osgEarth的Rex引擎原理分析（四十四）如何控制父子TileNode节点的显隐

最新推荐文章于 2024-01-02 21:32:33 发布

hankern

最新推荐文章于 2024-01-02 21:32:33 发布

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分类专栏： osg osgearth rex 地理信息引擎 osgEarth的Rex引擎原理分析

本文链接：https://blog.youkuaiyun.com/hankern/article/details/87418889

本文分析了osgEarth的Rex引擎如何控制父子TileNode的显隐。当一个TileNode有子节点且子节点准备就绪时，通常隐藏父节点，反之显示。此控制通过遍历Surface、TerrainCuller和DrawTileCommand来实现。文章还列举了一系列后续分析的主题，涉及osgEarth的多个方面。

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目标：（三十七）中的105

rex渲染出的地球是靠一块块TileNode瓦片拼接起来的，瓦片之间存在父子关系，一般显示父TileNode就不应显示子TileNode，反之亦然。那么rex是如何做这种显隐控制呢？

1、每一个TileNode瓦片在遍历时，会根据是否有子节点及子节点的准备情况来决定是否遍历其_surface（负责具体的显示内容）。

osgEarthDrivers/engine_rex/TileNode.cpp
bool
TileNode::cull(TerrainCuller* culler)
{

    // determine whether we can and should subdivide to a higher resolution:
    bool childrenInRange = shouldSubDivide(culler, context->getSelectionInfo());

    // whether it is OK to create child TileNodes is necessary.
    bool canCreateChildren = childrenInRange;

    // whether it is OK to load data if necessary.
    bool canLoadData = true;

    // whether to accept the current surface node and not the children.
    bool canAcceptSurface = false;
    
    // Don't create children in progressive mode until content is in place
    if ( _dirty && context->getOptions().progressive() == true )
    {
        canCreateChildren = false;
    }
    
    // If this is an inherit-viewpoint camera, we don't need it to invoke subdivision
    // because we want only the tiles loaded by the true viewpoint.
    const osg::Camera* cam = culler->getCamera();
    if ( cam && cam->getReferenceFrame() == osg::Camera::ABSOLUTE_RF_INHERIT_VIEWPOINT )
    {
        canCreateChildren = false;
        canLoadData       = false;
    }

    if (childrenInRange)
    {
        // We are in range of the child nodes. Either draw them or load them.

        // If the children don't exist, create them and inherit the parent's data.
        if ( !_childrenReady && canCreateChildren )
        {
            _mutex.lock();

            if ( !_childrenReady )
            {
                OE_START_TIMER(createChildren);
                createChildren( context );
                REPORT("TileNode::createChildren", createChildren);
                _childrenReady = true;

                // This means that you cannot start loading data immediately; must wait a frame.
                canLoadData = false;
            }

            _mutex.unlock();
        }

        // If all are ready, traverse them now.
        if ( _childrenReady )
        {
            for(int i=0; i<4; ++i)
            {
                getSubTile(i)->accept(*culler);
            }
        }

        // If we don't traverse the children, traverse this node's payload.
        else
        {
            canAcceptSurface = true;