QGraphicsView实现简易地图4『局部加载-地图漫游』

前文链接：QGraphicsView实现简易地图3『局部加载-地图缩放』
当鼠标拖动地图移动时，需要实时增补和删减瓦片地图，大致思路是计算地图从各方向移动时进出视口的瓦片坐标值，根据变化后的瓦片坐标值来增减地图瓦片，以下将提供实现此需求的核心代码。
1、动态演示效果

2、静态展示图片

核心代码

void MapView::moveScene()
{
	QString appPath = QApplication::applicationDirPath();
	QString dirPath = QString("%1/MapData/GaoDeMap/Map/MapPng/L0%2").arg(appPath).arg(m_curLevel + 1);
	// 视口宽度和高度
	int w = viewport()->width();
	int h = viewport()->height();

	// 计算呈现的瓦片地图左上角的场景坐标和视口坐标、呈现的瓦片地图右下角的场景坐标和视口坐标
	QPoint topLeftScenePos(m_topLeftTileCoord.x * PIXMAP_SIZE, m_topLeftTileCoord.y * PIXMAP_SIZE);
	QPointF topLeftViewPos = mapFromScene(topLeftScenePos);
	QPoint bottomRightScenePos(m_bottomRightTileCoord.x * PIXMAP_SIZE, m_bottomRightTileCoord.y * PIXMAP_SIZE);
	QPointF bottomRightViewPos = mapFromScene(bottomRightScenePos);
	
	// 1、水平瓦片坐标控制：判断最左侧瓦片是否完全进入视口、最右侧瓦片是否完全离开视口
	if (topLeftViewPos.x() > 0)
	{
		int count = qCeil(topLeftViewPos.x() / PIXMAP_SIZE);	// 左侧进入视口瓦片数量
		int oldLeftTileCoordX = m_topLeftTileCoord.x;			// 保存原左侧瓦片坐标X
		m_topLeftTileCoord.x -= count;							// 更新现左侧瓦片坐标X

		// 增加从左侧进入视口的图片
		for (int row = m_topLeftTileCoord.y; row <= m_bottomRightTileCoord.y; ++row)
		{
			for (int col = m_topLeftTileCoord.x; col < oldLeftTileCoordX; ++col)
			{
				QString fileName = QString("%1/Map_%2-%3.png").arg(dirPath)
					.arg(QString::number(row + 1).rightJustified(2, '0')).arg(QString::number(col + 1).rightJustified(2, '0'));
				QPixmap pixmap(fileName);
				QGraphicsPixmapItem *item = new QGraphicsPixmapItem(pixmap);
				item->setPos(PIXMAP_SIZE * col, PIXMAP_SIZE * row);
				m_scene->addItem(item);
				m_mapItems[row][col] = item;
			}
		}
	}
	if (bottomRightViewPos.x() > w)
	{
		int count = qFloor((bottomRightViewPos.x() - w) / PIXMAP_SIZE) + 1;	// 右侧离开视口瓦片数量
		int oldRightTileCoordX = m_bottomRightTileCoord.x;					// 保存原右侧瓦片坐标X
		m_bottomRightTileCoord.x -= count;									// 更新现右侧瓦片坐标X

		// 删除从右侧离开视口的图片
		for (int row = m_topLeftTileCoord.y; row <= m_bottomRightTileCoord.y; ++row)
		{
			for (int col = oldRightTileCoordX; col > m_bottomRightTileCoord.x; --col)
			{
				QGraphicsPixmapItem *item = m_mapItems[row][col];
				m_scene->removeItem(item);
				m_mapItems[row].remove(col);
				delete item;
			}
		}
	}

	// 2、水平瓦片坐标控制：判断最右侧瓦片是否完全进入视口、最左侧瓦片是否完全离开视口
	if (bottomRightViewPos.x() + 255 < w)
	{
		int count = qCeil((w - (bottomRightViewPos.x() + 255)) / PIXMAP_SIZE);	// 右侧进入视口瓦片数量
		int oldRightTileCoordX = m_bottomRightTileCoord.x;						// 保存原右侧瓦片坐标X
		m_bottomRightTileCoord.x += count;										// 保存现右侧瓦片坐标X

		// 增加从右侧进入视口的图片
		for (int row = m_topLeftTileCoord.y; row <= m_bottomRightTileCoord.y; ++row)
		{
			for (int col = m_bottomRightTileCoord.x; col > oldRightTileCoordX; --col)
			{
				QString fileName = QString("%1/Map_%2-%3.png").arg(dirPath)
					.arg(QString::number(row + 1).rightJustified(2, '0')).arg(QString::number(col + 1).rightJustified(2, '0'));
				QPixmap pixmap(fileName);
				QGraphicsPixmapItem *item = new QGraphicsPixmapItem(pixmap);
				item->setPos(PIXMAP_SIZE * col, PIXMAP_SIZE * row);
				m_scene->addItem(item);
				m_mapItems[row][col] = item;
			}
		}
	}

	if (topLeftViewPos.x() + 255 < 0)
	{
		int count = qFloor(fabs(topLeftViewPos.x()) / PIXMAP_SIZE);	// 左侧离开视口瓦片数量
		int oldLeftTileCoordX = m_topLeftTileCoord.x;				// 保存原左侧瓦片坐标X
		m_topLeftTileCoord.x += count;								// 保存现左侧瓦片坐标X

		// 删除从左侧离开视口的图片
		for (int row = m_topLeftTileCoord.y; row <= m_bottomRightTileCoord.y; ++row)
		{
			for (int col = oldLeftTileCoordX; col < m_topLeftTileCoord.x; ++col)
			{
				QGraphicsPixmapItem *item = m_mapItems[row][col];
				m_scene->removeItem(item);
				m_mapItems[row].remove(col);
				delete item;
			}
		}
	}

	// 3、垂直瓦片坐标控制：判断最上侧瓦片是否完全进入视口，最下侧瓦片是否完全离开视口
	if (topLeftViewPos.y() > 0)
	{
		int count = qCeil(topLeftViewPos.y() / PIXMAP_SIZE);	// 上侧进入视口瓦片数量
		int oldTopTileCoordY = m_topLeftTileCoord.y;			// 保存原上侧瓦片坐标Y
		m_topLeftTileCoord.y -= count;							// 保存现上侧瓦片坐标Y

		// 增加从上侧进入视口的图片
		for (int row = m_topLeftTileCoord.y; row < oldTopTileCoordY; ++row)
		{
			for (int col = m_topLeftTileCoord.x; col <= m_bottomRightTileCoord.x; ++col)
			{
				QString fileName = QString("%1/Map_%2-%3.png").arg(dirPath)
					.arg(QString::number(row + 1).rightJustified(2, '0')).arg(QString::number(col + 1).rightJustified(2, '0'));
				QPixmap pixmap(fileName);
				QGraphicsPixmapItem *item = new QGraphicsPixmapItem(pixmap);
				item->setPos(PIXMAP_SIZE * col, PIXMAP_SIZE * row);
				m_scene->addItem(item);
				m_mapItems[row][col] = item;
			}
		}
	}

	if (bottomRightViewPos.y() > h)
	{
		int count = qFloor((bottomRightViewPos.y() - h) / PIXMAP_SIZE) + 1;	// 下侧离开视口瓦片数量
		int oldBottomTileCoordY = m_bottomRightTileCoord.y;					// 保存原下侧瓦片坐标Y
		m_bottomRightTileCoord.y -= count;									// 保存现下侧瓦片坐标Y

		// 删除从下侧离开视口的图片
		for (int row = oldBottomTileCoordY; row > m_bottomRightTileCoord.y; --row)
		{
			for (int col = m_topLeftTileCoord.x; col <= m_bottomRightTileCoord.x; ++col)
			{
				QGraphicsPixmapItem *item = m_mapItems[row][col];
				m_scene->removeItem(item);
				m_mapItems[row].remove(col);
				delete item;
			}
		}
	}

	// 4、垂直瓦片坐标控制：判断最下侧瓦片是否完全进入视口，最上侧瓦片是否完全离开视口
	if (bottomRightViewPos.y() + 255 < h)
	{
		int count = qCeil((h - (bottomRightViewPos.y() + 255)) / PIXMAP_SIZE);	// 下侧进入视口瓦片数量
		int oldBottomTileCoordY = m_bottomRightTileCoord.y;						// 保存原下侧瓦片坐标Y
		m_bottomRightTileCoord.y += count;										// 保存现下侧瓦片坐标Y

		// 增加从下侧进入视口的图片
		for (int row = m_bottomRightTileCoord.y; row > oldBottomTileCoordY; --row)
		{
			for (int col = m_topLeftTileCoord.x; col <= m_bottomRightTileCoord.x; ++col)
			{
				QString fileName = QString("%1/Map_%2-%3.png").arg(dirPath)
					.arg(QString::number(row + 1).rightJustified(2, '0')).arg(QString::number(col + 1).rightJustified(2, '0'));
				QPixmap pixmap(fileName);
				QGraphicsPixmapItem *item = new QGraphicsPixmapItem(pixmap);
				item->setPos(PIXMAP_SIZE * col, PIXMAP_SIZE * row);
				m_scene->addItem(item);
				m_mapItems[row][col] = item;
			}
		}
	}

	if (topLeftViewPos.y() + 255 < 0)
	{
		int count = qFloor(fabs(topLeftViewPos.y()) / PIXMAP_SIZE);	// 上侧离开视口瓦片数量
		int oldTopTileCoordY = m_topLeftTileCoord.y;				// 保存原上侧瓦片坐标Y
		m_topLeftTileCoord.y += count;								// 保存现上侧瓦片坐标Y

		// 删除从上侧离开视口的图片
		for (int row = oldTopTileCoordY; row < m_topLeftTileCoord.y; ++row)
		{
			for (int col = m_topLeftTileCoord.x; col <= m_bottomRightTileCoord.x; ++col)
			{
				QGraphicsPixmapItem *item = m_mapItems[row][col];
				m_scene->removeItem(item);
				m_mapItems[row].remove(col);
				delete item;
			}
		}
	}
}