osgearth 圆形扩散 代码

以下是使用osgEarth实现圆形扩散的示例代码：

#include <osgEarth/MapNode>
#include <osgEarthUtil/EarthManipulator>
#include <osgEarthUtil/ExampleResources>

#include <osg/Geode>
#include <osg/Geometry>
#include <osgViewer/Viewer>

using namespace osgEarth;
using namespace osgEarth::Util;

osg::Geometry* createCircleGeometry(float radius)
{
    osg::ref_ptr<osg::Geometry> geom = new osg::Geometry();

    osg::ref_ptr<osg::Vec3Array> vertices = new osg::Vec3Array();
    osg::ref_ptr<osg::Vec3Array> normals = new osg::Vec3Array();
    osg::ref_ptr<osg::Vec2Array> texcoords = new osg::Vec2Array();

    float step = osg::PI / 180.0f;

    for (float angle = 0.0f; angle <= 2.0f * osg::PI; angle += step)
    {
        float x = radius * std::cos(angle);
        float y = radius * std::sin(angle);

        vertices->push_back(osg::Vec3(x, y, 0.0f));
        normals->push_back(osg::Vec3(0.0f, 0.0f, 1.0f));
        texcoords->push_back(osg::Vec2(x / radius * 0.5f + 0.5f, y / radius * 0.5f + 0.5f));
    }

    geom->setVertexArray(vertices.get());
    geom->setNormalArray(normals.get());
    geom->setTexCoordArray(0, texcoords.get());
    geom->addPrimitiveSet(new osg::DrawArrays(osg::PrimitiveSet::TRIANGLE_FAN, 0, vertices->size()));

    return geom.release();
}

int main(int argc, char** argv)
{
    osg::ArgumentParser arguments(&argc, argv);

    osg::ref_ptr<osgViewer::Viewer> viewer = new osgViewer::Viewer(arguments);

    osg::ref_ptr<MapNode> mapNode = MapNode::create(Map::create());
    viewer->setSceneData(mapNode.get());

    osg::ref_ptr<EarthManipulator> manipulator = new EarthManipulator();
    viewer->setCameraManipulator(manipulator.get());

    osg::ref_ptr<osg::Geode> geode = new osg::Geode();
    geode->addDrawable(createCircleGeometry(1000.0f));

    osg::ref_ptr<osg::StateSet> stateset = geode->getOrCreateStateSet();
    stateset->setMode(GL_BLEND, osg::StateAttribute::ON);
    stateset->setRenderingHint(osg::StateSet::TRANSPARENT_BIN);

    osg::ref_ptr<osg::Depth> depth = new osg::Depth();
    depth->setWriteMask(false);
    stateset->setAttributeAndModes(depth.get(), osg::StateAttribute::ON);

    mapNode->addChild(geode.get());

    return viewer->run();
}

这段代码首先创建了一个`osg::Geometry`对象，用于存储圆形的顶点、法线和纹理坐标信息。然后使用三角扇(primitive set)绘制圆形。最后将`osg::Geometry`对象添加到场景中。为了让圆形半透明，我们使用了状态集(state set)来设置`GL_BLEND`和`TRANSPARENT_BIN`模式。同时，禁用深度写入，以避免圆形被遮挡。