGraphicsView.ScrollHandDrag)
        self.setRenderHint(QPainter.Antialiasing)
        self.setRenderHint(QPainter.SmoothPixmapTransform)
        self.setTransformationAnchor(QGraphicsView.AnchorUnderMouse)
        self.setResizeAnchor(QGraphicsView.AnchorUnderMouse)

        self.scene = QGraphicsScene(self)
        self.setScene(self.scene)

        self.pixmap_item = QGraphicsPixmapItem()
        self.scene.addItem(self.pixmap_item)

        self.rect_item = QGraphicsRectItem()
        self.rect_item.setPen(QPen(Qt.red, 2, Qt.SolidLine))
        self.rect_item.setBrush(QBrush(Qt.transparent))
        self.scene.addItem(self.rect_item)

        self.start_point = None
        self.end_point = None

    def set_image(self, image_path):
        pixmap = QPixmap(image_path)
        self.pixmap_item.setPixmap(pixmap)
        self.setSceneRect(QRectF(pixmap.rect()))

    def mousePressEvent(self, event):
        if event.button() == Qt.LeftButton:
            self.start_point = event.pos()
            self.rect_item.setRect(QRectF(self.start_point, QSizeF()))
            self.rect_item.setVisible(True)
        super().mousePressEvent(event)

    def mouseMoveEvent(self, event):
        if self.start_point is not None:
            self.end_point = event.pos()
            rect = QRectF(self.start_point, self.end_point).normalized()
            self.rect_item.setRect(rect)
        super().mouseMoveEvent(event)

    def mouseReleaseEvent(self, event):
        if self.start_point is not None and self.end_point is not None:
            rect = QRectF(self.start_point, self.end_point).normalized()
            rect_mapped = self.mapToScene(rect).boundingRect()
            print(f"Selected rect: {rect_mapped}")
            self.start_point = None
            self.end_point = None
            self.rect_item.setVisible(False)
        super().mouseReleaseEvent(event)

在使用时，可以通过set_image方法设置要显示的图片路径，然后通过鼠标框选矩形，最后在控制台输出矩形在图片上的坐标。