osgearth 实现雷达扫描显示的代码

osgEarth是一个开源的地理信息系统工具包，它基于OpenSceneGraph实现，可以用于开发地图应用程序。如果要在osgEarth中实现雷达扫描显示，可以通过以下步骤实现：

1. 创建一个圆柱体模型，并使用线框渲染模式。

osg::Geode* createRadarCylinder(float radius, float height)
{
    osg::Geometry* geometry = new osg::Geometry();

    osg::Vec3Array* vertices = new osg::Vec3Array();
    osg::Vec4Array* colors = new osg::Vec4Array();

    const int numSides = 36;
    const float angleDelta = 2.0f * osg::PI / (float)numSides;

    for (int i = 0; i <= numSides; i++)
    {
        float angle = i * angleDelta;
        float x = radius * sinf(angle);
        float y = radius * cosf(angle);

        vertices->push_back(osg::Vec3(x, y, 0.0f));
        colors->push_back(osg::Vec4(1.0f, 0.0f, 0.0f, 0.2f));
    }

    for (int i = 0; i <= numSides; i++)
    {
        float angle = i * angleDelta;
        float x = radius * sinf(angle);
        float y = radius * cosf(angle);

        vertices->push_back(osg::Vec3(x, y, height));
        colors->push_back(osg::Vec4(1.0f, 0.0f, 0.0f, 0.2f));
    }

    osg::DrawElementsUInt* indices = new osg::DrawElementsUInt(osg::PrimitiveSet::LINES);
    for (int i = 0; i < numSides; i++)
    {
        indices->push_back(i);
        indices->push_back(i + numSides + 1);
        indices->push_back(i + 1);

        indices->push_back(i + 1);
        indices->push_back(i + numSides + 1);
        indices->push_back(i + numSides + 2);
    }

    geometry->setVertexArray(vertices);
    geometry->setColorArray(colors);
    geometry->setColorBinding(osg::Geometry::BIND_PER_VERTEX);
    geometry->addPrimitiveSet(indices);

    osg::Geode* geode = new osg::Geode();
    geode->addDrawable(geometry);

    osg::StateSet* stateSet = geode->getOrCreateStateSet();
    stateSet->setMode(GL_LIGHTING, osg::StateAttribute::OFF);
    stateSet->setMode(GL_BLEND, osg::StateAttribute::ON);
    stateSet->setRenderingHint(osg::StateSet::TRANSPARENT_BIN);

    return geode;
}

2. 创建一个osg::ClipNode节点和一个osg::ClipPlane节点，并将圆柱体模型添加到osg::ClipNode节点中。

osg::ref_ptr<osg::ClipNode> clipNode = new osg::ClipNode();
osg::ref_ptr<osg::ClipPlane> clipPlane = new osg::ClipPlane();
clipPlane->setClipPlane(osg::Plane(0.0f, 0.0f, -1.0f, 0.0f));
clipNode->addClipPlane(clipPlane.get());
clipNode->addChild(createRadarCylinder(10.0f, 20.0f));

3. 在每一帧的渲染过程中更新osg::ClipPlane节点的位置和方向，以实现雷达扫描的效果。

osg::Matrixd matrix;
matrix.makeRotate(osg::Quat(osg::DegreesToRadians(angle), osg::Vec3(0.0f, 0.0f, 1.0f)));
osg::Vec3d position = osg::Vec3d(0.0f, 0.0f, 10.0f) * matrix;
osg::Vec3d direction = -position;
direction.normalize();
clipPlane->setClipPlane(osg::Plane(direction, position));
angle += 1.0f;

完整的示例代码如下：

#include <osg/ClipNode>
#include <osg/ClipPlane>
#include <osg/Geometry>
#include <osg/Geode>
#include <osg/MatrixTransform>
#include <osgViewer/Viewer>

osg::Geode* createRadarCylinder(float radius, float height)
{
    osg::Geometry* geometry = new osg::Geometry();

    osg::Vec3Array* vertices = new osg::Vec3Array();
    osg::Vec4Array* colors = new osg::Vec4Array();

    const int numSides = 36;
    const float angleDelta = 2.0f * osg::PI / (float)numSides;

    for (int i = 0; i <= numSides; i++)
    {
        float angle = i * angleDelta;
        float x = radius * sinf(angle);
        float y = radius * cosf(angle);

        vertices->push_back(osg::Vec3(x, y, 0.0f));
        colors->push_back(osg::Vec4(1.0f, 0.0f, 0.0f, 0.2f));
    }

    for (int i = 0; i <= numSides; i++)
    {
        float angle = i * angleDelta;
        float x = radius * sinf(angle);
        float y = radius * cosf(angle);

        vertices->push_back(osg::Vec3(x, y, height));
        colors->push_back(osg::Vec4(1.0f, 0.0f, 0.0f, 0.2f));
    }

    osg::DrawElementsUInt* indices = new osg::DrawElementsUInt(osg::PrimitiveSet::LINES);
    for (int i = 0; i < numSides; i++)
    {
        indices->push_back(i);
        indices->push_back(i + numSides + 1);
        indices->push_back(i + 1);

        indices->push_back(i + 1);
        indices->push_back(i + numSides + 1);
        indices->push_back(i + numSides + 2);
    }

    geometry->setVertexArray(vertices);
    geometry->setColorArray(colors);
    geometry->setColorBinding(osg::Geometry::BIND_PER_VERTEX);
    geometry->addPrimitiveSet(indices);

    osg::Geode* geode = new osg::Geode();
    geode->addDrawable(geometry);

    osg::StateSet* stateSet = geode->getOrCreateStateSet();
    stateSet->setMode(GL_LIGHTING, osg::StateAttribute::OFF);
    stateSet->setMode(GL_BLEND, osg::StateAttribute::ON);
    stateSet->setRenderingHint(osg::StateSet::TRANSPARENT_BIN);

    return geode;
}

int main()
{
    osgViewer::Viewer viewer;

    osg::ref_ptr<osg::ClipNode> clipNode = new osg::ClipNode();
    osg::ref_ptr<osg::ClipPlane> clipPlane = new osg::ClipPlane();
    clipPlane->setClipPlane(osg::Plane(0.0f, 0.0f, -1.0f, 0.0f));
    clipNode->addClipPlane(clipPlane.get());
    clipNode->addChild(createRadarCylinder(10.0f, 20.0f));

    osg::ref_ptr<osg::MatrixTransform> transform = new osg::MatrixTransform();
    transform->addChild(clipNode.get());

    osg::Matrixd matrix;
    matrix.makeTranslate(osg::Vec3d(0.0f, 0.0f, 500.0f));
    transform->setMatrix(matrix);

    osg::ref_ptr<osg::Group> root = new osg::Group();
    root->addChild(transform.get());

    viewer.setSceneData(root.get());
    viewer.realize();

    float angle = 0.0f;

    while (!viewer.done())
    {
        osg::Matrixd matrix;
        matrix.makeRotate(osg::Quat(osg::DegreesToRadians(angle), osg::Vec3(0.0f, 0.0f, 1.0f)));
        osg::Vec3d position = osg::Vec3d(0.0f, 0.0f, 10.0f) * matrix;
        osg::Vec3d direction = -position;
        direction.normalize();
        clipPlane->setClipPlane(osg::Plane(direction, position));
        angle += 1.0f;

        viewer.frame();
    }

    return 0;
}