前文链接：QGraphicsView实现简易地图19『迁徙图』
鹰眼视图-全图显示
能够显示所有已加载的瓦片地图，支持当前视口的范围显示器。鼠标在鹰眼视图上移动时，支持是否干预主视图地图加载两种模式，即移动时是否让主视图加载空白处的瓦片。
动态演示效果
这里演示的是鹰眼视图移动时不干预主视图的地图加载

静态展示图片

核心代码

void EagleView::paintEvent(QPaintEvent *event)
{
	QGraphicsScene *scene = m_mainView->scene();
	// 设置图像大小与场景图元边界大小一致
	QRect itemsBoundingRect = m_mainView->tilesBoundingRect();
		
	int viewW = viewport()->width();
	int viewH = viewport()->height();
	double scaleW = itemsBoundingRect.width() * 1.0 / viewW;
	double scaleH = itemsBoundingRect.height() * 1.0 / viewH;
	m_backgroundScale = qMax(scaleW, scaleH);
	double pixmapW = itemsBoundingRect.width() / m_backgroundScale;
	double pixmapH = itemsBoundingRect.height() / m_backgroundScale;

	m_backgroundRect = QRectF(0, 0, pixmapW, pixmapH);
	if (pixmapW < viewW)
		m_backgroundRect.moveLeft((viewW - pixmapW) / 2);
	if (pixmapH < viewH)
		m_backgroundRect.moveTop((viewH - pixmapH) / 2);

	// 渲染图像
	QPixmap	pixmap(pixmapW, pixmapH);
	pixmap.fill(Qt::red);
	QPainter painter;
	painter.begin(viewport());
	painter.setRenderHints(/*QPainter::Antialiasing | */QPainter::/*HighQualityAntialiasing*/SmoothPixmapTransform);
	scene->render(&painter, m_backgroundRect, itemsBoundingRect);

	// 范围指示器
	int mainViewW = m_mainView->viewport()->width();
	int mainViewH = m_mainView->viewport()->height();
	scaleW = mainViewW * 1.0 / itemsBoundingRect.width();
	scaleH = mainViewH * 1.0 / itemsBoundingRect.height();
	double scale = qMax(scaleW, scaleH);
	if (scale >= 1)
	{// 当比率>=1时，矩形导航框为整个鹰眼视图中的背景图元大小
		QPointF viewportTopLeftToScenePos = m_mainView->mapToScene(QPoint(0, 0));
		// 调整位置
		double x, y, w, h;
		if (scaleW >= 1)
		{
			w = m_backgroundRect.width();
			x = m_backgroundRect.x() + 1;
		}
		else
		{
			w = pixmapW * scaleW;
			double offsetX = m_backgroundRect.x();
			x = offsetX + (viewportTopLeftToScenePos.x() - itemsBoundingRect.x()) / itemsBoundingRect.width() * pixmapW;
		}

		if (scaleH >= 1)
		{
			h = m_backgroundRect.height();
			y = m_backgroundRect.y();
		}
		else
		{
			h = pixmapH * scaleH;
			double offsetY = m_backgroundRect.y();
			y = offsetY + (viewportTopLeftToScenePos.y() - itemsBoundingRect.y()) / itemsBoundingRect.height() * pixmapH;
		}

		m_indicatorRect = QRectF(x, y, w - 1, h);
		painter.setPen(Qt::red);
		painter.drawRect(m_indicatorRect);

		m_restrictRect = m_backgroundRect.adjusted(w / 2, h / 2, -w / 2, -h / 2);
	}
	else// scale < 1
	{// 当比率<1时，矩形导航框为主视窗中图元占整个场景图元的比率所对应的鹰眼视图大小
		QPointF viewportTopLeftToScenePos = m_mainView->mapToScene(QPoint(0, 0));
		// 调整位置
		double offsetX = m_backgroundRect.x();
		double offsetY = m_backgroundRect.y();
		double x = offsetX + (viewportTopLeftToScenePos.x() - itemsBoundingRect.x()) / itemsBoundingRect.width() * pixmapW;
		double y = offsetY + (viewportTopLeftToScenePos.y() - itemsBoundingRect.y()) / itemsBoundingRect.height() * pixmapH;
		double w = pixmapW * scaleW;
		double h = pixmapH * scaleH;
		m_indicatorRect = QRectF(x, y, w - 1, h);
		painter.setPen(Qt::red);
		painter.drawRect(m_indicatorRect);

		m_restrictRect = m_backgroundRect.adjusted(w / 2, h / 2, -w / 2, -h / 2);
	}

	QGraphicsView::paintEvent(event);
}