pyqt5 graphicsView 加载显示图片，在图片上鼠标框选红色矩形并返回矩形在图片上的坐标

可以通过继承 QGraphicsView 和 QGraphicsScene 类，实现在图片上框选矩形并返回矩形坐标的功能。以下是示例代码：

from PyQt5.QtWidgets import QGraphicsView, QGraphicsScene
from PyQt5.QtCore import Qt, QRectF, QPointF
from PyQt5.QtGui import QPixmap, QPen, QColor

class ImageViewer(QGraphicsView):
    def __init__(self):
        super().__init__()
        self.setScene(QGraphicsScene(self))
        self.setDragMode(QGraphicsView.ScrollHandDrag)
        self.setRenderHint(QPainter.Antialiasing)
        self.setRenderHint(QPainter.SmoothPixmapTransform)
        self.setTransformationAnchor(QGraphicsView.AnchorUnderMouse)
        self.setHorizontalScrollBarPolicy(Qt.ScrollBarAlwaysOff)
        self.setVerticalScrollBarPolicy(Qt.ScrollBarAlwaysOff)
        self.setFixedSize(800, 600)
        self._start = QPointF()
        self._rect_item = None
    
    def loadImage(self, img_path):
        pixmap = QPixmap(img_path)
        self.setSceneRect(pixmap.rect())
        self.scene().addPixmap(pixmap)
    
    def mousePressEvent(self, event):
        if event.button() == Qt.LeftButton:
            self._start = event.pos()
            pen = QPen(QColor(255, 0, 0))
            self._rect_item = self.scene().addRect(QRectF(), pen)
            self._rect_item.setZValue(1)
    
    def mouseMoveEvent(self, event):
        if event.buttons() == Qt.LeftButton:
            rect = QRectF(self._start, event.pos()).normalized()
            self._rect_item.setRect(rect)
    
    def mouseReleaseEvent(self, event):
        if event.button() == Qt.LeftButton:
            rect = self._rect_item.rect()
            img_rect = self.sceneRect()
            x = rect.x() / img_rect.width()
            y = rect.y() / img_rect.height()
            w = rect.width() / img_rect.width()
            h = rect.height() / img_rect.height()
            print("Rect coordinates:", x, y, w, h)

在以上代码中，loadImage() 方法可以将图片加载到场景中。mousePressEvent()、mouseMoveEvent() 和 mouseReleaseEvent() 方法可以实现鼠标在图片上框选矩形并记录矩形坐标的功能。其中，x、y、w、h 分别为矩形的左上角坐标和宽高的比例值，通过这些值可以计算出矩形在图片上的真实坐标。