PySide6中QLabel显示QMovie时保持宽高比的动态缩放教程

from PySide6.QtWidgets import QLabel
from PySide6.QtCore import Qt, QSize, QRect
from PySide6.QtGui import QMovie, QPainter, QPixmap

class ScaledLabel(QLabel):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self._movieSize = QSize()  # 存储QMovie的原始尺寸
        self._minSize = QSize()    # 存储QLabel的最小尺寸提示

    def setMovie(self, movie):
        if self.movie() == movie:
            return
        super().setMovie(movie)

        if not isinstance(movie, QMovie) or not movie.isValid():
            self._movieSize = QSize()
            self._minSize = QSize()
            self.updateGeometry()
            return

        # 存储当前帧号和播放状态，以便计算后恢复
        current_frame_number = movie.currentFrameNumber()
        movie_state = movie.state()

        # 跳转到第一帧开始计算
        movie.jumpToFrame(0)
        bounding_rect = QRect()

        # 遍历所有帧，计算所有帧的最小边界框的并集
        for i in range(movie.frameCount()):
            movie.jumpToNextFrame()
            bounding_rect |= movie.frameRect() # 使用按位或运算符来合并矩形

        # 根据合并后的边界框计算电影的原始总宽度和高度
        width = bounding_rect.x() + bounding_rect.width()
        height = bounding_rect.y() + bounding_rect.height()

        self._movieSize = QSize(width, height)

        # 根据原始尺寸计算一个合适的最小尺寸提示，以保持宽高比
        if width == 0 or height == 0: # 避免除零错误
            self._minSize = QSize(4, 4) # 默认一个小的正方形
        else:
            minimum_dim = min(width, height)
            maximum_dim = max(width, height)
            aspect_ratio = maximum_dim / minimum_dim

            # 以较小维度为基准（例如4像素），计算最小尺寸
            base_size = min(4, minimum_dim)
            self._minSize = QSize(base_size, round(base_size * aspect_ratio))

            # 如果原始宽度是较小维度，则转置最小尺寸以匹配
            if minimum_dim == width:
                self._minSize.transpose()

        # 恢复电影的原始状态
        movie.jumpToFrame(current_frame_number)
        if movie_state == movie.MovieState.Running:
            movie.setPaused(False)
        self.updateGeometry() # 通知布局系统尺寸提示已更新

    def minimumSizeHint(self):
        if self._minSize.isValid():
            return self._minSize
        return super().minimumSizeHint()

    def paintEvent(self, event):
        movie = self.movie()
        if not isinstance(movie, QMovie) or not movie.isValid():
            super().paintEvent(event)
            return

        qp = QPainter(self)
        self.drawFrame(qp) # 绘制QLabel的边框等

        content_rect = self.contentsRect() # 获取QLabel内部可用于绘制内容的区域
        margin = self.margin()
        content_rect.adjust(margin, margin, -margin, -margin) # 考虑边距

        style = self.style()
        alignment = style.visualAlignment(self.layoutDirection(), self.alignment())

        # 根据当前可用区域和电影原始尺寸，计算一个期望的缩放尺寸
        maybe_scaled_size = self._movieSize.scaled(content_rect.size(), Qt.KeepAspectRatio)

        # 优化：如果期望尺寸与QMovie当前报告的缩放尺寸不同
        if maybe_scaled_size != movie.scaledSize():
            movie.setScaledSize(maybe_scaled_size) # 告诉QMovie按此尺寸生成帧
            # 同时，显式地缩放当前帧的QPixmap进行绘制，确保立即的视觉准确性
            style.drawItemPixmap(
                qp, content_rect, alignment, 
                movie.currentPixmap().scaled(content_rect.size(), Qt.KeepAspectRatio)
            )
        else:
            # 如果QMovie已经按期望尺寸生成帧，则直接绘制当前帧的QPixmap，更高效
            style.drawItemPixmap(
                qp, content_rect, alignment, 
                movie.currentPixmap()
            )