pyqt要实现这样一个功能，QGraphicsView大小固定不变，当加载的图片尺寸大于QGraphicsView时，缩放图片适应QGraphicsView，当未超过时，保持原图居中显示，然后如果点击裁剪按钮，出现一个矩形裁剪框实现裁剪功能

### PyQt 中使用 QGraphicsView 实现图片自适应缩放、居中显示和裁剪功能 在 PyQt 的 `QGraphicsView` 和 `QGraphicsScene` 组件的帮助下，可以方便地实现图片的自适应缩放、居中显示以及裁剪功能。以下是详细的解决方案： #### 自适应缩放与居中显示 为了使图片能够自动适配窗口大小并保持居中显示，可以通过设置视图的变换模式为 `KeepAspectRatio` 来确保比例不变，并利用 `fitInView()` 方法动态调整图片尺寸。 #### 裁剪功能 对于裁剪功能，可以在场景 (`QGraphicsScene`) 上绘制矩形选框，记录用户的拖拽动作以定义裁剪区域。之后提取该区域内像素数据完成裁剪操作。 下面是完整的示例代码： ```python from PyQt5.QtWidgets import QApplication, QMainWindow, QGraphicsView, QGraphicsScene, QVBoxLayout, QWidget, QPushButton, QFileDialog from PyQt5.QtGui import QPixmap, QImage, QPainter, QColor, QPen from PyQt5.QtCore import Qt, QRectF class ImageViewer(QMainWindow): def __init__(self): super().__init__() self.initUI() def initUI(self): self.setWindowTitle('Image Viewer with Crop') centralWidget = QWidget(self) layout = QVBoxLayout(centralWidget) self.view = CustomGraphicsView(self) self.scene = QGraphicsScene() self.view.setScene(self.scene) layout.addWidget(self.view) buttonLoad = QPushButton("Load Image") buttonCrop = QPushButton("Crop") buttonLoad.clicked.connect(self.loadImage) buttonCrop.clicked.connect(self.cropImage) layout.addWidget(buttonLoad) layout.addWidget(buttonCrop) self.setCentralWidget(centralWidget) def loadImage(self): options = QFileDialog.Options() fileName, _ = QFileDialog.getOpenFileName(self,"Select an image file", "", "Images (*.png *.jpg);;All Files (*)", options=options) if fileName: pixmap = QPixmap(fileName) if not pixmap.isNull(): self.image = QImage(pixmap.toImage()) self.pixmap_item = self.scene.addPixmap(pixmap) # Adjust view to fit the loaded image initially. self.view.fitInView(self.pixmap_item, Qt.KeepAspectRatio) def cropImage(self): rect = self.view.getCropRect() # Get cropped rectangle coordinates. if rect is None or self.image is None: return cropped_image = self.image.copy(rect) # Perform cropping using QImage's copy method. savePath, _ = QFileDialog.getSaveFileName(None, 'Save Cropped Image', '', '*.png;;*.jpg') if savePath and not savePath.strip().isspace(): cropped_image.save(savePath) class CustomGraphicsView(QGraphicsView): def __init__(self, parent=None): super(CustomGraphicsView, self).__init__(parent) self._is_panning = False self._pan_start_x = 0 self._pan_start_y = 0 self.start_pos = None self.end_pos = None def wheelEvent(self, event): factor = pow(1.2, event.angleDelta().y() / 240.0) self.scale(factor, factor) def resizeEvent(self, event): super().resizeEvent(event) scene_rect = self.sceneRect() if not scene_rect.isEmpty(): self.fitInView(scene_rect, Qt.KeepAspectRatio) def mousePressEvent(self, event): if event.button() == Qt.LeftButton: self.start_pos = self.mapToScene(event.pos()) # Start position of selection box. if self.itemAt(event.pos()): self._is_panning = True self._pan_start_x = event.x() self._pan_start_y = event.y() elif event.button() == Qt.RightButton: self.resetTransform() super().mousePressEvent(event) def mouseMoveEvent(self, event): if self._is_panning: delta_x = event.x() - self._pan_start_x delta_y = event.y() - self._pan_start_y self.horizontalScrollBar().setValue(self.horizontalScrollBar().value() - delta_x) self.verticalScrollBar().setValue(self.verticalScrollBar().value() - delta_y) self._pan_start_x = event.x() self._pan_start_y = event.y() else: current_pos = self.mapToScene(event.pos()) if self.start_pos: pen = QPen(Qt.red, 2) brush = QColor(255, 0, 0, 50) painter = QPainter(self.viewport()) painter.setPen(pen) painter.fillRect(QRectF(self.start_pos, current_pos), brush) super().mouseMoveEvent(event) def mouseReleaseEvent(self, event): if event.button() == Qt.LeftButton: self._is_panning = False self.end_pos = self.mapToScene(event.pos()) # End position of selection box. super().mouseReleaseEvent(event) def getCropRect(self): """Return a QRect object representing the selected area.""" if self.start_pos and self.end_pos: top_left = min(self.start_pos.x(), self.end_pos.x()), min(self.start_pos.y(), self.end_pos.y()) bottom_right = max(self.start_pos.x(), self.end_pos.x()), max(self.start_pos.y(), self.end_pos.y()) width = abs(bottom_right[0] - top_left[0]) height = abs(bottom_right[1] - top_left[1]) return QRectF(top_left[0], top_left[1], width, height).toAlignedRect() if __name__ == '__main__': app = QApplication([]) window = ImageViewer() window.showMaximized() app.exec_() ``` 此程序实现了加载图片后的自适应缩放、鼠标滚轮控制放大缩小的功能[^1]，还支持通过左键拖动选择裁剪范围，并最终保存裁剪结果到本地文件[^2]。